Iodine fortification during pregnancy

TOPIC: Prenatal multivitamin pills

Title: Iodine Content of U.S. Prenatal Multivitamins

Authors: Leung AM, Braverman LE, Pino S, He X, & Pearce EN.

Reference: Thyroid 18 (Suppl. 1) S-45, 2008 Abstract of a poster presented at the 79th Annual Meeting of the American Thyroid Association (Chicago, October 2008)

Summary

Background

Adequate maternal iodine intake during pregnancy and lactation is essential for thyroid hormone production in the fetus and neonate. The Institute of Medicine recommends a daily iodine intake of 220 µg in pregnancy and 290 µg in lactation. The American Thyroid Association (ATA) recommends vitamin supplements containing 150 µg of iodine daily during pregnancy and lactation, yet the iodine content of U.S. prenatal multivitamins is not mandated.

Methods

Using the Internet, the authors found 127 non-prescription and 96 prescription prenatal multivitamins marketed in the United States.

Results

Sixty-nine percent (N=87) of non-prescription and 28% (N=27) of prescription brands listed iodine as a constituent. Of 114 iodine-containing prenatal multivitamins, 101 (89%) listed ≥150 µg/serving [kelp, n=42; KI, n=67; other, n=5]. Since 150 µg KI contains only 76% (114 µg) iodine, current labelling is misleading. The iodine content of 60 iodine-containing brands was measured. Measured iodine content per serving in 35 KI-containing vitamins was 119 (mean) ± 14 (SE) µg, which was similar to 120 ± 7 µg of iodine, calculated as 76% of the labelled KI. The measured iodine-containing brands prepared from kelp contained 33-610 µg/serving. Fourteen of 25 had iodine levels that were ≥50% discordant with listed values (including 10 that were lower by ≥50%), likely due to variation in kelp iodine content.

Conclusions

Only 69% of non-prescription and 28% of prescription U.S. prenatal multivitamins contain iodine. Multivitamins containing iodine as kelp have variable iodine content. Although more consistent, multivitamins from KI also are misleading, since the iodine content is only 76% of the labelled KI. Prenatal multivitamin manufacturers should be encouraged to use only KI, to maintain consistency in labelling, and to include ≥197 µg KI/serving to ensure 150 µg of supplemental daily iodine, as recommended by the ATA.

Commentary

Iodine deficiency during pregnancy and childhood has serious consequences. Severe iodine deficiency during pregnancy results in miscarriage and cretinism, while inadequate iodine intake during a child’s development can lead to goiter and learning disabilities. Adequate iodine supplementation can eradicate these deleterious outcomes. Theoretically, iodine deficiency can be eliminated through a combination of universal salt iodination and mandatory inclusion of iodine in prenatal vitamins. Yet, despite international efforts, spanning several decades, the World Health Organization estimates that worldwide iodine deficiency still occurs today in 2 billion people ( NEJM , 354:2819, 2006). Adequate iodine intake is particularly critical during pregnancy as the iodine needs are increased due to a 50% rise in thyroid hormone production and increased renal iodine losses.

Iodine status in the United States has been periodically assessed since the early 1970s through the National Health and Nutrition Examination Surveys (NHANES). A decrease in median urinary iodine concentration (UIC) was observed between NHANES I (1970s) and NHANES III (1988-1994). Specifically, the median UIC decreased from 320 µg/L to 145 µg/L. Of particular concern in NHANES III, was that 14.9% of women between the ages of 15-44 years, and 6.9% of pregnant women, had median UIC of ≤50 µg/L (Public Health Nutrition, 10:1532, 2007). Iodine deficiency is defined as a median UIC of less than 100 µg/L ijn a given population. These data raise the question as to whether or not a segment of pregnant women in the United States may suffer from iodine deficiency.

The abstract presented by Leung and colleagues at the annual meeting of the American Thyroid Association in 2008 provides an analysis of the iodine content in prenatal vitamins (PNVs) in the United States. The compelling data from their abstract are as follows:

  1. there is a minimum of 221 PNVs available in the US (96 of them available by prescription only);
  2. only 69% of non-prescription PNVs and 28% of prescription PNVs contain iodine;
  3. kelp was the source of iodine in 42 of the 101 iodine-containing PNVs; and
  4. the iodine content measured in kelp-containing PNVs was markedly discordant with the labelling, while the iodine content of KI containing PNVs was more accurately reflected in the label.

In summary, the multitude of PNVs in the United States, the lack of iodine in the majority of prescription brand PNVs and a third of non-prescription PNVs, and the variable content of iodine measured in kelp containing PNVs, leads one to conclude that whether or not a pregnant woman receives an iodine containing PNV (or if she does what the iodine content is) is simply a chance occurrence. The study of Leung and colleagues, in conjunction with the recent NHANES III data, should serve as a call to action to prevent iodine deficiency during pregnancy in the US. It is time for medical organizations to work together to mandate that all PNVs contain a minimum of 150 µg of KI. Editorial written by Alex Stagnaro-Green (Related to Chapters 14 & 20 of TDM)