Iodine Status and Thyroid Function of Vegetarians and Vegans

There is clinical evidence that iodine is important for the proper functioning of the thyroid gland. Some chemicals, like thiocyanate and perchlorate found in the environment, affect the functioning of the thyroid. This study attempted to evaluate the levels of iodine among vegetarians and vegans and whether thyroid functions were affected by the intake of thiocyanate and perchlorate present in certain vegetables. It was found that while vegetarians have adequate levels of iodine in their body, vegans might be at a risk of iodine deficiency. The study also found that thiocyanate and perchlorate do not create a risk of iodine deficiency for vegetarians and vegans.

Since the 1920s, the population of the United States is said to have minimal cases of iodine deficiency. About 2.2 billion cases of iodine deficiency are reported at present. Pregnant and breastfeeding mothers are at the greatest risk of suffering from iodine deficiency, as they need more than the regular amount of iodine to compensate for the baby’s growth. Iodine is available in dairy products, iodized salt, seafood, eggs and bread. Vegetarians (who consume animal products like eggs and milk along with vegetables) and vegans (who do not consume foods of animal origin) constitute 2.5 percent of the American population, and they may be vulnerable to iodine deficiency because of their dietary patterns. This study, therefore, seeks to find out whether iodine deficiency exists in this population.

* This study was carried out in 2010 on 78 vegetarians and 63 vegans. All the participants were from the Boston area and were aged above 18 years. All the participants had been following a vegan or vegetarian diet for three consecutive months. Those who were suffering from any kind of thyroid disease, used a thyroid hormone, used medications containing iodine, or were pregnant, were not included in the study.
* The ethnicity, age, gender, birthplace, family history, medical history, diet, intake of vitamins or supplements containing iodine, smoking habits and other details were recorded.
* The levels of iodine, thiocyanate and perchlorate were tested from urine samples using spot urine tests.

Results/key findings
* On an average, the vegans had a lower urine iodine level by half compared to vegetarians.
* The levels of iodine in vegans were comparatively low from the general non-vegetarian U.S. population. Vegans are found to have more cases of iodine deficiency because they do not consume dairy products, which are a main source of dietary iodine. It was, however, found that the deficiency in iodine was not high enough to cause a thyroid dysfunction.
* The difference in iodine levels of the vegetarians from the non-vegetarians was not significant.
* Exposure to environmental perchlorate and thiocyanate that naturally occur in vegetables was not found to affect the functioning of thyroid gland.

Next steps/Shortcomings
The authors of this study agree that it included a very small number of participants and further studies on larger populations are necessary to arrive at definite conclusions. They also admit that participants who were found to have low levels of iodine in their urine may not have ingested iodine-rich food prior to the study, but they may otherwise consume iodine-rich foods on a regular basis. Since a single spot urine test was used for assessing iodine levels, it cannot be accurately correlated with thyroid functioning. More spot urine tests would be required to correlate them with thyroid function.  Most of the participants in the vegetarian group were Asians and more diversified studies should be done in the future.

Although the population of the United States is not considered to be iodine deficient, the data obtained in this study is important. This is the first study to evaluate iodine levels in vegetarians and vegans. Vegans are found to be at a greater risk of iodine deficiency than vegetarians and the general population. This data is specifically important for vegan and vegetarian women of childbearing age. The American Thyroid Association recommends that pregnant and breastfeeding women consume 150 µg of iodine per day in order to avoid mental retardation and other problems in their babies. This study also confirms that perchlorate and thiocyanate that are naturally found in foods do not have any significant effect on iodine levels and thyroid functioning. However, authors suggest performing further studies to evaluate the role of environmental thiocyanates and perchlorates in the inhibition of iodine levels and thyroid functioning in humans.

For More Information:

Iodine Status and Thyroid Function of Boston-Area Vegetarians and Vegans
Publication Journal: Journal of Clinical Endocrinology and Metabolism, May 2011
By Angela M. Leung; Andrew LaMar
From the Boston University School of Medicine, Boston, Massachusetts

*FYI Living Lab Reports Are Summaries of the Original Research.

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