About 13 million Americans have been diagnosed with a thyroid disease and a research study published in February 2000, estimated that another 13 million may have a thyroid condition of which they are unaware. Approximately one in eight women will develop a thyroid disorder in her life and women are five to eight times more likely than men to have hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid).

People with thyroid conditions may suffer debilitating side effects such as depression, weight gain or loss, fatigue, nervousness, muscle weakness or cramps, hair loss, poor memory, and difficulty concentrating. These statistics show that many people may be at risk of developing thyroid disease. How can you tell if you are at increased risk? Are there ways you can prevent thyroid disorders?

The most common risk factors for thyroid disease are:

Some of these risk factors may be involved in the development of thyroid disease, though scientists are still uncertain of the exact causes.

Your Diet

There are a number of dietary factors that may influence your thyroid health. This may include:

Too little iodide

If you don’t have enough iodide your body can’t make enough of the thyroid hormones that regulate your body's energy use. This lack of iodide can cause a goiter, or enlarged thyroid gland. A chronic deficiency of this mineral can result in destruction of the thyroid gland. Because we have iodized salt in the United States, iodide deficiency and goiter are rarely seen. The recommended dietary allowance is 120 micrograms per day (mcg/d) for adults and 220 mcg/d for pregnant women.

Too much iodide

The thyroid can also become enlarged if you have too much iodide in your diet, though this is rare in the United States. This “toxic goiter�?is caused by elevated concentrations of thyroid stimulating hormone (TSH), and is often seen in people who eat a lot of seaweed, which can add a significant amount of iodide to the diet. Iodide levels up to one milligram (more than six times the Recommended Dietary Allowance) appear to be safe.

Foods that can cause problems

Some foods have chemicals that can cause goiters and inhibit thyroid gland functions if eaten in raw and in large quantities. These chemicals, called goitrogens, are destroyed when these foods are cooked. Examples of “goitrogenic�?foods include: Brussels sprouts, broccoli, turnips, rutabagas, kohlrabi, radishes, cauliflower, African cassava, millet, and kale.

There is also some evidence that soy has potential negative effects on the thyroid gland, though the evidence is conflicting. For instance, some studies have found that soy reduces the absorption of thyroid medications and may even directly inhibit the function of the thyroid gland. While others have found that soy has either no effect on thyroid hormone levels, or actually increases levels. Because of soy’s complex effects regarding the thyroid, it is recommended that people with impaired thyroid function not consume large amounts of soy products.

Radioactive Iodine

Radioactive iodine is often used to treat thyroid cancer or hyperthyroidism (overactive thyroid)—but there are also some risks. For instance, high doses of radioactive iodine (used to treat hyperthyroidism) can often cause hypothyroidism (underactive thyroid) because the iodine will concentrate in the thyroid gland during treatment.

Considerable attention has been paid to design radioactive iodine treatment that will bring the thyroid function back to normal, however, at this time the majority of people who undergo this procedure will develop hypothyroidism and be required to take synthetic thyroid hormone.

Medications

It is thought that medications such as lithium and the heart drug Cordarone may cause hypothyroidism. Lithium acts on the central nervous system and is used to treat the manic stage of bipolar disorder (manic-depressive illness). Lithium is not recommended for use during pregnancy, especially during the first three months since studies have shown that it (rarely) may cause thyroid problems and heart or blood vessel defects in the baby. Elderly people taking lithium can also develop goiter or symptoms of underactive thyroid because of their increased sensitivity to the effects of lithium. The elderly are also more likely to have thyroid problems with Cordarone (a drug used to correct irregular heartbeats). This drug increases the risk of overactive or underactive thyroid.

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Duncan AM, Merz BE, Xu X, et al. Soy isoflavones exert modest hormonal effects in premenopausal women. Journal of Clinical Endocrinology and Metabolism. 1999;84:192�?97.

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Last reviewed November 2004 by Kimberly Rask, MD, PhD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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