Most iodine supplements mislabeled, study says

BOSTON (Reuters) - Most multivitamin supplements that contain iodine carry less -- and sometimes far less -- of the element than stated on the label, possibly putting newborns at risk for developmental delays, U.S. researchers said on Wednesday.

Doctors at Boston University Medical Center tested the iodine content of 60 multivitamins with iodine and found that only 28 percent contained the full amount stated on the label.

In the remaining cases, the products designed to prevent iodine deficiency were deficient themselves, including some only available by prescription, they reported in the New England Journal of Medicine.

The American Thyroid Association's recommended daily dose for pregnant and lactating women is 150 micrograms per day. Among the 44 products that claimed to deliver that amount, one third had less than half that amount.

Iodine deficiency affects more than 38 percent of the world's population and is the leading cause of preventable mental retardation. A Chinese study of children with moderate or severe iodine deficiency found that giving them supplements typically added 13 points to their long-term IQ score.

Lack of iodine is less of a problem in developed countries, where the element is added to table salt. But iodine levels have been declining in richer countries, in part because less salt is being used out of concern for its effect on high blood pressure.

"The amount of iodine in the U.S. diet is still sufficient overall, but it has dropped dramatically, and most dramatically in women of childbearing age. It's their fetuses who are really at risk, and we have no way of identifying individuals who are iodine deficient," Dr. Elizabeth Pearce of Boston University Medical Center, who worked on the study, said in a telephone interview.

In some cases, the labeling is misleading because. For example, in products containing potassium iodide, only 76 percent of the amount stated on the label is available to the body. Another source of iodine is kelp, but that can vary widely in iodine content.

Pearce said pregnant women should look for a prenatal multivitamin or supplement with potassium iodide as the source because it is less variable.

"They should use iodized salt if they're adding salt, but probably the best source in addition to the multivitamin is dairy foods," she said.

(Editing by Julie Steenhuysen and David Wiessler)