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Researchers at the Boston Medical Center published their findings that a small sample of vegans have unexpectedly low levels of iodine. This finding may be important for early treatment and detection of thyroid disease.

Low Levels Do Not Seem to Cause Thyroid Problems

The human body uses iodine to make thyroid hormone. Deficiencies of iodine can cause hypothyroidism, a complex disease that can cause fatigue, slow development in children, "brain fog," dry skin, and easy weight gain. Iodine deficiencies during pregnancy may be especially detrimental to the development of the unborn child's brain. The disease once called cretinism is the result of iodine deficiency during fetal development.

T
oo much iodine, however, is also detrimental. Excesses of iodine can cause hyperthyroidism, presenting the opposite of many of the symptoms of iodine deficiency. Hyperthyroidism paradoxically can lead to hypothyroidism as the immune system attacks the overactive thyroid.

Led by Dr. Angela Leung, the Boston Medical Center researchers took urine samples from 140 vegetarians and vegans, most of them women, to measure for iodine. The more iodine the body has in bloodstream circulation, the more iodine will appear in a urine sample. Less than 100 micrograms of iodine per liter of urine indicates iodine deficiency.

Vegetarian women had iodine levels averaging 147 micrograms per liter. Vegan women had iodine levels averaging 79 micrograms per liter, indicating iodine deficiency.

Why should vegan women have iodine deficiencies? The researchers point out that only part of the iodine in the diet is provided by iodized salt. Iodine is also provided by meat, shellfish, eggs, and sea vegetables. "Vegetarian" women may sometimes indulge in eggs or even in shellfish, but vegan women shun foods of any animal source. They do not receive as much iodine in their diets.

While a vegan diet may cause lower iodine levels, the research team found no evidence that vegan women suffered any detrimental effects of their lower iodine levels. Thyroid function in both groups was equal. Neither were there any indications that vegans suffered by eating more servings of vegetables in the cabbage family, which contain sulfur compounds that can bind to iodine so that it is not available for the thyroid.

The researchers believe that had they studied more people, differences in thyroid function might have been detectable. For the time being, they advise doctors to make sure that their vegan patients do not have any problems caused by iodine deficiency. Doctors are advised to pay special attention to the nutritional needs of vegan women who are pregnant or breastfeeding.

If you think you may be at risk of iodine deficiency, what should you do?

It is important not to overdose iodine. Too much iodine taken over a short period can make your skin break out. Too much iodine taken over a long period can cause a form of hyperthyroidism called Grave's disease than inevitably leads to hypothyroidism as the thyroid "burns out."

Experts also counsel avoidance of kelp-based supplements because the iodine content in the supplements is too variable. Eating a serving of sea vegetables (for example, dulse, kombu, or kelp) once or twice a week, however, usually is enough to prevent deficiency. It is also possible to take supplemental potassium iodide, the same chemical used for radiation protection, but if you are going to take iodide supplements, be sure you also take copper, zinc, and selenium to provide all of the mineral elements needed for thyroid health.

  • Leung AM, Lamar A, He X, Braverman LE, Pearce EN. Iodine Status and Thyroid Function of Boston-Area Vegetarians and Vegans. J Clin Endocrinol Metab. 2011 May 25. [Epub ahead of print]