Q. You wrote recently about selenium and said three or four Brazil nuts daily supplied enough selenium to cause toxicity. I'm taking 100 micrograms of selenium daily to ward off prostate cancer. Is this dosage of selenium safe?
A. Selenium is a fascinating mineral. Preliminary studies suggest that when people get adequate amounts in their diet, they have better immune function and reduce the risk of developing osteoarthritis. Several studies hint that selenium may help ward off prostate cancer (Harvard Men’s Health Watch, March, 2007).
Too much selenium, however, can be toxic. Symptoms may include rash, hair and nail brittleness, garlic breath, upset stomach and nerve damage). The tolerable upper limit for adults has been set at 400 micrograms per day, so your dose is safe.
An ounce of Brazil nuts (about half a dozen or so) contains roughly 800 micrograms of selenium. That’s why we suggest not eating more than a couple of Brazil nuts three or four times a week.