by Mary J. Shomon
Researchers writing in the July 15, 2000 issue of the British-based international medical journal, The Lancet, called attention to the importance of selenium to health, citing the trace mineral's potential to reduce the risk of thyroid problems, pregnancy and fertility problems, heart disease, and progression of HIV to AIDS, among other important findings.
According to the review study, diet and geographic location can impact the amount of selenium you are getting. Selenium is an essential trace mineral found in the soil. Typically, crops will convert selenium into organic forms that can be absorbed nutritionally by humans. Getting sufficient quantities of selenium may increase thyroid hormone metabolism, improve fertility, help fight cancer, and reduce risk of cardiovascular disease and arthritis.
The author of the study, ("The importance of selenium to human health," The Lancet, Volume 356, Number 9225, 15 July 2000), Margaret Rayman, a professor of nutritional medicine at the University of Surrey in Guildford, England, began focusing on selenium several years ago, after her research into the condition known as preeclampsia showed that low selenium levels were a common denominator in all the women in the study. Her research went on to discover that in the UK, and in Europe as well, selenium levels were abnormally low overall. Rayman found that dietary consumption of selenium had dropped 50% in the past two decades, a time period during which the UK had reduced it imports of selenium rich North American wheat in favor of selenium poor European wheat.
In addition to the relationship to early miscarriage, male infertility, mood problems, thyroid disorders, cardiovascular disease and arthritis, Rayman also discovered that selenium plays a key role in viral infections. In particular, higher selenium levels can help slow down the replication of the HIV virus. Her study actually found that "AIDS patients with low levels of selenium were 20 times more likely to die from an AIDS-related illness than those with healthy levels of the mineral."
In addition to selenium supplements, selenium-rich foods such as kidney, liver, crab, other shellfish, and Brazil nuts can be eaten. North American soil is also selenium rich, and crops grown in this soil have higher levels of selenium. Researchers believe that most North Americans are probably getting enough selenium, and caution that too much selenium can be toxic. The maximum level of selenium recommended per day for adults is 400 micrograms per day. However, some studies have shown that certain areas of the U.S., including, for example, the Eastern Coastal plain of the U.S., have selenium-deficient soil as well, so dietary exposure to selenium may be inconsistent.
Regarding the thyroid, selenium is a component of the enzyme that helps convert T4 to T3 peripherally, so deficiencies of selenium may impair thyroid function and promote hypothyroidism. According to the New England Journal, "selenium deficiency can result in thyroid injury and decreased extrathyroidal triiodothyronine production" (reduced peripheral T3 production.) Some experts believe that low T3 levels may be characteristic in areas with insufficient selenium. Studies also show that excess intake of selenium may also depress T3 levels. With some scientists suspecting that there may be a viral component or trigger to certain autoimmune conditions such as the common thyroid condition known as Hashimoto's Disease, the anti-viral properties of selenium also become more interesting, and further research into that connection as relates to thyroid disease particularly would be illuminating.
Implications for Patients: The key issue for thyroid patients is making sure you get enough, but not too much, selenium. Talking to a good nutritionist or holistic physician can help you determine if selenium might help your health and thyroid function.
FOR MORE INFORMATION ON SELENIUM, HEALTH AND THYROID FUNCTION:
- Selenium -- Rick Hall's About Nutrition Site provides a summary review of dietary selenium
- UC Berkley's Wellness Guide to Dietary Supplements -- Selenium -- An in-depth review of selenium
- Selenium Forum -- provides information to nutrition researchers, health care providers, media and consumers on the functions, actions and clinical effects of dietary selenium.
- Ithyroid's Review of Selenium -- Thyroid-focused nutritional information on selenium
- Selenium May Help Prevent Certain Types of Cancer, JAMA: 12/24/96
- New Discoveries Expand Our Knowledge About Selenium's Importance--An excellent HealthyNet article
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