Healthnotes Newswire (April 3, 2008)—Some people worry about eating nuts because they are high in calories and fat, but numerous studies have found that eating nuts actually helps us stay healthy. A new study showing that Brazil nuts are a good source of selenium might help explain why eating this type of nut is beneficial.

Selenium is a trace mineral used in the body to make enzymes that promote (catalyze) chemical reactions. Selenium deficiency diminishes immune function and appears to be associated with increased risk of viral infections, some cancers, and heart disease.

The study, published in the American Journal of Clinical Nutrition, included 59 people with low blood levels of selenium. They were randomly assigned to eat two Brazil nuts or take a supplement providing 100 mcg of selenium or a placebo every day for 12 weeks. An analysis of a sample of nuts used in the study found that two Brazil nuts provided an average of 53 mcg of selenium, with a range of 20 to 84 mcg.

At the end of the study, both the Brazil nut and supplement groups had higher selenium, and higher activity in a powerful selenium-dependant antioxidant enzyme (glutathione peroxidase) than they had at the beginning. Even though the Brazil nuts probably had less selenium than the supplement, the increases in selenium were similar and the increases in the enzyme were higher in the group that ate the nuts. Selenium levels and glutathione peroxidase activity did not change in the placebo group.

Brazil nuts are the richest food source of selenium, although the amount can vary greatly depending on the soil where the tree grows. This is the first study to show that eating Brazil nuts can effectively improve selenium status. The difference in glutathione peroxidase activity between people taking the supplement and people eating Brazil nuts suggests that the selenium in the nuts is more readily absorbed and used by the body (more bioavailable).

The Daily Reference Intake for selenium in the United States is 55 mcg for adults, but many scientists think that 100 to 200 mcg per day is a better amount. Although selenium deficiency is rare in the developed world, people living in places with selenium-poor soil (such as New Zealand and parts of China) are still vulnerable.

“There is growing interest in taking higher amounts of selenium than are currently recommended, and evidence suggests that these higher intakes might protect against cancer and other chronic conditions,” said lead study author Professor Christine Thomson, PhD, of the Department of Human Nutrition, University of Otago in New Zealand.

In addition to Brazil nuts, food sources of selenium include oysters and clams, organ meats like liver and kidney, wheat flour and wheat germ, molasses, and sunflower seeds.

Though consumption should be limited to no more than a few nuts per day to avoid toxic accumulation of selenium in the body’s tissues, Thomson said, “In light of the results from our study, showing that Brazil nuts are a good source of bioavailable selenium, adding a few to the daily diet is a reasonable way to increase selenium intake and improve selenium status.”

(Am J Clin Nutr 2008;87:379–84)