Iodine Policy in the United
States
Elizabeth N. Pearce, M.D., M.Sc.
Overview
• Dietary iodine requirements and
assessment of iodine sufficiency
• Current U.S. iodine nutrition status
• Sources of U.S. Dietary Iodine
• Iodine recommendations
Recommended Daily Dietary Iodine Intakes
U.S. Institute of Medicine
WHO, UNICEF, ICCIDD
µg/day
0-6 months (AI)
110
7-12 months (AI)
130
1-8 years
90
9-13 years
µg/day
0-5 years
90
120
6-12 years
120
>13 years
150
>12 years
150
Pregnancy
220
Pregnancy
250
Lactation
290
Lactation
250
- U.S. Institute of Medicine 2006
- WHO, UNICEF, ICCIDD 2007
Increased demand for thyroid hormone (↑ 50%),
requires an additional 50-100 μg iodine:
- Thyrotropic regulation by hCG
- Estrogen-mediated TBG increase
Increased Maternal Dietary Iodine Requirements
in Pregnancy
Placental Type 3 deiodinase
Iodide transferred to the fetus
(50-75 μg/day)
Increased
renal iodine
clearance
(↑ 30-50%)
Increased Dietary Iodine Requirements
in Lactation
• Normal lactating breast ducts
concentrate iodide (via sodium
iodide symporter), secreting it
into milk
Tazebay et al Nat Med 2000; 6:859-60
• Only source of iodine nutrition
for breastfed infants
Tolerable Upper Limits for Iodine Exposure
U.S. Institute of
Medicine
0-12 months
1-3 years
4-8 years
9-13 years
14-18 years
19-50 years
WHO, UNICEF,
ICCIDD
µg/day
unknown Infants
200
Pregnancy
300
Lactation
600
900
1,100
µg/day
180
500
500
- U.S. Institute of Medicine 2006
- WHO, UNICEF, ICCIDD 2007
Population Urinary Iodine Values and Iodine Nutrition
Median Urinary Iodine Corresponding Iodine
Concentration (μg/L)
Intake (μg/day)
Iodine
Nutrition
<20
<30
Severe
deficiency
20-49
30-74
Moderate
deficiency
50-99
75-149
Mild deficiency
100-199
150-299
Optimal
200-299
300-449
More than
adequate
>299
>449
Possible excess
For children < age 2, Urinary iodine ≥100 μg/L = sufficiency
WHO/ICCIDD/UNICEF, 2007
Urinary Iodine Values and Iodine
Nutrition in Pregnancy and Lactation
Population group
Non-pregnant
adults
Median Urinary Iodine
Concentration (μg/L)
Optimal
Excessive
100-199
>299
Pregnant Women
150-249
Lactating Women
≥100
≥500
WHO Public Health Nutr 2007
Overview
• Dietary iodine requirements and
assessment of iodine sufficiency
• Current U.S. iodine nutrition status
• Sources of U.S. Dietary Iodine
• Iodine recommendations
U.S. Goiter Belt (pre-1920s)
– 26 - 70% of children had goiter
Morton Salt, 1920s
Median Urine Iodine Concentration (μg/L)
Median U.S. Urinary Iodine Concentration
NHANES 1971-2004
400
350 320
300
250
200
150
145
168
160
164
144
Total
Males
Females
100
50
0
1971- 1988- 2001- 2003- 2007- 200974
94
02
04
08
10
Hollowell et al. JCEM 1998; 83:3401-8; Caldwell et al. Thyroid 2005;15:692-9; Caldwell et al.
Thyroid 2008;18:1207-14; Caldwell et al. Thyroid 2011;21:419-27; Caldwell et al, Thyroid 2013; 23:927-37
% of U.S. Population with Urinary Iodine
<50μg/L: NHANES I and NHANES III
Age (years)
JG Hollowell et al. J Clin Endocrinol Metab1998; 83:3401-8
Median urinary iodine concentration (UIC)
among pregnant women, NHANES
Median UIC μg/L with
95% CI
Median UIC in pregnancy 129 µg/L
2005-2010
Above requirement iodine intake
Adequate iodine intake
Insufficient iodine intake
NHANES Survey
Hollowell et al, JCEM 1998; 83:3401-8; Caldwell et al. Thyroid 2005;15:692-9; Caldwell et al. Thyroid
2008;18:1207-14; Caldwell et al. Thyroid 2011;21:419-27; Caldwell et al. Thyroid 2013;23:927-37
Median Urinary Iodine (mg/L)
Urine Iodine in a Sample of
100 Pregnant Women Living in Boston
500
438
400
300
230
200
100
150 mg/L
~220 mg/day
dietary intake
(RDA for
pregnancy)
149
96
52
0
1
2
3
4
5
Urinary Iodine by Quintiles
EN Pearce et al. Thyroid 2004; 14:327-8
Iodine Status of Lactating BostonArea Women and their Infants
Iodine Concentration in µg/L
median (interquartile range)
Breast Milk
45.6 (4.3-1080)
Maternal Urine
101.9 (27-570)
Infant Urine
197.5 (40-785)
64 mother-infant pairs
Infants age 1-3 months
AM Leung et al. Thyroid 2012;22:938-43.
US Infant Formulae Iodine Content
U.S.: allowable 5-75 µg/100 kcal
Pearce EN et al. J Clin Endocrinol Metab 2007;92:1673-7
UIC (μg/L)
Urinary Iodine Concentrations in Breast
and Bottle-Fed Infants from the Boston Area
n=44
n=39
n=10
JH Gordon et al. Thyroid 2014;1309-13
Median UIC μg/L with 95% CI
Median urinary iodine concentration among
children age 6-11, NHANES
Excessive iodine intake
Above requirement
iodine intake
Adequate iodine intake
Insufficient iodine intake
NHANES Survey
Hollowell et al, JCEM 1998; 83:3401-8; Caldwell et al. Thyroid 2005;15:692-9; Caldwell et al. Thyroid
2008;18:1207-14; Caldwell et al. Thyroid 2011;21:419-27; Caldwell et al. Thyroid 2013;23:927-37
Overview
• Dietary iodine requirements and
assessment of iodine sufficiency
• Current U.S. iodine nutrition status
• Sources of U.S. Dietary Iodine
• Iodine recommendations
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% Daily iodine Intake
Median Iodine Content of Adult* Diets
2003-2004 FDA Total Diet Study
*Women age 25-30
CW Murray et al. J Expo Sci Environmen Epidemiol 2008;18:571-80.
Salt in the U.S. Diet
6% While
eating
5% While
cooking
• ~77% of salt in U.S diet from
restaurant/processed food,
usually not iodized
•~11% table salt added at the
table or in cooking, 53% of table
salt in U.S. is iodized at 60-100
ppm
12% Naturally
occurring
77%
Restaurant and
processed
foods
• ~50% of reproductive age
women never/rarely use table
salt
Mattes & Donnelly. J Am Coll Nutr 1991;10(4):383-93.
Maalouf J et al. Nutrients 2015;1691-5
Bread Iodine Content
• Iodate dough conditioners used starting
1940s. Use 1970s-1990s.
• Boston-area supermarkets 2001-2002:
– 20 brands measured
– 3 breads >313 μg I/slice
– Others 2.2-54 μg I/slice (mean 10 μg/slice)
• Package labels inaccurate
EN Pearce et al. J Clin Endocrinol Metab 2004; 89:3421-4
Mean Iodine Content of New England
Cows’ Milk2D Graph
by 2Season
μg I per 250 ml (~1 cup)
160
n = 18 brands
p <0.0005
140
120
116
100
91
80
60
40
20
0
0
1
Winter
2
Summer
3
EN Pearce et al. J Clin Endocrinol Metab 2004; 89:3421-4
Iodine Sources in U.S.
Cows’ Milk
• Cattle feed
– Cows’ milk iodine content increased 300-500%
1965-1980 due to increased I in cattle feed
– Organic iodine ethylenediamine dihydroiodine
(EDDI) content of cattle feed limited 1986 to
10mg/cow/day
• Iodophor disinfectant in teat dip/udder wash
– Up to 1% available iodine
EN Pearce et al. J Clin Endocrinol Metab 2004; 89:3421-4
Median Urinary Iodine Levels in
U.S. Vegetarians and Vegans
Optimal
iodine
intake
(WHO)
164
200
150
147
100
(µg/L)
50
78.5
Median
U.S.
urinary
iodine
0
vegans
n=62
vegetarians
n=78
AM Leung et al. J Clin Endocrinol Metab 2011;96:E1303-7.
Overview
• Dietary iodine requirements and
assessment of iodine sufficiency
• Current U.S. iodine nutrition status
• Sources of U.S. Dietary Iodine
• Iodine recommendations
U.S. Guidelines
Women who are planning to be
pregnant or are pregnant or
breastfeeding should
supplement their diet with a daily
oral supplement that contains 150
µg of iodine.
• A Stagnaro-Green et al. Thyroid 2011;21:1081-125
• L De Groot L et al. J Clin Endocrinol Metab
2012;97:2543-65
• SG Obican et al. Birth Defects Res A Clin Mol Teratol
2012;94: 677-682
• AAP Council on Environmental Health. Pediatrics
2014;133:1163-6
Percentage of Reproductive Age U.S. Women
Reporting Supplement Use Within 30 Days
Based on NHANES 2001-2006
76.9
67.8
Any Supplement
43.4
20.3
14.5
Supplement
with Iodine
La
ct
at
in
g
na
nt
re
g
P
pr
eg
na
nt
20.2
N
on
%
90
80
70
60
50
40
30
20
10
0
Pregnant
n=4322
n=983
n=143
CO Gregory et al. Thyroid 2009;19:1019-20
Proportion of U.S.
Prenatal Multivitamins
Containing Iodine
69%
28%
(n=87)
contain
iodine
(n=27)
contain
iodine
Non-prescription
prenatal multivitamins
(n = 127)
Prescription prenatal
multivitamins
(n = 96)
AM Leung et al. N Engl J Med 2009;360:939-40
January 27, 2015—Dietary supplement manufacturers
should include a daily serving of at least 150 mcg of
iodine in all multivitamin/mineral supplements
intended for pregnant and lactating women in the
U.S., the Council for Responsible Nutrition (CRN)
advises in guidelines for industry released today.
CRN recommends that dietary supplement companies
comply within twelve months.
Conclusions
• Overall dietary iodine intake is currently
sufficient in the U.S.
• However, there are concerns about mild
iodine deficiency among women during
pregnancy and lactation
– Recommend iodine-containing prenatal
multivitamin
• Further monitoring is needed