Development of Databases on Iodine in Foods and Dietary

Development of Databases on Iodine in Foods and
Dietary Supplements
Abby G. Ershow 1, *, Sheila A. Skeaff 2 , Joyce M. Merkel 1 and Pamela R. Pehrsson 3
Office of Dietary Supplements, National Institutes of Health, Bethesda, MD 20892, USA;
Department of Human Nutrition, University of Otago, Dunedin 9010, New Zealand;
Nutrient Data Laboratory, US Department of Agriculture, Beltsville, MD 20705, USA;
Correspondence:; Tel.: +1-301-435-2920
Received: 16 November 2017; Accepted: 10 January 2018; Published: 17 January 2018
Abstract: Iodine is an essential micronutrient required for normal growth and neurodevelopment;
thus, an adequate intake of iodine is particularly important for pregnant and lactating women, and
throughout childhood. Low levels of iodine in the soil and groundwater are common in many parts
of the world, often leading to diets that are low in iodine. Widespread salt iodization has eradicated
severe iodine deficiency, but mild-to-moderate deficiency is still prevalent even in many developed
countries. To understand patterns of iodine intake and to develop strategies for improving intake, it is
important to characterize all sources of dietary iodine, and national databases on the iodine content
of major dietary contributors (including foods, beverages, water, salts, and supplements) provide
a key information resource. This paper discusses the importance of well-constructed databases on
the iodine content of foods, beverages, and dietary supplements; the availability of iodine databases
worldwide; and factors related to variability in iodine content that should be considered when
developing such databases. We also describe current efforts in iodine database development in
the United States, the use of iodine composition data to develop food fortification policies in New
Zealand, and how iodine content databases might be used when considering the iodine intake and
status of individuals and populations.
Keywords: iodine; database; food; dietary supplements; food composition
1. Introduction
Low levels of iodine in the soil and groundwater are common in many parts of the world, often
leading to diets that are low in iodine. Severe iodine deficiency is now rare due to widespread salt
iodization, but mild-to-moderate deficiency is still prevalent even in many developed countries [1].
Knowledge about all sources of dietary iodine, including foods, beverages, water, salts, and
supplements, is important for understanding patterns of iodine intake and for planning interventions.
Robust food composition tables specific to individual countries are a key practical resource in providing
population-level and individual-level guidance for better iodine nutrition. This article will discuss the
importance of well-constructed databases on the iodine content of foods and dietary supplements, the
primary causes of variability in iodine content, the desirable characteristics of these databases, and
their current availability worldwide. We also describe recent progress in iodine database development
and use in the United States (US) and New Zealand, and consider database applications relevant to
the assessment of iodine intake of populations and individuals.
Nutrients 2018, 10, 100; doi:10.3390/nu10010100
Nutrients 2018, 10, 100
2 of 20
2. Background
Iodine is essential for the synthesis of thyroid hormone and thus is required for normal physical,
neurological, and intellectual growth of infants and children, and for normal metabolism and
function in adults. On a body weight basis, infancy and early childhood are the times of highest
iodine requirements. Pregnant and lactating women also have increased requirements to meet their
heightened physiologic needs. It is critical that women who are likely to conceive, or are pregnant or
lactating, have iodine reserves sufficient for their own health and also sufficient to provide the fetus and
infant with the necessary iodine supply [2,3]. The most serious consequences of iodine deficiency are
well characterized and include hypothyroidism, neuro-cognitive impairment, and, in cases of severe
deficiency in pregnancy, cretinism in the infant. In contrast, the consequences of mild-to-moderate
iodine deficiency are less well understood and are an important priority for research and public
health practice. In particular, concerns center on the impact of mild-to-moderate iodine deficiency
in pregnancy, which has a high prevalence worldwide [1], on child development. Two observational
studies found an association between inadequate iodine status in pregnancy and poorer academic
performance in their children [4,5], although a recent randomized controlled trial reported no difference
in cognitive scores of children born to mildly iodine deficient mothers supplemented with iodine or
placebo in pregnancy [6].
Satisfactory iodine nutrition can be achieved in most circumstances through intake of adequately
iodized salt in sufficient quantities and/or intake of other iodine-rich foods that are commonly
consumed within a country [7]. In the early 1920s, iodized table salt was introduced in many countries,
a practice that since then has spread to include the majority of countries with about 86% of the world’s
population recently estimated as having access to iodized salt [8]. World Health Organization (WHO)
recommends Universal Salt Iodization, whereby all salt for human and animal consumption is iodized
including salt used in the food industry [9]. Some countries add iodized salt to only a few foods,
for example in New Zealand and Australia, where the mandatory use of iodized salt in commercial
bread production was implemented in 2009. However, in other countries iodized salt may be available
but not used in commercially prepared food [10,11], or the salt may be iodized but at a very low
level [10].
Iodine deficiency has re-emerged in countries such as Australia [12] and New Zealand [13]. A drop
in iodine intake may reflect recent changes in food consumption patterns in which home-prepared
foods, traditionally made with iodized salt, have been replaced with commercially prepared foods
made with non-iodized salt. For example, in the case of the US, this point is reinforced by surveys
documenting that retail sales of iodized salt have declined [11] and that less time is now spent preparing
foods at home [14]. This situation has raised concerns about potentially inadequate intakes of iodine
despite high intakes of salt from commercially prepared foods [15]. Likewise, individuals or ethnic
groups whose diets exclude or restrict iodine-rich food sources for health, religious, or other reasons
(such as vegan/vegetarian diet patterns, lactose intolerance, or low salt diets) may be at risk for
inadequate iodine intake [16]. Knowing the iodine content of available foods thus becomes a key
component in understanding which foods are the most important contributors to iodine intake for
populations as well as individuals.
The need for improved data on the iodine content of foods and beverages has been noted by
several expert committees [17,18] and has recently been reviewed in detail [19]. Also, iodine derived
from dietary supplements must be included along with foods in order to accurately assess total
intake; therefore, data are needed on the iodine content of supplements [20]. Robust approaches to
developing databases will include choosing appropriate analytical methodology (including use of
standard reference materials [21,22]); designing and implementing sampling plans with good coverage
of major country-specific contributors (from foods, beverages, dietary supplements, and salt); and
publishing the results in database formats or tables that allow linkage with population surveys and
individual intake records (such as food frequency questionnaires and 24-h recalls).
Nutrients 2018, 10, 100
3 of 20
3. The Availability of Databases Including Iodine Content
Many countries have developed national databases that include information on the iodine content
of foods, beverages, and salts, and other food components. To identify food and nutrient composition
databases for individual countries and to determine if these databases included values for iodine, and
also to identify information on national iodization programs for salt or other foods, we conducted
an extensive Internet search using resources from FAO INFOODS [23], the recently released ILSI
interactive tool [24], and other sites including Google and Google Scholar. In most cases the keywords
used were “food composition”, “food composition database”, “iodine composition”, “iodine in foods”,
and the name of the country using countries listed by the US Department of State. (https://www.state.
gov/misc/list/). We did not specify any particular language in our search, although many databases
were available in English either in their original form or in translation.
Over 124 countries have known salt iodization programs, either mandatory or voluntary [25],
but for many of these countries it was not possible to determine if the country had a national food
composition database, and if so, to ascertain the presence or absence of iodine data. Table 1 presents
information on the availability of national food composition databases, by country, that have iodine
content data, and it also describes national iodization practices. Most databases provide for all kinds of
foods with a few exceptions, such as Turkey’s database, which contains iodine values only for table salt,
fish, and shellfish. However, as shown in Table 2, national iodine databases are not currently available
for many countries that do have national food composition databases containing information on other
nutrients. In some cases, limited iodine datasets have been published as part of scholarly or other
journal publications [26–31]. (NOTE: The compilation presented in Tables 1 and 2 is not exhaustive,
nor is it equivalent to a systematic literature review. The information is dynamic, meaning that at the
time of this publication, links to databases were verified to be active; however, links may change or
become inactive over time.)
Table 1. National food composition databases that include iodine.
Year of Salt
2004 [32]
Database Name
Armenian Food Composition Table 2010
AUSNUT 2011-13 Food Nutrient Database
1953/54 1 [33]
1963 [34]
OENWT Österreichische Nährwerttabelle
Food Composition Tables for the Kingdome
of Bahrain
Czech Food Composition Database
Not found 2
Czech Republic
1950 [34]
1998 [34]
Danish Food Composition Databank
1949 [34]
Fineli, National Food Composition
Database in Finland
1952 [34]
CIQUAL French Food Composition Table
Food Composition Database for
Epidemiological Studies in Italy (Banca
Dati di Composizione degli Alimenti per
Studi Epidemiologici in Italia—BDA
Tables of Food Composition in
Japan-2015-(7th Revised Ed)
1972 [35]
No program
2000 [36]
Malaysian Food Composition Database
New Zealand 3
1924 [37]
Concise New Zealand Food Composition
Tables 12th Ed
The Netherlands
1942 [34]
Dutch Nutrient Material File (NEVO)
1920 [34]
Norwegian Food Composition Table
1997 [34]
Poland Food Composition Tables Database
Nutrients 2018, 10, 100
4 of 20
Table 1. Cont.
Year of Salt
Database Name
1953 [34]
Slovak Food Composition Database Online
1964 [34]
OPKP (Open Platform for Clinical
1982 [35]
Spanish Food Composition Database
1936 [35]
Livsmedelsdatabasen—Swedish Food
Composition Database
1922 [34]
Swiss Food Composition Database
1990s [38]
Tanzania Food Composition Tables
1990s [39]
Table de Composistion des Aliments
Turkey 5
1968 [34]
Turkish Food Composition Database,
TürKomp 2
No program
Composition of Foods Integrated Dataset
Iodized salt was only added to bread in 1953/1954 but was discontinued in the 1980s; iodized salt was available
in Australia from this time. A 2009 iodization program applied to salt added to most bread [33,40]. 2 Search was
conducted and salt iodization details were not located, but this does not confirm the absence of a program. 3
Database does not have updated iodine values for all fortified breads. 4 Database lacks some milk/dairy and
beverage products. 5 Database iodine content is limited to table salt, fish, and shellfish.
Table 2. National food composition databases that do not include iodine.
Year of Salt
Source Name
1990 [34]
Belgian Table of Food Composition
No program
Brazilian Food Composition Table (TBCA)
Not found 1
Journal Publication
1949 [41]
Canadian Nutrient File (CNF)
1979 [42]
Chilean Table of Chemical Composition of
Foods, Update 2010
1995 [43]
Food and Nutrient Database,
Food Nutrition Library
Costa Rica
1970 [44]
Tablas de Composición de Alimentos
Not found 1
Tabla de Composición de Alimentos
Utilizados en Cuba
Not found 1
Food Composition Table for Use in
The Gambia
1959 [34]
German Nutrient
No program
Composition Tables of Foods and
Greek Dishes
No program
ISGEM (The Icelandic Food
Composition Database)
1983 [45]
Indian Food Composition Tables
No program
Irish Food Composition Database
No program
No program
Korean Standard Food Composition Table
Nutrients 2018, 10, 100
5 of 20
Table 2. Cont.
Year of Salt
Source Name
2000 [46]
Lesotho Food Composition Tables
Not found 1
Tablas de Composicion de Alimentos y
Productos Alimenticios Mexicanos (Version
condensada 2015)
2000 [47]
Food Composition Tables for Mozambique,
Version 2
1973 [48]
Food Composition Table for Nepal 2012
Papua New
1995 [49]
The Pacific Islands Food Composition
No program
Portuguese Food Composition Table
1937 [50]
Serbian Food & Nutrition Database
1988 [51]
Energy and Nutrient Composition of Food
South African
1995 [52]
South African Food Database System
1936 [34]
Livsmedelsdatabasen—Swedish Food
Composition Database
1994 [53]
ASEAN Food Composition Tables
Not found 1
Table de Composition des Aliments
du Togo
1990s [54]
A Food Composition Table for Central and
Eastern Uganda
1999 [55]
Bảng Thành Phần Thực Phẩm Việt Nam
Vietnamese Food Composition Table
United States
1924 [56]
USDA Food Composition Database
Search was conducted and salt iodization details were not located, but this does not confirm the absence of
a program.
4. Sources of Variability in Food Iodine Content
The amount of iodine in foods can be highly variable, and the nature and degree of this
variability can have implications for the complexity and cost of developing databases of iodine
content. For example, high variability may affect sampling plans such that more samples may need
to be collected over a wider range of geographic areas and a larger number of sales or distribution
venues [57]. Also, different chemical assay approaches (i.e., methods and reference materials) may
be needed, depending on the anticipated range of iodine concentrations. (Note: see Section 5, below,
for further discussion of these methodological issues). Highly variable and non-normal (skewed)
distributions of iodine content may be best served by presentations of descriptive statistics that include
multiple indicators of central tendency and range [58]. Some of the factors affecting between-country
and within-country variability in iodine content of foods are described below.
4.1. Water
Drinking water is particularly variable in its iodine content between and within countries,
especially if they are geographically diverse. Levels of iodine in drinking water supplies are reflective
of factors such as iodine in the soil and water table, proximity to sea water, and agricultural runoff [59].
Therefore, assessment of iodine intake from drinking water may require data at the regional or local
level. For example, the iodine content of water in some regions of China is sufficiently high to lead to
excessive intake and potential thyroid hypertrophy in school children [60]. Conversely, the desalinated
water used in many parts of Israel has been noted to have very low, essentially zero, iodine levels [61].
In many countries, there is very little information available on the iodine content of drinking water
Nutrients 2018, 10, 100
6 of 20
supplies, nor on the iodine content of bottled waters. Food composition databases should include a
range of values or a default average value for the iodine content of drinking water.
4.2. Salt
Salt is the preferred vehicle for iodine fortification, and salt iodization has been implemented in
124 countries [62]. Salt can be produced from underground rock salt deposits, natural brine, or by
evaporated seawater, with the latter containing <1 mg iodine (I)/kg of salt. This relatively low level
of iodine in un-fortified sea salt may not always be appreciated by consumers. Most food-grade salt
requires the addition of iodine, usually as potassium iodate or potassium iodide. WHO suggests that
the amount of iodine added to salt should be based on the estimated salt consumed by the population;
this ranges from 14 mg I/kg when estimated salt intake is high (i.e., 14 g/day) to 65 mg I/kg when
salt intake is low (i.e., 3 g/day) [63]. In many countries, the iodine content of iodized salt is legislated
and specified by a food standards code. However, the actual iodine content of iodized salt may differ
from the reported content, particularly when iodized salt is kept in open containers and exposed to
high humidity; the iodine content of salt can vary by 8% to 49% under such conditions [64]. Database
developers must consider whether the country practices Universal Salt Iodization, in which case all
salt for human use must be iodized, and therefore iodized salt will be used for commercial food
products [9]. Alternatively, databases might include paired iodine values for some food products that
have been prepared with iodized or non-iodized salt.
4.3. Agricultural Practices—Soils and Crops
Iodine occurs naturally in the earth’s crust and is present everywhere in the environment. Soils,
shales, and coal rich in organic matter are generally higher in iodine than hard rock [65,66]. Also
the iodine content of the soil can be influenced by the proximity of the growing area to ocean water
(through which atmospheric iodine is incorporated into rainfall, and thereby raises the iodine content
of the soil), the iodine content of ground waters and irrigation waters, and the use of iodine-containing
fertilizers [67]. The iodine content of plant crops is affected by the content of iodine in the soil (i.e.,
plants grown on high iodine soils will contain more iodine than those grown on low iodine soils), but
in general, plant-based foods such as vegetables and fruits are relatively poor sources of iodine [59].
The exceptions are seaweeds, which have a great capacity to concentrate iodine [68–70].
4.4. Agricultural Practices—Animal Husbandry
Dairy products and eggs may contain significant but variable amounts of iodine, influenced, to
some degree, by the iodine content of supplements in animal feeds and salt licks. These supplements
are often provided as part of animal husbandry practice to ensure good health and reproductive
outcomes in dairy and beef cattle, sheep, goats, and poultry. Dairy products also have contained
adventitious iodine from iodophors, iodine-containing disinfectants used at various points in the
production of milk. Iodophors can be used to clean udders, but if the cleansing has not been performed
properly some of the iodine from the teat dips can be absorbed and transferred to milk and meat.
A recent US Department of Agriculture (USDA) report found that 55% of dairy operations were using
iodophor teat dips [71], suggesting that the practice is still relatively common in the US. Iodophors
were also used in the cleaning of industrial equipment for processing milk in dairies; a decline in
this practice in New Zealand by the mid-1980s is suggested to be responsible for a drop in the iodine
content of milk and dairy products [13].
4.5. Food Processing
Commercial baked goods are another source of iodine when iodates are used in the commercial
baking industry as dough conditioners. Iodates were introduced in the US 40 years ago and in
Tasmania, Australia, over 50 years ago, but now other dough conditioners are being used. Also, some
Nutrients 2018, 10, 100
7 of 20
commercial baked goods contain erythrosine (Red No. 3/E127), a common food coloring that contains
iodine; however, the iodine from erythrosine is only partially bioavailable [72].
5. Developing an Iodine Database for US Foods—Recent Progress
In 2014, the National Institutes of Health’s Office of Dietary Supplements (ODS), Bethesda MD,
convened several working groups to consider clinical and population research relevant to human
iodine nutrition, particularly in the US [73]. Key areas of applied and clinical research that were
reviewed and identified as needing greater effort included: assessing the iodine concentration of US
foods and drinking water supplies; evaluating iodine intakes of various US population subgroups; and
having a sufficient scientific knowledge base to determine iodine requirements at different lifecycle
stages [73]. A database on the iodine content of US foods was considered to be a critical tool for
conducting research on all of the identified gap areas. This priority has been operationalized through
an interagency agreement (NIH IAA-AOD-17002) between ODS and the USDA to develop the USDA
Food Iodine Database. Other federal partners involved in this project include the US Food and Drug
Administration and the National Institute of Standards and Technology (NIST).
In this section, as summarized in Table 3, we will describe the main features of the project plan
for the nascent USDA Food Iodine Database. A similar scientific and technical approach has been
used to develop other databases, including those for choline and flavonoids [74,75]. We note that the
scientific and technical approach used by the USDA is, of course, most suitable for the US; however,
the concepts and operational components driving the design and execution of the project plan can
serve as a prototype for development of iodine databases in other countries.
Table 3. Project Components for Developing the USDA Food Iodine Database.
Design phase (Completed)
Define research needs
Review existing data
Assess iodine distribution in the food supply
Develop sampling design and calculate sample sizes
Preliminary study phase (Completed)
Conduct stability studies
Develop sample handling protocols
Identify appropriate analytical methods and quality control materials
Research implementation phase (Ongoing)
Conduct analyses and data quality control reviews
Conduct ancillary studies
Disseminate data and documentation
5.1. The Design Phase
For any research initiative designed to provide foundational data to explore the connection
between food and health, the researcher must address what and why it needs to be done, and how to
achieve the answers. Put another way, when developing a new database or dataset, it is important
to define the research needs and potential impact at the outset of the project. In the case of iodine,
sufficient iodine composition data on food and dietary supplements are needed to estimate intakes
and to assess the consequences of deficiency or excess.
Preliminary planning activities include: identifying the “population of interest” of foods and
supplements; designing the sampling plan; developing a defensible analytical process (methods
and quality control); planning for statistical analysis of the results; and considering a means of data
dissemination. In the case of iodine, although the USDA has developed special databases for other
nutrient-focused datasets, it was important to identify unique characteristics of iodine-contributing
Nutrients 2018, 10, 100
8 of 20
foods and dietary supplements. Other specific challenges related to database development included
the need for methods for effective sampling and analysis of foods [19], and for statistical approaches
that can accommodate variability in the iodine content of foods [58].
Since resources for composition analyses are rarely sufficient to analyze all potential contributors
to iodine intake, it is essential to identify existing useable data of adequate scientific quality. The USDA
has long sought to take advantage of published and other available data when data quality criteria
have been met to satisfaction [76]. Also, for this same reason of efficiency, when possible, the USDA
seeks to harmonize its data with other data generated by complementary activities, most notably,
the US Food and Drug Administration (FDA) Total Diet Study (TDS). The FDA TDS is an ongoing
program that obtains about 290 foods of various matrices, four times a year, each in a different US
location, sampled in order to monitor an array of nutrients and other constituents of the US food
supply [77]. For iodine analysis of TDS foods, the FDA has recently synchronized their laboratory assay
method, inductively coupled-mass spectrometry (ICP-MS), to that used by the USDA; in addition,
the possibility of coordinating selected efforts is under discussion. This approach allows inter-agency
exchange of data on iodine. Also, enhanced quality control is achieved through close collaboration
to utilize NIST standard reference materials and methods. Thus, existing data from the TDS will
be used to enhance the national iodine dataset and also to set priorities for planned new or repeat
analyses [19]. When planning the sampling of specific foods, it is critical to identify and acquire other
relevant data that clarifies the distribution of iodine in the food supply (e.g., industry uses, agricultural
production, sales, and other sources). Another step involves preparing country-specific proportional
weighting factors for different versions of the food; an example would the use of industry data on
relative amounts sold or used of different types of iodized and non-iodized salt (e.g., conventional, sea,
Kosher, etc.).
In developing the sampling plan, it is necessary to determine an appropriate sample size.
The acquired food samples must be nationally representative, and the number of samples must be
sufficiently large to develop statistically defensible variability estimates. The approach to this plan must
be suitable for the country whose food supply is being analyzed; countries with a highly structured and
nationally distributed food supply will need an approach different from that in countries where foods
are acquired (grown, hunted, or foraged) and consumed within multiple smaller localities. An example
of necessary adaptations is that of acquiring food samples from American Indian reservations and
Alaska Native villages [78]. In the US, the sampling plan includes identification and procurement of
US-representative food samples; many of these samples are selected for analysis under the NIH-USDA
National Food and Nutrient Analysis Program (NFNAP) [79]. The USDA typically acquires its
food samples in a minimum of 12 geographically diverse locations selected according to current
population density data, retail sales data, and other national-level information. NFNAP foods under
evaluation for iodine analysis include finfish and other seafood products; seaweeds/seaweed extracts;
iodine-containing commercial ingredients and additives; highly-consumed dairy and egg products,
commercially processed mixed dishes; retail salts; and other foods containing significant amounts
of iodine.
5.2. Preliminary Study Phase
It is necessary to confirm the stability of the analytes in both new and archived analytical samples,
particularly when samples are shared from other studies or have been stored for some time. This is a
particularly important step when analyzing for iodine in salt and other food substrates. To investigate
the possible loss of iodine during sample storage, the USDA reanalyzed a set of samples that had
been initially analyzed 5 years previously and was able to confirm that the iodine content of archived
NFNAP foods stored at −60 ◦ C had not changed [78,80]. The USDA also plans to evaluate salt industry
data regarding iodine volatilization under varying storage, humidity, and temperature conditions.
Sample handling protocols must be developed prior to sample collection to ensure sample
integrity during shipping and storage. Pilot testing of protocols including chain-of-custody plans may
Nutrients 2018, 10, 100
9 of 20
be warranted to ensure that sample integrity can be maintained from the point of purchase all the way
through to analysis. The USDA has developed sample handling protocols for NFNAP that can serve
as examples for others who are undertaking collection and eventual assay of foods [76]. An important
precaution when utilizing samples of varying provenance (such as from a multicenter study) is to
ensure that there has not been inadvertent contamination during the collection or storage process;
sources of contamination may include leaching from storage containers that can release iodine into the
sample over time and use of iodine-containing preservatives or disinfectants.
For the chemical analysis of foods, it is important to identify appropriate analytical methods and
to select a capable laboratory through precertification testing with blinded samples [75]. In terms
of analytical methodology, the ICP-MS method [76] is suitable for the analysis of iodine in a variety
of foods, as well as dietary supplements, and is known to have good precision and accuracy. Using
the ICP-MS method, the USDA contract laboratory has shown that it can generate accurate iodine
values that compare well with the iodine values of several NIST-certified reference materials (CRM),
notably NIST 1849a Infant/Adult Nutritional Formula and 1548a Typical Diet [21,78,80]. For quality
control during analysis of samples, the USDA is using these CRM reference materials, as well as
in-house control materials cross-validated to the NIST materials. Other NIST CRM materials with
available iodine values (such as iodized salt, egg powder, whole milk powder, and kelp) will be used
as warranted as the analytical plan progresses.
5.3. Research Implementation Phase
The USDA’s experience with other database development projects has revealed that the greatest
effort and cost are incurred when acquiring food products according to the statistical design, conducting
direct assays of the prepared samples and quality control materials, and assembling the data in an
orderly format. This phase of the USDA Food Iodine Database project is now in progress. To date, over
135 unique foods have been sampled; some of these are newly acquired and others are existing frozen
samples that were archived as part of previously completed projects. About 350 prepared samples
representing these foods have been analyzed to date, along with quality control materials comprising
about 10% of total assays. The predominant food groups analyzed so far are multi-ingredient
commercial foods (e.g., restaurant hamburgers and macaroni and cheese, retail frozen pizza, milks and
yogurt) and several types of fish (shellfish, crustaceans, mollusks, and finfish).
Following data quality review, data dissemination in the form of accessible databases and
professional and peer-reviewed publications will allow transparency of the data and related
information. Additional ancillary studies can enhance the value and usefulness of database resources;
for example, the USDA is considering a sub-study to utilize direct chemical assay followed by statistical
modeling to evaluate the iodine content of home-prepared recipes in comparison with commercial
food equivalents. In addition, the USDA will use ancillary studies to explore other factors that that
may affect total dietary iodine such as geographic origin of foodstuffs (as reflecting iodine content of
soils), the iodine content of water supplies used for drinking and reconstituting foods, and the iodine
content of dietary supplements.
6. Iodine Content of Supplements
Nutrient-containing supplements may contribute substantially to total nutrient intake [27,81,82],
and therefore should be included along with foods when estimating total dietary intake of
iodine. Supplements are used worldwide but are regulated very differently among countries [83],
sometimes as foods (as in the US and Europe) [84,85], and sometimes as a form of herbal
medicines (as in Germany) [86,87], and product registration or licensing may be required under
certain circumstances [88]. Databases describing the content, ingredients, and other information
on supplements may be assembled by government entities, manufacturers, or researchers.
The information content, definitions, terminology, data formats, and sources of data can vary
Nutrients 2018, 10, 100
10 of 20
considerably, and this lack of uniformity and consistency has been noted as a limitation in making
between-country comparisons for research and other purposes [85].
Identifying and then accessing dietary supplement databases from different countries can be
challenging as there are few readily available and comprehensive compilations [85]. Nevertheless,
the task may be approached on a country-by-country basis. For example, the Netherlands provides
a database on the composition of supplements that is linked to the national food composition
tables [89]; this database has been used as part of an iodine intake assessment study in children
and adults [90]. Similarly, dietary supplement databases have been developed and then used for iodine
intake assessment in pregnant and lactating women in Norway [26–28] and in pregnant women [29]
and adults [30] in Denmark. The Australian dietary supplement database (AUSNUT 2011–2013)
contains 35 nutrient values, including iodine, for 2163 dietary supplements consumed during several
national nutrition and physical activity surveys conducted from 2011–2013 [91]. The method for
constructing a dietary supplement database for adult participants in one of the United Kingdom
sub-projects of a multi-country European cohort study has been described in detail [92].
In the US, the Dietary Supplement Label Database (DSLD), sponsored by ODS in collaboration
with other US federal agencies, is presently the most comprehensive listing of label information
( [93,94]. The DSLD evolved from earlier questionnaire-based
efforts to understand the magnitude of the contribution of supplements to population nutrient intake
in the US, starting with the 1999 cycle of the National Health and Nutrition Examination Survey
(NHANES) [93,95]. Other currently available databases with label information for US products
include DailyMed ( and the industry-sponsored Supplement Online
Wellness Library (OWL) database (
Iodine content (per serving) and source (ingredients) are provided for US supplement products
as listed on the product label and the Supplement Facts Panel [96]. For example, the label may
indicate that the iodine in the supplement product may come from diverse sources such as iodine salts
(e.g., potassium iodide) or botanical ingredients (e.g., kelp). When using label information, whether
by direct inspection of the product container or through the label databases mentioned above, an
important caveat is that results from direct analysis of individual supplement products usually are not
publicly available.
To estimate typical nutrient content values—including for iodine—for certain grouped classes of
sampled supplement products (e.g., adult multivitamin/multiminerals (MVMs), pediatric MVMs, and
non-prescription prenatal MVMs), direct chemical analysis has been conducted on sampled products
and standard reference materials [97]; the analysis results have been made available through the Dietary
Supplements Ingredient Database (DSID) [20,98]. The DSID assay results suggest that the actual iodine
content for adult MVMs, pediatric MVMs, and non-prescription prenatal MVMs may typically exceed
the labeled amount by 20–26%. Furthermore, comparisons of labeled iodine contents of prescription
and non-prescription prenatal supplements sold in the US have found that, per tablet, non-prescription
prenatals contain approximately 10% more iodine than prescription prenatals [99,100].
Given the concerns about the adequacy of iodine intake by pregnant women, data from the
US National Health and Nutrition Examination Survey (NHANES) program has provided a means
of understanding the contribution of dietary supplements to iodine intake. Use of supplements
(multi-vitamins or MVMs) was found to be widespread (~75%) among US pregnant women surveyed
in 1999–2006; however, use of iodine-containing supplements was relatively low (~22%) [95]. Since
that time, various professional organizations including the American Academy of Pediatrics [101], the
Endocrine Society [102], the Teratology Association [103], and the American Thyroid Association [104],
as well as the Australian National Health and Medical Research Council [105] and the New Zealand
Ministry of Health [106], have recommended that pregnant and lactating women take a daily prenatal
MVM supplement that contains 150 µg of iodine. Data on time trends in usage of iodine-containing
supplements by pregnant and lactating women will help in understanding whether usage is changing
in response to professional recommendations. A recent study undertaken in New Zealand reported
Nutrients 2018, 10, 100
11 of 20
that 52% of pregnant and lactating women followed the recommendation for a 150 µg of iodine per
day [107].
7. New Zealand: A Case Study Illustrating the Need for a Database with Iodine Content
New Zealand has low levels of iodine in the soil, predisposing the population to iodine deficiency.
New Zealand was the first country after Switzerland to introduce iodized salt to address widespread
iodine deficiency, albeit at an initial low concentration of 5 mg I/kg; this was increased to 50 mg I/kg in
1939 [37]. Domestic household use of iodized salt, both at the table and in home cooking, successfully
eradicated iodine deficiency in New Zealand by the early 1950s. Additional iodine was derived from
dairy products when iodophors were used by the dairy industry from the 1960s to the 1980s. However,
changes in food habits, including a reduction in the consumption of iodized salt in the home and a
drop in the iodine content of dairy products when detergent-based sanitizers replaced iodophors, are
factors believed to have contributed to the re-emergence of mild iodine deficiency in the 1990s [13].
Given the widespread nature of the deficiency, which was reported in all population groups, the most
effective strategy identified by the government was mandatory fortification [41].
Dietary modeling was used to identify the best dietary approach to increase iodine intake without
exceeding the upper limit of intake, with a particular focus on reducing the prevalence of iodine
deficiency in pregnant women and children. In order to undertake this process, it was imperative
that the iodine content of foods be included in the New Zealand Food Composition Database [108].
Because the most commonly eaten staple foods in the New Zealand diet are low in iodine, and the
foods highest in iodine content are consumed in small quantities, a preliminary proposal was put
forward to mandate the replacement of non-iodized salt with iodized salt in breads, breakfast cereals,
and sweet biscuits (i.e., cookies). Because New Zealand imports and exports biscuits, a requirement
to fortify biscuits with iodine would require separate production lines for both overseas and New
Zealand biscuit producers. Furthermore, cereal manufacturers suggested that the application of a
brine spray to breakfast cereals would produce inconsistent amounts of iodine in breakfast cereals.
Thus, concerns about trade regulations for biscuits and technological concerns for breakfast cereal
meant that bread, a staple food consumed by 87% of the New Zealand population, was chosen as the
sole food for fortification; it was acknowledged that bread would not provide pregnant women with
enough iodine to meet their higher requirements. A change to the Food Standards Code came into
effect in September 2009 mandating the use of iodized salt in yeast-leavened bread; organic bread
was exempt from this requirement [33]. The New Zealand Food Composition Database has included
a revised iodine content for some breads, although more information on the iodine content of New
Zealand breads can be found in a separate government report [109].
8. Discussion
Iodine has emerged as a nutrient of concern in many developed countries, in part because retail
sales (and home use) of non-iodized salts may be increasing [11,110–112] and iodized salt is not
always used in the commercially prepared foods that make up an ever-increasing component of the
food supply yet whose consumption often leads to excessive sodium intake [11,110–112]. Also, some
countries have not yet implemented mandatory salt iodization programs [51,112,113]. Pregnant women
and young children are at highest risk of inadequate intake but other groups within populations may
also be at risk. At present there is no simple or reliable way to assess the iodine status of an individual.
Although other causes cannot be ruled out, altered thyroid function can suggest the presence of iodine
deficiency. In the future, validated biomarkers of individual status (such as thyroglobulin levels) may
become available [114]. In the meantime, despite the difficulty of directly assessing iodine status of
individuals, practical diet-based approaches may prove useful.
Individuals should be asked about the voluntary and involuntary factors that can affect iodine
intake and status. This information can provide a basis for assessing risk and providing counseling.
For example, interview methodology can be used to gather information on use of iodine-containing
Nutrients 2018, 10, 100
12 of 20
dietary supplements, and on intake of food sources of iodine such as dairy products and seafood,
including fresh and saltwater fish and seaweeds. A growing concern in many countries is the
adoption of dietary patterns that specifically exclude major sources of iodine, including low-salt [115],
vegan [116–118], and Paleo diets [119]. Questionnaires must be attuned to phrasing; for example, it is
important to enquire about use of dairy vs non-dairy milks, as the iodine content of milk alternatives
often is very low [120]. In some situations, it may even be desirable to develop individualized advice
regarding type of salt; for example, researchers in China are attempting to develop an online screening
tool that informs consumers if they should consume iodized or non-iodized salt [121].
An additional topic that needs appropriate interview methodology includes the type of salt used
in the home for cooking and at the table. For example, interviewers should ask how often new iodized
salt is purchased, as the iodine content may decline over long periods of storage. Interviewers should
also ascertain use of sea salt, which, if not fortified, may have a surprisingly low iodine content.
Determining the amount of iodine coming from iodized cooking and table salt can be difficult to
quantify for a number of reasons. Firstly, the interpretation of a sprinkle or pinch of salt will vary
from person to person. Secondly, if food intake is being weighed, the weighing scales may not be
sensitive enough to measure salt added at the table and weight recorded as null (i.e., 0) grams. Thirdly,
when iodized salt is used for cooking vegetables or pasta, the amount of iodine in water that is
discarded and the amount that becomes incorporated into the cooked food is unknown. Thus, iodine
intakes determined using diet records or 24-h recalls are likely to underestimate actual iodine intake,
particularly in individuals who regularly and generously add iodized salt to their food. A simpler
approach is to add a set amount of iodine to anyone who reports use of iodized discretionary salt; in
New Zealand, an additional 48 µg of iodine, representing the consumption of 1 g of salt (48 mg I/kg)
per day, is included in the total daily iodine intake to account for discretionary use of iodized salt [109].
Data on the iodine content of foods can also be useful in research settings. Although seldom
considered, an estimate of the iodine content of the diet determined using a validated iodine-specific
food frequency questionnaire should be included as a variable in studies investigating thyroid function
on disease and child development. The iodine content of the diet could also be used to stratify
participants in randomized controlled trials of iodine supplementation.
Another use of iodine databases is in the treatment of thyroid disease. Patients undergoing
radioablation treatment for thyroid cancer are prescribed a several-week course of a low iodine diet,
in order to enhance uptake of radioactive iodine [122,123]. The degree of success in reducing iodine
intake usually is estimated using urinary iodine excretion [124]. Some patients find it difficult to
adhere to these diets. Also, there is debate about the necessary degree of dietary restriction, as well
as about the optimal time frame for dietary modification, both of which may depend, in part, on the
background iodine content of the patient’s usual diet [125,126]. In some circumstances, iodine data
from other countries has been used to develop dietary prescriptions for patients living in a different
country [127]. Improved national-level databases will be useful in clinical practice and in research on
low iodine diets.
Goitrogens are a chemically diverse group of compounds that have the capacity to interfere
with uptake or utilization of iodine by the thyroid gland, and thus pose an additional source of
dietary complexity important for understanding issues of adequacy of iodine intake [18]. The impact
on thyroid status of eating these foods may depend on the quantity eaten and the background
iodine content of the diet. High goitrogen intake may render marginal iodine intakes inadequate
for physiologic demands and under some circumstances may actually contribute to goiter endemics
and related disorders [128]. Dietary goitrogens often are inherent botanical constituents of foods;
examples include cassava (cyanogenic glucosides), cruciferous vegetables (glucosinolates), and soy
products (flavonoids). Dietary assessments should include information on intake of goitrogen-source
foods, which can be very specific to geographic region, including cultural practices and economic
issues related to the cost of foods. Special purpose databases or data tables with information on some
of the goitrogenic constituents of foods (e.g., the USDA Flavonoid Database [74,129]) can provide
Nutrients 2018, 10, 100
13 of 20
useful corollaries for iodine composition tables and would have potential application for research and
for counseling individuals at risk for thyroid disease. Environmental goitrogens also may present
dietary exposures of concern in some situations and include perchlorates, nitrates, and disulfides.
These compounds may derive from industrial contamination but may also occur naturally in soils and
can subsequently leach into the water supply and thereby into foods [130]. Tobacco smoke presents
another important goitrogenic exposure due to its thiocyanate content. As individuals are unlikely
to be aware of ingestion of most environmental goitrogens, it may be useful to consider estimating
exposure through the use of biomarkers [131,132].
In the US, the USDA Food Iodine Database project described in this paper complements the
ODS-supported DSID and DSLD resources that provide data on the iodine content of supplements,
necessary to determine total iodine intake. Once the USDA Food Iodine Database is complete, it will
be possible to generate more complete estimates of iodine intake and iodine sources through linkage
to dietary intake tools and to the data generated by surveys such as the NHANES, which heretofore
has based its estimates of iodine intake on urinary iodine levels [133]. Also, the eventual availability of
iodine values for a large number of foods with descriptive statistics that include multiple measures
of variability (e.g., percentile cutoffs, coefficients of variation, and standard deviation) and central
tendency (e.g., means and medians) will allow modeling of intakes that account for the spread of
iodine levels in many types of foods, thus helping to develop appropriate methods for estimating
intake of individuals and populations [58].
Another US concern, which also may be the case in other countries, is that information is available
about the iodine content of infant formula but not breast milk. Databases on the typical iodine content
of human milk would be desirable. Estimating the likely iodine intake of breast-fed infants is an
additional key aspect of understanding adequacy of population level iodine status.
9. Conclusions
Information about the iodine content of national food supplies is essential for understanding the
state of human iodine nutrition around the world, with important applications in nutrition research,
dietary counseling, treatment of thyroid disease, and public health practice. Collection and evaluation
of dietary data are essential components of this work because there is no simple way at present to
estimate iodine status of individuals. When possible, iodine composition databases for foods should
be complemented by databases for dietary supplements in countries where supplements make a
significant contribution to the total intake of iodine. Regularly updated composition data that reflect
current food supplies are needed to support nutrition surveys, which generate critical data resources
for understanding national-level concerns and identifying sub-populations at risk due to typical dietary
patterns or increased physiological need. In future surveys, characterizing the relationship between
iodine intake and thyroid function across populations and within population subgroups will require
information on total intake, from all sources.
Acknowledgments: We would like to acknowledge the assistance of Amanda Moran, University of Maryland.
This paper was supported by the NIH Office of Dietary Supplements.
Author Contributions: A.G.E., S.A.S. and P.R.P. developed the concept for the manuscript. A.G.E., S.A.S., J.M.M.
and P.R.P. wrote the manuscript.
Conflicts of Interest: The authors declare no conflicts of interest.
Iodine Global Network. Global Scorecard of Iodine Nutrition in 2017 in the General Population and in
Pregnant Women (PW). Available online:
and_PW_May2017.pdf (accessed on 20 September 2017).
Boyages, S.C. Clinical review 49: Iodine deficiency disorders. J. Clin. Endocrinol. Metab. 1993, 77, 587–591.
Nutrients 2018, 10, 100
14 of 20
Abel, M.H.; Caspersen, I.H.; Meltzer, H.M.; Haugen, M.; Brandlistuen, R.E.; Aase, H.; Alexander, J.;
Torheim, L.E.; Brantsaeter, A.L. Suboptimal maternal iodine intake is associated with impaired child
neurodevelopment at 3 years of age in the Norwegian mother and child cohort study. J. Nutr. 2017,
147, 1314–1324. [CrossRef] [PubMed]
Bath, S.C.; Steer, C.D.; Golding, J.; Emmett, P.; Rayman, M.P. Effect of inadequate iodine status in UK
pregnant women on cognitive outcomes in their children: Results from the Avon Longitudinal Study of
Parents and Children (ALSPAC). Lancet 2013, 382, 331–337. [CrossRef]
Hynes, K.L.; Otahal, P.; Hay, I.; Burgess, J.R. Mild iodine deficiency during pregnancy is associated with
reduced educational outcomes in the offspring: 9-Year follow-up of the gestational iodine cohort. J. Clin.
Endocrinol. Metab. 2013, 98, 1954–1962. [CrossRef] [PubMed]
Gowachirapant, S.; Jaiswal, N.; Melse-Boonstra, A.; Galetti, V.; Stinca, S.; Mackenzie, I.; Thomas, S.;
Thomas, T.; Winichagoon, P.; Srinivasan, K.; et al. Effect of iodine supplementation in pregnant women on
child neurodevelopment: A randomised, double-blind, placebo-controlled trial. Lancet Diabetes Endocrinol.
2017, 5, 853–863. [CrossRef]
Zimmermann, M.B. Iodine deficiency. Endocr. Rev. 2009, 30, 376–408. [CrossRef] [PubMed]
United Nations International Children’s Emergency Fund (UNICEF). Household Consumption of Iodized
Salt: Global Database 2017. Available online:
(accessed on 18 December 2017).
Venkatesh Mannar, M.G.; Dunn, J.T.; International Council for Control of Iodine Deficiency Disorders. Salt
Iodization for the Elimination of Iodine Deficiency. Available online:
production/00_mp/SI_elim_IDD_1994venkatesh.pdf (accessed on 21 December 2017).
Dahl, L.; Johansson, L.; Julshamn, K.; Meltzer, H.M. The iodine content of Norwegian foods and diets.
Public Health Nutr. 2004, 7, 569–576. [CrossRef] [PubMed]
Maalouf, J.; Barron, J.; Gunn, J.P.; Yuan, K.; Perrine, C.G.; Cogswell, M.E. Iodized salt sales in the United
States. Nutrients 2015, 7, 1691–1695. [CrossRef] [PubMed]
Li, M.; Eastman, C.J.; Waite, K.V.; Ma, G.; Zacharin, M.R.; Topliss, D.J.; Harding, P.E.; Walsh, J.P.; Ward, L.C.;
Mortimer, R.H.; et al. Are Australian children iodine deficient? Results of the Australian National Iodine
Nutrition Study. Med. J. Aust. 2006, 184, 165–169. [PubMed]
Mann, J.I.; Aitken, E. The re-emergence of iodine deficiency in New Zealand? N. Z. Med. J. 2003, 116, U351.
Smith, L.P.; Ng, S.W.; Popkin, B.M. Trends in US home food preparation and consumption: Analysis of
national nutrition surveys and time use studies from 1965–1966 to 2007–2008. Nutr. J. 2013, 12, 45. [CrossRef]
Institute of Medicine Committee on Strategies to Reduce Sodium Intake. The National Academies Collection:
Reports funded by National Institutes of Health. In Strategies to Reduce Sodium Intake in the United States;
Henney, J.E., Taylor, C.L., Boon, C.S., Eds.; National Academies Press: Washington, DC, USA, 2010.
Booms, S.; Hill, E.; Kulhanek, L.; Vredeveld, J.; Gregg, B. Iodine deficiency and hypothyroidism from
voluntary diet restrictions in the US: Case reports. Pediatrics 2016, 137, e20154003. [CrossRef] [PubMed]
Swanson, C.A.; Zimmermann, M.B.; Skeaff, S.; Pearce, E.N.; Dwyer, J.T.; Trumbo, P.R.; Zehaluk, C.;
Andrews, K.W.; Carriquiry, A.; Caldwell, K.L.; et al. Summary of an NIH workshop to identify research
needs to improve the monitoring of iodine status in the United States and to inform the DRI. J. Nutr. 2012,
142, 1175s–1185s. [CrossRef] [PubMed]
Rohner, F.; Zimmermann, M.; Jooste, P.; Pandav, C.; Caldwell, K.; Raghavan, R.; Raiten, D.J. Biomarkers of
nutrition for development—Iodine review. J. Nutr. 2014, 144, 1322s–1342s. [CrossRef] [PubMed]
Pehrsson, P.R.; Patterson, K.Y.; Spungen, J.H.; Wirtz, M.S.; Andrews, K.W.; Dwyer, J.T.; Swanson, C.A. Iodine
in food- and dietary supplement-composition databases. Am. J. Clin. Nutr. 2016, 104 (Suppl. S3), 868s–876s.
[CrossRef] [PubMed]
Andrews, K.W.; Roseland, J.M.; Gusev, P.A.; Palachuvattil, J.; Dang, P.T.; Savarala, S.; Han, F.; Pehrsson, P.R.;
Douglass, L.W.; Dwyer, J.T.; et al. Analytical ingredient content and variability of adult multivitamin/mineral
products: National estimates for the Dietary Supplement Ingredient Database. Am. J. Clin. Nutr. 2017, 105,
526–539. [CrossRef] [PubMed]
Nutrients 2018, 10, 100
15 of 20
Long, S.E.; Catron, B.L.; Boggs, A.S.; Tai, S.S.; Wise, S.A. Development of Standard Reference Materials to
support assessment of iodine status for nutritional and public health purposes. Am. J. Clin. Nutr. 2016, 104
(Suppl. S3), 902s–906s. [CrossRef] [PubMed]
Sharpless, K.E.; Lippa, K.A.; Duewer, D.L.; Rukhin, A.L. The ABCs of Using Standard Reference Materials in the
Analysis of Foods and Dietary Supplements: A Practical Guide; National Institute of Standards and Technology:
Gaithersburg, MD, USA, 2014.
Food and Agriculture Organization of the United Nations. International Network of Food Data Systems
(INFOODS)—International Food Composition Table/Database Directory. Available online: http://www.fao.
org/infoods/infoods/tables-and-databases/en/ (accessed on 7 November 2017).
International Life Sciences Institute Research Foundation (ILSI). World Nutrient Databases for Dietary
Studies. Available online: (accessed on 20 September 2017).
Global Fortification Data Exchange. Map: Count of Nutrients In Fortification Standards. Available online: (accessed on 19 December 2017).
Brantsæter, A.L.; Abel, M.H.; Haugen, M.; Meltzer, H.M. Risk of suboptimal iodine intake in pregnant
Norwegian women. Nutrients 2013, 5, 424–440. [CrossRef] [PubMed]
Haugen, M.; Brantsaeter, A.L.; Alexander, J.; Meltzer, H.M. Dietary supplements contribute substantially to
the total nutrient intake in pregnant Norwegian women. Ann. Nutr. Metab. 2008, 52, 272–280. [CrossRef]
Henjum, S.; Lilleengen, A.M.; Aakre, I.; Dudareva, A.; Gjengedal, E.L.F.; Meltzer, H.M.; Brantsaeter, A.L.
Suboptimal iodine concentration in breastmilk and inadequate iodine intake among lactating women in
Norway. Nutrients 2017, 9, 643. [CrossRef] [PubMed]
Andersen, S.L.; Sorensen, L.K.; Krejbjerg, A.; Moller, M.; Laurberg, P. Challenges in the evaluation of urinary
iodine status in pregnancy: The importance of iodine supplement intake and time of sampling. Eur. Thyroid J.
2014, 3, 179–188. [CrossRef] [PubMed]
Tetens, I.; Biltoft-Jensen, A.; Spagner, C.; Christensen, T.; Gille, M.B.; Bugel, S.; Banke Rasmussen, L. Intake of
micronutrients among Danish adult users and non-users of dietary supplements. Food Nutr. Res. 2011, 55.
[CrossRef] [PubMed]
Katagiri, R.; Yuan, X.; Kobayashi, S.; Sasaki, S. Effect of excess iodine intake on thyroid diseases in different
populations: A systematic review and meta-analyses including observational studies. PLoS ONE 2017, 12,
e0173722. [CrossRef] [PubMed]
United Nations International Children’s Emergency Fund (UNICEF). ARMENIA Prevention of Iodine
Deficiencies Disorders 2005 Annual Progress Report. Available online:
Pdach758.pdf (accessed on 6 November 2017).
Food Standards Australia New Zealand. Australian User Guide Mandatory Iodine Fortification
Implementing the Requirements of Mandatory Fortification with Iodised Salt under Standard 2.1.1—Cereals
and Cereal Products. Available online:
(accessed on 29 September 2017).
World Health Organization (WHO). Comparative Analysis of Progress on the Elimination of Iodine Deficiency
Disorders; WHO: Copenhagan, Denmark, 2000.
World Health Organization (WHO). Iodine Deficiency in Europe: A Continuing Public Health Problem; WHO:
Geneva, Switzerland, 2007.
Parman, S.; Ministry of Health Malaysia. Malayia. Available online:
documents/docs/maa.pdf (accessed on 6 November 2017).
Purves, H.D. The aetiology and prophylaxis of endemic goitre and cretinism. The New Zealand experience.
N. Z. Med. J. 1974, 80, 477–479. [PubMed]
Assey, V.D.; Peterson, S.; Kimboka, S.; Ngemera, D.; Mgoba, C.; Ruhiye, D.M.; Ndossi, G.D.; Greiner, T.;
Tylleskar, T. Tanzania national survey on iodine deficiency: Impact after twelve years of salt iodation.
BMC Public Health 2009, 9, 319. [CrossRef] [PubMed]
Doggui, R.; El Ati-Hellal, M.; Traissac, P.; Lahmar, L.; El Ati, J. Adequacy assessment of a universal salt
iodization program two decades after its implementation: A national cross-sectional study of iodine status
among school-age children in Tunisia. Nutrients 2017, 9, 6. [CrossRef] [PubMed]
Nutrients 2018, 10, 100
16 of 20
Food Standards Australia New Zealand.
Proposal P1003 Mandatory Iodine Fortification for
Australia Assessment Report. Available online:
documents/P1003%20Mandatory%20Iodine%20fortification%20Aust%20AR%20FINAL.pdf (accessed on
30 October 2017).
Food Standards Australia New Zealand. Final Assessment Report, Proposal P230, Consideration of
Mandatory Fortification with Iodine for New Zealand. Available online: http://www.foodstandards. (accessed on 7 November 2017).
Muzzo, S.; Pretell, E. IDD Newsletter—Iodine Excess in Chile. Available online:
newsletter/idd_nl_feb09_chile.pdf (accessed on 6 November 2017).
Sun, D.; Codling, K.; Chang, S.; Zhang, S.; Shen, H.; Su, X.; Chen, Z.; Scherpbier, R.W.; Yan, J. Eliminating
iodine deficiency in China: Achievements, challenges and global implications. Nutrients 2017, 9, 361.
[CrossRef] [PubMed]
Ministry of Health Republic of Costa Rica; United Nations Children’s Fund (UNICEF). Iodizing Salt A Health
Policy, The Costa Rican Experience; UNICEF: San José, Costa Rica, 2013.
National Iodine Deficiency Disorders Control Program (NIDDCP). Salt Iodiasation Program in
INDIA. Available online: (accessed on
30 October 2017).
Sebotsa, M.L.; Dannhauser, A.; Jooste, P.L.; Joubert, G. Assessment of the sustainability of the
iodine-deficiency disorders control program in Lesotho. Food Nutr. Bull. 2007, 28, 337–347. [CrossRef]
Jooste, P. IDD Newsletter—Mozambique Redoubles Its Salt Iodization Efforts. Available online: http:
// (accessed on 7 November 2017).
Gelal, B.; Baral, N. Moving Toward the Sustainable Ellimination of IDD in Nepal. Available online: http:
// (accessed on 7 November 2017).
Temple, V.J. IDD Newsletter—Progress Towards Elimination of IDD in Papua New Guinea. Available online: (accessed on 7 November 2017).
Kazakh Academy of Nutrition (KAN). Serbia Vignette. Available online:
serbia_vignette.pdf (accessed on 2 October 2017).
Codling, K.; Rudert, C.; Begin, F.; Pena-Rosas, J.P. The legislative framework for salt iodization in Asia and
the Pacific and its impact on programme implementation. Public Health Nutr. 2017, 20, 3008–3018. [CrossRef]
Jooste, P.L.; Weight, M.J.; Lombard, C.J. Iodine concentration in household salt in South Africa. Bull. World
Health Organ. 2001, 79, 534–540. [PubMed]
Ministry of Public Health Thailand. Notification of Ministry of Public Health No. 153 [B.E. 2537(1994)]
Re: Iodized Salt. Available online:
%20333%20Edible%20Salt.pdf (accessed on 3 October 2017).
Uganda National Bureau of Standards. Revision of the Salt Iodisation Regulations and Standards for
Iodised Salt in Uganda. Final Report. Available online:
(accessed on 30 October 2017).
United Nations International Children’s Emergency Fund (UNICEF). Salt Iodisation in Viet Nam: Learning
from the Past and Building Back Better. Available online:
Eng_E-mail_version.pdf (accessed on 30 October 2017).
Leung, A.M.; Braverman, L.E.; Pearce, E.N. History of U.S. iodine fortification and supplementation.
Nutrients 2012, 4, 1740–1746. [CrossRef] [PubMed]
Greenfield, H.; Southgate, D.A.T. Food Composition Data: Production, Management and Use, 2nd ed.; Food and
Agriculture Organization of the United Nations: Rome, Italy, 2003.
Carriquiry, A.L.; Spungen, J.H.; Murphy, S.P.; Pehrsson, P.R.; Dwyer, J.T.; Juan, W.; Wirtz, M.S. Variation
in the iodine concentrations of foods: Considerations for dietary assessment. Am. J. Clin. Nutr. 2016, 104
(Suppl. S3), 877s–887s. [CrossRef] [PubMed]
Fuge, R.; Johnson, C.C. Iodine and human health, the role of environmental geochemistry and diet: A review.
Appl. Geochem. 2015, 63, 282–302. [CrossRef]
Nutrients 2018, 10, 100
17 of 20
Chen, W.; Li, X.; Wu, Y.; Bian, J.; Shen, J.; Jiang, W.; Tan, L.; Wang, X.; Wang, W.; Pearce, E.N.; et al.
Associations between iodine intake, thyroid volume, and goiter rate in school-aged Chinese children from
areas with high iodine drinking water concentrations. Am. J. Clin. Nutr. 2017, 105, 228–233. [CrossRef]
Ovadia, Y.S.; Gefel, D.; Aharoni, D.; Turkot, S.; Fytlovich, S.; Troen, A.M. Can desalinated seawater contribute
to iodine-deficiency disorders? An observation and hypothesis. Public Health Nutr. 2016, 19, 2808–2817.
[CrossRef] [PubMed]
United Nations Children’s Fund. Sustainable Elimination of Iodine Deficiency: Progress Since the 1990
World Summit for Children. Available online:
Elimination_of_Iodine_Deficiency.pdf (accessed on 10 October 2017).
World Health Organization (WHO). Fortification of Food-grade Salt with Iodine for the Prevention and
Control of Iodine Deficiency Disorders—Guideline. Available online:
publications/guidelines/fortification_foodgrade_saltwithiodine/en/ (accessed on 10 October 2017).
Dasgupta, P.K.; Liu, Y.; Dyke, J.V. Iodine nutrition: Iodine content of iodized salt in the United States.
Environ. Sci. Technol. 2008, 42, 1315–1323. [CrossRef] [PubMed]
National Academy of Science. The relation of selected trace elements to health and disease. In Geochemistry
and the Environment; National Academy of Science: Washington, DC, USA, 1974; Volume 1.
US DHHS Agency for Toxic Substances and Disease Registry (ATSDR). Toxicological Profile for Iodine; ATSDR:
Atlanta, GA, USA, 2004.
United States Nuclear Regulatory Commission Division of Safeguards. A Dynamic Model of the Global Iodine
Cycle for the Estimation of Dose to the World Population from Releases of Iodine-129 to the Environment; USNRC:
Rockville, MD, USA, 1979.
Katagiri, R.; Asakura, K.; Sasaki, S.; Hirota, N.; Notsu, A.; Miura, A.; Todoriki, H.; Fukui, M.; Date, C.
Estimation of habitual iodine intake in Japanese adults using 16 d diet records over four seasons with a
newly developed food composition database for iodine. Br. J. Nutr. 2015, 114, 624–634. [CrossRef] [PubMed]
Bouga, M.; Combet, E. Emergence of seaweed and seaweed-containing foods in the UK: Focus on labeling,
iodine content, toxicity and nutrition. Foods 2015, 4, 240–253. [CrossRef] [PubMed]
Sisasou, E.; Willey, N. Inter-taxa differences in iodine uptake by plants: Implications for food quality and
contamination. Agronomy 2015, 5, 537–554. [CrossRef]
USDA APHIS National Animal Health Monitoring System. Dairy 2014 Milk Quality, Milking Procedures,
and Mastitis on U.S. Dairies, 2014. Available online:
dairy/downloads/dairy14/Dairy14_dr_Mastitis.pdf (accessed on 24 October 2017).
Wenlock, R.W.; Buss, D.H.; Moxon, R.E.; Bunton, N.G. Trace nutrients. 4. Iodine in British food. Br. J. Nutr.
1982, 47, 381–390. [CrossRef] [PubMed]
Ershow, A.G.; Goodman, G.; Coates, P.M.; Swanson, C.A. Research needs for assessing iodine intake, iodine
status, and the effects of maternal iodine supplementation. Am. J. Clin. Nutr. 2016, 104 (Suppl. S3), 941s–949s.
[CrossRef] [PubMed]
USDA Agricultural Research Service Nutrient Data Laboratory. USDA Special Interest Databases on
Flavonoids. Available online:
(accessed on 30 October 2017).
Patterson, K.Y.; Bhagwat, S.A.; Williams, J.R.; Howe, J.C.; Holden, J.M. USDA Database for the Choline
Content of Common Foods Release Two. Available online:
80400525/Data/Choline/Choln02.pdf (accessed on 6 November 2017).
Haytowitz, D.B.; Lemar, L.E.; Pehrsson, P.R. USDA’s Nutrient Databank System—A tool for handling data
from diverse sources. J. Food Compost. Anal. 2009, 22, 433–441. [CrossRef]
US Food and Drug Administration. Total Diet Study. Available online:
FoodScienceResearch/TotalDietStudy/default.htm (accessed on 9 November 2017).
Trainer, D.; Pehrsson, P.R.; Haytowitz, D.B.; Holden, J.M.; Phillips, K.M.; Rasor, A.S.; Conley, N.A.
Development of sample handling procedures for foods under USDA’s National Food and Nutrient Analysis
Program. J. Food Compost. Anal. 2010, 23, 843–851. [CrossRef] [PubMed]
Nutrients 2018, 10, 100
18 of 20
Haytowitz, D.B.; Pehrsson, P.R. USDA’s National Food and Nutrient Analysis Program (NFNAP) produces
high-quality data for USDA food composition databases: Two decades of collaboration. Food Chem. 2018,
238, 134–138. [CrossRef] [PubMed]
Patterson, K.Y.; Pehrsson, P.R.; USDA-ARS Beltsville Human Nutrition Research Center, Nutrient Data
Laboratory, Beltsville, MD, USA. Personal communication, 2017.
Fulgoni, V.L., III; Keast, D.R.; Bailey, R.L.; Dwyer, J. Foods, fortificants, and supplements: Where do
Americans get their nutrients? J. Nutr. 2011, 141, 1847–1854. [CrossRef] [PubMed]
Kang, M.; Kim, D.W.; Lee, H.; Lee, Y.J.; Jung, H.J.; Paik, H.Y.; Song, Y.J. The nutrition contribution of dietary
supplements on total nutrient intake in children and adolescents. Eur. J. Clin. Nutr. 2016, 70, 257–261.
[CrossRef] [PubMed]
Matulka, R.A. Dietary Supplements in the U.S. and Abroad:
Similarities and Differences.
Available online: (accessed on 2 October 2017).
US Food and Drug Administration. What Is a Dietary Supplement? Available online: https://www.fda.
gov/aboutfda/transparency/basics/ucm195635.htm (accessed on 29 September 2017).
Skeie, G.; Braaten, T.; Hjartaker, A.; Lentjes, M.; Amiano, P.; Jakszyn, P.; Pala, V.; Palanca, A.; Niekerk, E.M.;
Verhagen, H.; et al. Use of dietary supplements in the European Prospective Investigation into Cancer and
Nutrition calibration study. Eur. J. Clin. Nutr. 2009, 63 (Suppl. S4), 226s–238s. [CrossRef] [PubMed]
Liu, F.X.; Salmon, J. Comparison of herbal medicines regulation between China, Germany, and the United
States. Integr. Med. 2010, 9, 42–49.
World Health Organization (WHO). National Policy on Traditional Medicine and Regulation of Herbal
Medicines—Report of a WHO Global Survey. Available online:
Js7916e/9.4.html (accessed on 1 October 2017).
Health Canada. About Natural Health Product Regulation in Canada. Available online: https://www.
(accessed on 1 October 2017).
National Institute for Public Health and the Environment (RIVM). Dutch Dietary Supplement Database (NES).
Available online:
Dutch_Dietary_Supplement_Database (accessed on 29 September 2017).
Verkaik-Kloosterman, J.; Buurma-Rethans, E.J.M.; Dekkers, A.L.M.; van Rossum, C.T.M. Decreased, but
still sufficient, iodine intake of children and adults in the Netherlands. Br. J.Nutr. 2017, 117, 1020–1031.
[CrossRef] [PubMed]
Food Standards Australia New Zealand. Dietary Supplement Nutrient Database. Available online: (accessed on
1 October 2017).
Lentjes, M.A.; Bhaniani, A.; Mulligan, A.A.; Khaw, K.T.; Welch, A.A. Developing a database of vitamin and
mineral supplements (ViMiS) for the Norfolk arm of the European Prospective Investigation into Cancer
(EPIC-Norfolk). Public Health Nutr. 2011, 14, 459–471. [CrossRef] [PubMed]
Dwyer, J.T.; Picciano, M.F.; Betz, J.M.; Fisher, K.D.; Saldanha, L.G.; Yetley, E.A.; Coates, P.M.; Milner, J.A.;
Whitted, J.; Burt, V.; et al. Progress in developing analytical and label-based dietary supplement databases at
the NIH Office of Dietary Supplements. J. Food Compost. Anal. 2008, 21, S83–S93. [CrossRef] [PubMed]
Dwyer, J.T.; Coates, P.M.; Smith, M. Challenges and resources in dietary supplement research. Nutrients 2018,
10, 41. [CrossRef] [PubMed]
Gahche, J.J.; Bailey, R.L.; Mirel, L.B.; Dwyer, J.T. The prevalence of using iodine-containing supplements is
low among reproductive-age women, NHANES 1999–2006. J. Nutr. 2013, 143, 872–877. [CrossRef] [PubMed]
US Food and Drug Administration. Nutrition Labeling of Dietary Supplements. e-CFR. 21CFR101.36.
Available online:
true&node=se21.2.101_136&rgn=div8 (accessed on 29 September 2017).
Turk, G.C.; Sharpless, K.E.; Cleveland, D.; Jongsma, C.; Mackey, E.A.; Marlow, A.F.; Oflaz, R.; Paul, R.L.;
Sieber, J.R.; Thompson, R.Q.; et al. Certification of elements in and use of standard reference material 3280
multivitamin/multielement tablets. J. AOAC Int. 2013, 96, 1281–1287. [CrossRef] [PubMed]
Nutrients 2018, 10, 100
19 of 20
USDA Agricultural Research Service; US DHHS NIH Office of Dietary Supplements. Dietary Supplement
Ingredient Database (DSID); Release 4.0. Available online: https://dietarysupplementdatabase.usda.nih.
gov/ (accessed on 23 October 2017).
Saldanha, L.G.; Dwyer, J.T.; Andrews, K.W.; Brown, L.L.; Costello, R.B.; Ershow, A.G.; Gusev, P.A.; Hardy, C.J.;
Pehrsson, P.R. Is nutrient content and other label information for prescription prenatal supplements different
from nonprescription products? J. Acad. Nutr. Diet. 2017, 117, 1429–1436. [CrossRef] [PubMed]
Lee, K.W.; Shin, D.; Cho, M.S.; Song, W.O. Food group intakes as determinants of iodine status among US
adult population. Nutrients 2016, 8, 325. [CrossRef] [PubMed]
Rogan, W.J.; Paulson, J.A.; Baum, C.; Brock-Utne, A.C.; Brumberg, H.L.; Campbell, C.C.; Lanphear, B.P.;
Lowry, J.A.; Osterhoudt, K.C.; Sandel, M.T.; et al. Iodine deficiency, pollutant chemicals, and the thyroid:
New information on an old problem. Pediatrics 2014, 133, 1163–1166. [PubMed]
De Groot, L.; Abalovich, M.; Alexander, E.K.; Amino, N.; Barbour, L.; Cobin, R.H.; Eastman, C.J.; Lazarus, J.H.;
Luton, D.; Mandel, S.J.; et al. Management of thyroid dysfunction during pregnancy and postpartum: An
Endocrine Society clinical practice guideline. J. Clin. Endocrinol. Metab. 2012, 97, 2543–2565. [CrossRef]
Obican, S.G.; Jahnke, G.D.; Soldin, O.P.; Scialli, A.R. Teratology public affairs committee position paper:
Iodine deficiency in pregnancy. Birth Defects Res. A Clin. Mol. Teratol. 2012, 94, 677–682. [CrossRef] [PubMed]
Alexander, E.K.; Pearce, E.N.; Brent, G.A.; Brown, R.S.; Chen, H.; Dosiou, C.; Grobman, W.A.; Laurberg, P.;
Lazarus, J.H.; Mandel, S.J.; et al. 2017 Guidelines of the American Thyroid Association for the Diagnosis
and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid 2017, 27, 315–389.
[CrossRef] [PubMed]
Australian National Health and Medical Research Council (NHMRC). NHMRC Public Statement: Iodine
Supplementation for Pregnant and Breastfeeding Women. Available online:
_files_nhmrc/publications/attachments/new45_statement.pdf (accessed on 6 November 2017).
New Zealand Ministry of Health. Iodine. Available online:
preventative-health-wellness/nutrition/iodine (accessed on 10 October 2017).
Reynolds, A.N.; Skeaff, S.A. Maternal adherence with recommendations for folic acid and iodine
supplements: A cross-sectional survey. Aust. N. Z. J. Obstet. Gynaecol. 2017. [CrossRef] [PubMed]
New Zealand Institute for Plant & Food Research Limited; Ministry of Health (New Zealand). The Concise
New Zealand Food Composition Tables, 12th ed.; New Zealand Institute for Plant & Food Research Limited;
Ministry of Health (New Zealand): Auckland, New Zealand, 2016. Available online: http://www. (accessed on 10 October 2017).
Ministry for Primary Industries. Update Report on the Dietary Iodine Intake of New Zealand Children
Following Fortification of Bread with Iodine. Available online:
(accessed on 20 December 2017).
Zmitek, K.; Pravst, I. Iodisation of salt in Slovenia: Increased availability of non-iodised salt in the food
supply. Nutrients 2016, 8, 434. [CrossRef] [PubMed]
Limbert, E.; Prazeres, S.; Sao Pedro, M.; Madureira, D.; Miranda, A.; Ribeiro, M.; Jacome de Castro, J.;
Carrilho, F.; Oliveira, M.J.; Reguengo, H.; et al. Iodine intake in Portuguese pregnant women: Results of a
countrywide study. Eur. J. Endocrinol. 2010, 163, 631–635. [CrossRef] [PubMed]
Ovadia, Y.S.; Arbelle, J.E.; Gefel, D.; Brik, H.; Wolf, T.; Nadler, V.; Hunziker, S.; Zimmermann, M.B.;
Troen, A.M. First Israeli national iodine survey demonstrates iodine deficiency among school-aged children
and pregnant women. Thyroid 2017, 27, 1083–1091. [CrossRef] [PubMed]
Costa Leite, J.; Keating, E.; Pestana, D.; Cruz Fernandes, V.; Maia, M.L.; Norberto, S.; Pinto, E.;
Moreira-Rosario, A.; Sintra, D.; Moreira, B.; et al. Iodine status and iodised salt consumption in Portuguese
school-aged children: The Iogeneration Study. Nutrients 2017, 9, 458. [CrossRef] [PubMed]
Pearce, E.N.; Caldwell, K.L. Urinary iodine, thyroid function, and thyroglobulin as biomarkers of iodine
status. Am. J. Clin. Nutr. 2016, 104 (Suppl. S3), 898s–901s. [CrossRef] [PubMed]
Tayie, F.A.; Jourdan, K. Hypertension, dietary salt restriction, and iodine deficiency among adults.
Am. J. Hypertens. 2010, 23, 1095–1102. [CrossRef] [PubMed]
Appleby, P.N.; Thorogood, M.; Mann, J.I.; Key, T.J. The Oxford Vegetarian Study: An overview.
Am. J. Clin. Nutr. 1999, 70, 525S–531S. [PubMed]
Nutrients 2018, 10, 100
20 of 20
117. Leung, A.M.; Lamar, A.; He, X.; Braverman, L.E.; Pearce, E.N. Iodine status and thyroid function of
Boston-area vegetarians and vegans. J. Clin. Endocrinol. Metab. 2011, 96, E1303–E1307. [CrossRef] [PubMed]
118. Schupbach, R.; Wegmuller, R.; Berguerand, C.; Bui, M.; Herter-Aeberli, I. Micronutrient status and intake in
omnivores, vegetarians and vegans in Switzerland. Eur. J. Nutr. 2017, 56, 283–293. [CrossRef] [PubMed]
119. Manousou, S.; Stal, M.; Larsson, C.; Mellberg, C.; Lindahl, B.; Eggertsen, R.; Hulthen, L.; Olsson, T.;
Ryberg, M.; Sandberg, S.; et al. A Paleolithic-type diet results in iodine deficiency: A 2-year randomized trial
in postmenopausal obese women. Eur. J. Clin. Nutr. 2017. [CrossRef] [PubMed]
120. Bath, S.C.; Hill, S.; Infante, H.G.; Elghul, S.; Nezianya, C.J.; Rayman, M.P. Iodine concentration of
milk-alternative drinks available in the UK in comparison with cows’ milk. Br. J. Nutr. 2017, 118, 525–532.
[CrossRef] [PubMed]
121. Skalnaya, M.G.; Skalny, A.V.; Tinkov, A.A. TEMA-16 Abstracts. J. Trace Elem. Med. Biol. 2017, 41 (Suppl. S1),
122. Sawka, A.M.; Ibrahim-Zada, I.; Galacgac, P.; Tsang, R.W.; Brierley, J.D.; Ezzat, S.; Goldstein, D.P. Dietary
iodine restriction in preparation for radioactive iodine treatment or scanning in well-differentiated thyroid
cancer: A systematic review. Thyroid 2010, 20, 1129–1138. [CrossRef] [PubMed]
123. Morris, L.F.; Wilder, M.S.; Waxman, A.D.; Braunstein, G.D. Reevaluation of the impact of a stringent
low-iodine diet on ablation rates in radioiodine treatment of thyroid carcinoma. Thyroid 2001, 11, 749–755.
[CrossRef] [PubMed]
124. Kim, H.K.; Lee, S.Y.; Lee, J.I.; Jang, H.W.; Kim, S.K.; Chung, H.S.; Tan, A.H.; Hur, K.Y.; Kim, J.H.; Chung, J.H.;
et al. Usefulness of iodine/creatinine ratio from spot-urine samples to evaluate the effectiveness of low-iodine
diet preparation for radioiodine therapy. Clin. Endocrinol. 2010, 73, 114–118. [CrossRef] [PubMed]
125. Kim, H.K.; Lee, S.Y.; Lee, J.I.; Jang, H.W.; Kim, S.K.; Chung, H.S.; Tan, A.H.; Hur, K.Y.; Kim, J.H.; Chung, J.H.;
et al. Daily urine iodine excretion while consuming a low-iodine diet in preparation for radioactive iodine
therapy in a high iodine intake area. Clin. Endocrinol. 2011, 75, 851–856. [CrossRef] [PubMed]
126. Li, J.H.; He, Z.H.; Bansal, V.; Hennessey, J.V. Low iodine diet in differentiated thyroid cancer: A review.
Clin. Endocrinol. 2016, 84, 3–12. [CrossRef] [PubMed]
127. Morsch, E.P.; Vanacor, R.; Furlanetto, T.W.; Schmid, H. Two weeks of a low-iodine diet are equivalent to 3
weeks for lowering urinary iodine and increasing thyroid radioactive iodine uptake. Thyroid 2011, 21, 61–67.
[CrossRef] [PubMed]
128. Gaitan, E. Goitrogens in food and water. Annu. Rev. Nutr. 1990, 10, 21–39. [CrossRef] [PubMed]
129. Bhagwat, S.; Haytowitz, D.B.; Holden, J.M. USDA Database for the Flavonoid Content of Selected Foods,
Release 3.1. Available online:
(accessed on 30 October 2017).
130. Abt, E.; Spungen, J.; Pouillot, R.; Gamalo-Siebers, M.; Wirtz, M. Update on dietary intake of perchlorate and
iodine from U.S. food and drug administration’s total diet study: 2008–2012. J. Expo. Sci. Environ. Epidemiol.
2018, 28, 21–30. [CrossRef] [PubMed]
131. Mortensen, M.E.; Birch, R.; Wong, L.Y.; Valentin-Blasini, L.; Boyle, E.B.; Caldwell, K.L.; Merrill, L.S.;
Moye, J., Jr.; Blount, B.C. Thyroid antagonists and thyroid indicators in U.S. pregnant women in the
Vanguard Study of the National Children’s Study. Environ. Res. 2016, 149, 179–188. [CrossRef] [PubMed]
132. Corey, L.M.; Bell, G.P.; Pleus, R.C. Exposure of the US population to nitrate, thiocyanate, perchlorate, and
iodine based on NHANES 2005–2014. Bull. Environ. Contam. Toxicol. 2017, 99, 83–88. [CrossRef] [PubMed]
133. Lee, K.W.; Cho, M.S.; Shin, D.; Song, W.O. Changes in iodine status among US adults, 2001–2012. Int. J. Food
Sci. Nutr. 2016, 67, 184–194. [CrossRef] [PubMed]
© 2018 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (