Selenium, a trace mineral required by your body in minute amounts, can have harmful effects if taken in excess. Selenium was considered a poison when discovered in 1817, according to the University of California at Berkeley's Wellness Letter. Your daily intake of selenium is easily obtainable from dietary sources in the United States. Brazil nuts contain large amounts of selenium.
Dosage
The maximum acceptable daily intake for selenium is 400 micrograms per day for people over 14. Children between 9 and 13 should consume no more than 280 micrograms, those from 4 to 8 should get no more than 150 micrograms, and children from 1 to 3 should take in no more than 90 micrograms. Your dietary requirement for selenium is 55 micrograms per day. Three to four Brazil nuts, or a 1/2 oz. serving, contain 272 micrograms. The Wellness Letter recommends eating no more than two Brazil nuts per day to avoid overdosing on selenium.
Deficiencies
Eating just one Brazil nut per day could prevent selenium deficiency, since a single nut contains up to 100 micrograms of selenium, depending on the soil where it's grown, the Linus Pauling Institute states. Countries with low selenium content in the soil include Russia and China, where selenium deficiencies occur more often. People receiving all of their nutrition from total parenteral nutrition, or TPN, also might develop selenium deficiency. Studies show that in U.S. areas with low soil selenium levels, certain cancers, such as nonmelanoma skin cancer, occur more frequently, the Office of Dietary Supplements reports. Diseases associated with selenium deficiency include a heart disease called Keshan disease, hypothyroidism that can lead to mental retardation, and immune deficiencies.
Benefits
Benefits of increased selenium by ingesting just one Brazil nut per day can include a reduced risk of a number of cancers. A look at three separate studies shows that increased serum selenium correlated with a 34 percent lower risk of developing polyps associated with colon cancer, the Wellness Letter reports. The SELECT study, which examined the benefits of selenium and vitamin E in preventing prostate cancer, was discontinued when no benefit was found after 5.5 years. Studies on the effects of selenium supplementation on immune diseases such as HIV and its antioxidant effects in heart disease might help determine whether selenium can benefit different health conditions.
Toxicity
Eating Brazil nuts in large amounts can cause selenium overdose. Since the soil content determines the amount of selenium in each nut, the content can range from 10 to 100 micrograms per nut. Symptoms of selenium overdose include skin rash, brittle hair and nails, white blotchy spots on nails, irritability, stomach upset, fatigue and nervous system disturbances.
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