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Presenters focus on status, effects of iodine intake
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QUEBEC CITY — During a presentation here, speakers outlined the status of iodine nutrition in the United States and the United Kingdom, emphasizing the importance of understanding the impact of iodine intake on the thyroid.
“Overall, the median urinary iodine concentration for the general US population appears to be sufficient, but non-Hispanic black groups are significantly lower in urinary iodine levels throughout all age ranges in both the National Children’s Study and NHANES,” Kathleen Caldwell, PhD, of the CDC, said.
United States
“If we take a step back and look at children from NHANES 2005-2006 according to race/ethnicity, we see that non-Hispanic whites are at the upper end of having more than adequate levels, whereas significantly less non-Hispanic blacks are at an adequate level, and Mexican Americans are just slightly above adequate,” Caldwell said.
Researchers have also identified differences in race/ethnicity in the National Children’s Study (NCS) — one of the largest, long-term studies of children’s health and development, according to Caldwell. Similar to the NHANES data, non-Hispanic whites and all Hispanics had urine iodine levels of 179 mcg/L, but non-Hispanic blacks had a level of 132 mcg/L.
“One reason why this may be occurring is that non-Hispanic blacks are more likely to have perceived lactose intolerance that is not diagnosed by a physician, so it could be that non-Hispanic blacks are not consuming the same amount of dairy,” Caldwell said, noting that dairy products are a major source of iodine.
Additionally, she said that women have historically had lower iodine concentrations when compared with men — a trend that continues to exist. Data from 2005 to 2008 show that pregnant and non-pregnant women of childbearing age had a median iodine level of 133 mcg/L, with approximately 55% of women having levels below the accepted adequate level of 150 mcg/L. Results from the NCS including pregnant women, however, showed that only non-Hispanic blacks had a less than adequate urinary iodine concentration.
Iodine concentrations also appeared to vary across US regions, according to Caldwell, signaling the need for further investigation.
“We can use the data collected in this study to help influence the larger NCS main study visit protocols to help identify urinary iodine differences among region and race/ethnicity,” Caldwell said. “We need health promotion strategies to make sure consumers choose iodized salt when they do use salt at home based upon awareness of the need for iodine for normal development. We should also encourage individuals with perceived lactose intolerance to seek medical intervention.”
United Kingdom
Mark Vanderpump, MB, ChB, MD, FRCP, consultant physician and honorary senior lecturer in diabetes and endocrinology at the Royal Free Hampstead NHS Trust in London, also described the state of iodine nutrition in the United Kingdom, suggesting a shift in focus when developing strategies to improve iodine levels.
In a recent survey of schoolgirls, who were selected because they are a group at high risk for iodine deficiency, researchers found low to medium iodine concentrations, with results indicating that 70% of all schoolgirls were iodine deficient. In terms of milk intake, the data also showed that children who did not drink milk had the lowest iodine concentrations.
“In industrialized countries as you’re hearing, there are strong public health objectives aimed at lowering salt intake because it is clearly seen as a major contributor to hypertension in industrialized countries,” Vanderpump said. “In the U.K., we have almost no iodine in any salt. The majority is from processed foods and only about 10% of salt is added at the table at home.”
He also noted that industrialized countries may need to view the problem of iodine deficiency in a different light:”Rather than severe deficiency, industrialized countries have seen an increase in mild to moderate iodine deficiency, which will have an impact on neurodevelopment and may possibly impact older children as well.”
Vanderpump said a push for iodizing salt used in processed foods could help mitigate the problem of mild to moderate iodine deficiency in industrialized countries because it is safe, equitable, self-financing and cost-effective.
Problems of excess iodine
Lewis E. Braverman, MD, of Boston University School of Medicine, however, discussed issues arising from an excess of iodine. He presented data from early studies showing that healthy individuals who were given large amounts of excess iodine experienced very subtle decreases in T4 and T3 concentrations with a slight compensatory rise in thyroid-stimulating hormone, as well as study results describing the Wolff-Chaikoff effect.
Patients with other conditions, such as thyroiditis or thyrotoxiscosis, may develop hypothyroidism as a result of excess iodine, according to Braverman. An older study conducted in Iran indicated that fetuses whose mothers were exposed to excess iodine were hypothyroid at 21 days, which is equivalent to the third trimester in humans. Moreover, he said, other studies support the relationship between excess iodine intake during pregnancy and the development of hypothyroidism in the fetus.
On the other side, iodine-induced thyrotoxicosis can also occur with iodine supplementation, Braverman said. – by Melissa Foster
For more information:
Burrow G. Clinical simultaneous symposia: Iodine. Presented at: the American Thyroid Association 82nd Annual Meeting; Sept. 19-23, 2012; Quebec City.
Disclosure: Braverman, Caldwell and Vanderpump report no relevant financial disclosures.