Many brands of multivitamins for pregnant women may not contain all the iodine they claim, potentially putting babies at risk of poor brain development, a new study suggests.
Tests on 60 brands that listed iodine as an ingredient on their labels found many fell short of the stated amount. The risk of too little iodine appears greater with "natural" vitamins that get their iodine from kelp rather than a salt form, the study found.
"If these numbers are all real, then they're not meeting their label claim and that's a problem," said William Obermeyer, a former Food and Drug Administration scientist who co-founded ConsumerLab.com, a private testing service. Obermeyer was not part of the research.
The study was done by scientists at the Boston University Iodine Research Laboratory. Results were reported in a letter published in Thursday's New England Journal of Medicine. No brands were named in the analysis.
Iodine is commonly added to table salt and can be found in seafood, dairy products and bread. Iodine deficiency affects more than 2 billion people worldwide and is the leading cause of mental retardation.
Pregnant and nursing women need 220 to 290 micrograms of iodine a day, according to the Institute of Medicine. Expecting mothers who don't get enough can put their babies at greater risk of mental retardation and growth, hearing and speech problems.
The American Thyroid Association recommends that pregnant women take a daily dose of prenatal multivitamins containing 150 micrograms of iodine, which is needed for proper thyroid function. During pregnancy, having enough thyroid hormones is important for fetal brain development.
There is no law requiring vitamin makers to add iodine to prenatal multivitamins, which are available by prescription or bought over-the-counter as dietary supplements.
Boston University scientists last year looked at 223 prenatal multivitamins available by prescription or sold over-the-counter in the United States. About half of them -- 114 -- listed iodine on their labels.
Prescription prenatal vitamins face more stringent government scrutiny than their supplement counterparts, which do not have to be proven safe before they are sold.
However, researchers found problems with both types when they tested iodine levels in 60 prescription and over-the-counter prenatal multivitamins. The iodine was in the form of kelp or potassium iodide.
Among vitamins with potassium iodide, tests found the average iodine level was 119 micrograms per daily dose -- less than the recommended amount.
Among kelp-containing vitamins, the iodine levels ranged from 33 to 610 micrograms per daily dose. Experts say taking too much iodine can lead to problems, especially for women who already have a thyroid problem.
In 10 brands, iodine levels were less than half than what was listed on their labels. Three brands contained iodine levels 50 percent or more higher than advertised. Variations were greater among kelp-containing vitamins.
Based on the study's findings, pregnant women should take prenatal multivitamins that contain potassium iodide instead of kelp, said Dr. Elizabeth Pearce, one of the researchers.
Dr. Alex Stagnaro-Green, who specializes in pregnancy thyroid problems at the Touro University College of Medicine in New Jersey, said the findings point out a problem in vitamin marketing and urged the Food and Drug Administration to make iodine a mandatory ingredient in all prenatal multivitamins.
The Council for Responsible Nutrition, a Washington-based trade group for vitamin makers, said it supports putting iodine in all prenatal vitamins. The council's John Hathcock said iodine is difficult to measure and can degrade over time, which can affect its concentration.
Some independent groups such as the United States Pharmacopeia test dietary supplements to verify their contents. Consumers can buy brands with a seal of approval from USP.