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Growing Brains Lack Iodine
Alarming maternal deficiency rates prompt calls to ensure intake via supplements or seafood

05/28/2013 By Craig Weatherby
Six years ago, a landmark study found that kids gained brain power when pregnant mothers ate more fish than the 12 oz. per week that U.S. FDA/EPA guidelines recommend.
The children of mothers who ate more than 12 oz. of fish per week displayed greater physical dexterity and scored higher on intelligence, social, and verbal tests, compared with their peers.
As we wrote then, “… the results may finally end overblown fears that could conceivably lead mothers to under-consume fish, and thereby put their babies at risk of suboptimal brain development.”
That investigation included was conducted as part of the Avon Longitudinal Study of Parents and Children (ALSPAC), and involved almost 9,000 British families.
Recommended Dietary
Allowances (RDAs) for Iodine
Note: A microgram (mcg) is one-millionth of a gram, and one-thousandth of a milligram (mg).
Ages 1 to 8 – 90mcg
Ages 9 to 13 – 120mcg
Ages 14 and over 150mcg
Pregnant women* – 220mcg
Nursing women – 290mcg

*The World Health Organization, UNICEF, and the International Council for the Control of Iodine Deficiency Disorders (ICCIDD) recommend 250 mcg per day for pregnant women.

The authors presumed that omega-3 fatty acids were the major factor in the brain gains observed among children born to mothers who ate ample amounts of fish (Hibbeln JR et al. 2007).
But a new analysis of data collected from the ALSPAC study – published in the major British medical journal Lancet – suggests that another fishy nutrient may have played a major role.
Iodine: The overlooked brain-development nutrient
Human fetuses need iodine to produce thyroid hormone, which in turn is essential for brain development … particularly in the first trimester of pregnancy.
Although seafood is the richest natural source, Americans get most of their iodine from milk, milk products, multivitamin-mineral supplements, or iodized salt added to foods.
Processed foods almost never contain iodized salt … and oddly, a UK study found that organic milk averaged 42 percent less iodine compared with conventional milk, with regional variations (Bath SC et al. 2012).
Most Americans get adequate amounts of dietary iodine, but two groups are more likely to fall short:
  • People who do not use iodized salt.
  • Pregnant women often do not get quite enough iodine.
To provide enough iodine for their baby, pregnant women need about 50 percent more iodine than other women.
However, very few studies have probed the effect of mild-to-moderate iodine deficiency during pregnancy on children's cognitive development.
Iodine in seafood
Seafood is the richest source of iodine,though levels can vary widely by region and seasons.
These are the average iodine levels in some common fish and shellfish, per 3 oz. serving:
Oysters  – 137mcg
Mussels – 110mcg
Prawns – 110mcg
Cod – 99mcg
Salmon – 60mcg
Halibut – 44mcg
Mackerel – 40mcg
Shrimp – 35mcg
Sardines – 20mcg
Tuna – 17mcg
Recently, the documentation of mild-to-moderate iodine deficiency in some UK population groups – including pregnant women – prompted a study into its effects.
UK study finds iodine deficiency common ...
...and damaging to children's brain development
Last month, the results of a large study among British mothers and children appeared in the British medical journal Lancet.
Its outcomes confirmed two things:
  • Iodine deficiency during pregnancy is widespread.
  • Mothers' iodine deficiency adversely impacts their children's mental development.
The investigation comes from a group of researchers at the Universities of Surrey and Bristol, who analyzed maternal urine samples and child-development data from the ALSPAC study.
Led by Professor Margaret Rayman of the University of Surrey, the researchers measured the first-trimester iodine levels of 1,040 pregnant women.
Then, they divided the women into two groups:
  • Iodine-deficient (iodine-to-creatinine ratio of less than 150 μg/g)
  • Iodine-sufficient (iodine-to-creatinine ratio equal to or greater than 150 μg/g).
Alarmingly, more than two thirds (67 percent) of the women proved to be iodine-deficient.
The UK team then measured children's mental development by testing their IQ at age eight and their reading ability at age nine.
Alarmingly, the results showed that children of women in the iodine-deficient group were significantly more likely to have low verbal IQ, reading accuracy, and reading comprehension scores.
This concerning outcome was calculated after they accounted for other factors likely to affect the test scores … including parental education levels, maternal omega-3 intakes, and breast-feeding.
Critically, the impact of iodine deficiency was confirmed by the fact that the mothers' iodine levels correlated to their children's IQ and reading scores.
In other words, the mothers of children who scored lowest the IQ and reading tests had low iodine levels, while the mothers of high-scoring kids had high iodine levels.
According to Professor Rayman, “Our results clearly show the importance of adequate iodine status during early pregnancy, and emphasize the risk that iodine deficiency can pose to the developing infant, even in a country classified as only mildly iodine deficient.” (UB 2013)
Professor Jean Golding OBE – a co-author and the ALSPAC project founder – added a key point: “This study provides further strong evidence of the importance of eating iodine-rich foods like fish during pregnancy.” (UB 2013)
Commenting in Lancet on the study, Alex Stagnaro-Green of George Washington University, wrote that the findings “… should be regarded as a call to action to public health policy makers.” (Stagnaro-Green A, Pearce EN 2013)
To learn more about the roles of fish and omega-3s in child development, we recommend the University of North Dakota website Fish, Mercury, and Nutrition, the Omega-3s & Child Development and Mercury Issues sections of our news archive, and our Healthy Mom & Baby page.
  • ALSPAC Study Team. Accessed online at Feb 17, 2007.
  • Bath SC, Rayman MP. Iodine deficiency in the U.K.: an overlooked cause of impaired neurodevelopment? Proc Nutr Soc. 2013 May;72(2):226-35. doi: 10.1017/S0029665113001006.
  • Bath SC, Steer CD, Golding J, Emmett P, Rayman MP. 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 May 21. doi:pii: S0140-6736(13)60436-5. 10.1016/S0140-6736(13)60436-5. [Epub ahead of print]
  • Bath SC, Button S, Rayman MP. Iodine concentration of organic and conventional milk: implications for iodine intake. Br J Nutr. 2012 Apr;107(7):935-40. doi: 10.1017/S0007114511003059. Epub 2011 Jul 5.
  • Daniels JL, Longnecker MP, Rowland AS, Golding J; ALSPAC Study Team. University of Bristol Institute of Child Health. Fish intake during pregnancy and early cognitive development of offspring. Epidemiology. 2004 Jul;15(4):394-402.
  • Golding J, Pembrey M, Jones RALSPAC Study Team. ALSPAC: the Avon Longitudinal Study of Parents and Children. I. Study methodology. Paediatr Perinat Epidemiol 2001; 15: 74-87.
  • Hibbeln JR, Davis JM, Steer C, Emmett P, Rogers I, Williams C, Golding J. Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study. The Lancet 2007; 369:578-585.
  • Office of Dietary Supplements Health Professional Fact Sheet on Iodine. Accessed at
  • Springen K. Pregnant Women: Eat More Fish or Not? Newsweek. Accessed online Feb 17, 2007 at
  • Stagnaro-Green A, Pearce EN. Iodine and pregnancy: a call to action. Lancet. 2013 May 21. doi:pii: S0140-6736(13)60717-5. 10.1016/S0140-6736(13)60717-5. [Epub ahead of print]
  • University of Bristol (UB). Iodine deficiency during pregnancy adversely affects children's mental development. May 22, 2013. Accessed at

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