Antioxidants are gimmicky -- they have been included in everything from diet pills to beauty products, whether or not scientific evidence exists to back up the claims. Selenium is an antioxidant that has been inexplicably marketed as a weight loss aid -- even though most evidence points away from this conclusion. It has shown promise in the treatment of a particular thyroid condition that can cause obesity, but most cases of obesity are caused by excess calories and not enough exercise, not a thyroid condition.
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Selenium
Selenium is an antioxidant mineral found in wheat germ, butter, fish, garlic, nuts and seeds. It is primarily an antioxidant, gathering free radicals as it circulates through the body, thereby protecting your DNA and cells. It's necessary for proper immune system function and may have an effect on certain immune-mediated diseases. The property that has the supplement world abuzz, however, is its effect on the thyroid. There is a tendency in weight loss culture to blame chronic obesity on improper thyroid function, whether lab tests show it or not. Whether or not this is the case has yet to be proven, but even if it is true, selenium is probably not the answer.
Effects on the Thyroid
If your obesity is caused by a thyroid condition, it is an underactive rather than overactive thyroid that is to blame. MedlinePlus, an online resource of the National Institutes of Health, rates selenium as "possibly effective" for treating Hashimoto's thyroiditis, a condition in which your immune system attacks your thyroid, causing inflammation that can lead to an underactive thyroid and obesity. It is thought, however, that the selenium calms the immune system rather than activating the thyroid, so synthetic thyroid hormone is still needed to regain normal thyroid function. If you have been diagnosed with Hashimoto's thyroiditis, ask your doctor about adding selenium to your treatment plan. Selenium may actually worsen other forms of underactive thyroid, especially when an iodine deficiency is present.
Body Composition
A 2003 study in "The Journal of Nutrition" investigated selenium's effect on thyroid function and body composition in a group of men. On the 64th day of the study, the group of men receiving high selenium doses began to gain weight, and by the 92nd day, the weight gain was significant. Both the groups receiving high and low doses of selenium increased their muscle mass, but the group receiving low doses reduced their fat mass. The researchers concluded that the selenium did alter the thyroid function in both groups, but that high doses may actually trigger a hypothyroid-type response, decreasing energy expenditure and increasing weight.
Safety
The minimum daily recommended intake of selenium is 55 mcg, and the upper tolerance is 400 mcg. According to MedlinePlus, most Americans get about 125 mcg per day just from their food -- so unless you are using selenium to treat a specific medical condition, you are already probably getting enough. Selenium supplements may interact with cholesterol drugs, anticoagulants, sedatives and oral contraceptives, so consult your doctor before use if you are taking any medication. Selenium is considered safe for short-term use, but long- -term use may increase your risk of diabetes, cancer and death from any cause.