Brazil nuts may be as effective as selenium supplements in raising selenium levels, suggests a new study from New Zealand.

Selenium is essential to build selenoproteins, which take part in antioxidant defense, thyroid metabolism, immune function, and reproduction. Low selenium levels result in reduced amounts of selenoproteins, which has been linked to greater risk for cardiovascular disease, cancer, altered immune function, infertility and other conditions. In light of this, Christine Thomson and colleagues from the University of Otago, New Zealand, decided to study the effectiveness of Brazil nuts in improving selenium status, because Brazil nuts are the richest known dietary source of selenium.

The researchers recruited 60 people screened for low blood selenium (30 men and 30 women) and randomly assigned them to 3 groups of 20 subjects: group one received daily 2 Brazil nuts providing 53 µg Se on average, group two received a supplement containing 100 μg of selenium in the form of the amino acid selenomethionine, and group three received a placebo. Total duration of the study was 12 weeks and blood samples of the participants were taken at the beginning and at weeks 2, 4, 8 and 12, to measure selenium in blood plasma and the activity of glutathione peroxidase, a selenoprotein enzyme, in plasma and whole blood. As long as the activity of glutathione peroxidase keeps increasing with selenium supplementation, people are considered not to have reached optimal selenium status.

Analyses of the blood samples showed that plasma selenium concentration significantly increased by about 60% in both the Brazil nuts and the supplement group compared to an 8% increase in the placebo group. Activity of glutathione peroxidase in plasma was improved in both treatment groups, but with a tendency to increase more in the group consuming Brazil nuts. In contrast, whole blood glutathione peroxidase activity increased significantly only in the group receiving Brazil nuts.

The authors concluded that Brazil nuts are as effective as selenium supplements in improving selenium status. However, these nuts increased the activity of glutathione peroxidase in whole blood more than supplements, which suggests that selenium from Brazil nuts is more bioavailable and may be more effective in the long term.

These findings add to research showing heart-health benefits of various kinds of nuts. A very recent study attributed cholesterol-lowering properties to Macadamia nuts, and current evidence supports the idea of consuming a handful of nuts a day in order to help reduce heart disease risk.

For more information, see:
Thomson CD et al (2008). Brazil nuts: an effective way to improve selenium status. American Journal of Clinical Nutrition. 87(2):379–384.

EUFIC-related material:
Food Today n°59 (2007) All about nuts.
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