Selenium is safe at the level people typically supplement (100–200 mcg); however, taking more than 900 mcg of selenium per day has been reported to cause adverse effects in some people.265 Selenium toxicity can result in loss of fingernails, skin rash, and changes in the nervous system. In the presence of iodine-deficiency-induced goiter, selenium supplementation has been reported to exacerbate low thyroid function.266 Although most research suggests that selenium prevents cancer, one study found an increased risk of a type of skin cancer (squamous cell carcinoma) in people taking selenium supplements.267 The National Academy of Sciences recommends that selenium intake not exceed 400 mcg per day, unless the higher intake is monitored by a healthcare professional.268 In a double-blind study of people who took 200 mcg of selenium per day for several years to prevent recurrences of skin cancer, the incidence of diabetes was higher in people who received selenium (9.7%) than in those who received a placebo (6.5%).269 While this difference was statistically significant, this finding should be considered preliminary, since the study was not originally designed to test whether selenium influences the risk of developing diabetes.
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The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2015.