RESUMO
The Japanese recommended dietary allowances (RDA) for major and some minor nutrients were revised in 1999, and included those for trace elements such as selenium. The requirement of selenium in animals was first recognized in 1957. It has been shown that cellular glutathione peroxidase (GPx) contains selenium but it was subsequently revealed that selenium has diverse biochemical effects, rather than simply functioning in the enzyme. At least twelve different selenoproteins have been identified. The role of selenium has been known as antioxidant, and non-antioxidant mediated through these enzymes. Now, selenium is well recognized as a preventive factor for cancer and cardiovascular diseases. Several dietary studies have shown that the selenium intake in Japan is adequate. One study estimated daily selenium intake to be 104.2 micrograms/day for adults. This value was 2 or 3 times higher than the lower limit of the safe range of dietary selenium (40 micrograms/day for men and 30 micrograms/day for women) estimated by WHO, and also exceeded the newly established RDA of 55-60 micrograms/day for men and 45 micrograms/day for women by the Japanese Public Health Council. However, the established RDA for selenium is tentative because of a lack of information on the 1) chemical forms of selenium in food, 2) differences in absorption rate and bio-availability in the chemical forms, and 3) interactions with other metals and trace elements. There are two potential problems concerning selenium nutrition in Japan. The first problem is that rice, which is the Japanese staple food, contains less than 0.05 microgram/g selenium whereas U.S. rice contains more than 0.3 microgram/g, probably due to differences in soil chemistry. The second problem is that although studies have shown that seafood, fish, shellfish and oysters, contain high levels of selenium (0.4-0.5 microgram/g), these being the main selenium source for Japanese, the bio-availability in fish is low. Thus, it is likely that the selenium status of those Japanese who eat an imbalanced diet is not sufficient or is not optimal even if the intake exceeds the RDA. Further studies are needed so that community health care specialists have available appropriate knowledge on the role of trace nutrients, including selenium, in human nutrition and health, to promote proper nutritional practices in the community.