Evidence suggests that selenium at intakes greater than recommended are beneficial to the health in terms of reduction in chronic disease and improved immune status. For example, evidence reported by Clark1 showed that 200µg of selenium per day reduces the risk of some cancers by 50%. Selenium is generally well absorbed with absorbance being between 44 and 70%. The selenium content of food varies with the geographical location as concentrations in plant tissue are dependent on soil selenium. New Zealand has low selenium soils and the population therefore has marginal selenium status. Some plants accumulate selenium, with brazil nut tree being such an example. Brazil nuts are a good source of selenium because the nuts generally are harvested from wild trees which have extensive root systems that allow the plant to bioaccumulate the mineral. Reports suggest that brazil nuts contain between 8 and 83µg selenium per gram.
Researchers2 have investigated the efficacy of brazil nuts at improving selenium status compared to a 100µg supplement of selenium as selenomethionone. Subjects from New Zealand consumed 2 brazil nuts, 100µg of selenium as selenomethionine or a placebo for 12 weeks. The Brazil nuts provided a mean intake of 53µg selenium per day with a range of 20 to 84µg. Plasma levels of selenium increased by 64.2%, 61.0% and 7.6% in the brazil nut, selenomethionine and control groups, respectively. In addition, there was an increase in the glutathione peroxidise (GPx) activity in plasma in the brazil nut group (8.3%), selenomethionine group (3.4%), but a decrease in the control group (-1.2%). Whole body glutathione concentrations also increased more in those subjects consuming brazil nuts (13.2%) and the selenomethionine (5.3%) compared to the control group (1.9%). Consumption of two Brazil nuts daily therefore appears to be effective at raising selenium status.
The changes in the plasma selenium and plasma GPx activity of the brazil nut group and selenomethionine group were significantly different from the placebo, but not from each other. However, interestingly, the whole body GPx activity was significantly higher in the brazil nut group than the selenomethionine group after 12 weeks of supplementation. The mean intakes of selenium in New Zealand have been estimated to be 56µg in men and 39µg in women, supporting a viewpoint that supplementation would be necessary to achieve optimal selenium concentrations in the population. However, research has shown that Brazil nuts are also able to accumulate barium and radium because of their extensive root system. High concentrations of the 228Ra breakdown product 228Th have been detected in the urine of subjects fed 25g or more of Brazil nuts per day, suggesting that selenomethionine is a safer option.
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