Absorption and Bio-availability

Reference from the joint report of FAO/WHO expert consultation on Human Vitamins and Minerals verbatim.

80. WHO. 1987. Selenium, Geneva, World Health Organization. (Environmental Health Criteria, 58).

81. Patterson, B.H., Zech, L.A., Swanson, C.A. & Levander, O.A. 1993. Kinetic modelling of selenium in Humans using stable isotope tracers. J. Trace Elem. Electrolyte Health Dis. 7: 117-120.

Selenium compounds are generally very efficiently absorbed by humans, and selenium absorption does not appear to be under homeostatic control (80). For example, absorption of the selenite form of selenium is greater than 80 percent whereas that of selenium as selenomethionine or as selenate may be greater than 90 percent (80, 81).

40. Contempre, B., Le Moine, O., Dumont, J.E., Denef, J-F. & Many, M.C. 1996. Selenium deficiency and thyroid fibrosis. A key role for macrophages and TGF-á. Mol. Cell. Enyzmol., 124: 7-15.

Therefore, the rate limiting step determining the overall availability of dietary selenium is not likely to be its absorption but rather its conversion within tissues to its metabolically active forms (e.g., its incorporation into GSHPx or 5'-deiodinase) (40).

 82. Mutanen, M. Bio-availability of selenium. Ann. Clin. Res.,1986; 18: 48-54.

A number of depletion-repletion experiments have been carried out on animals to estimate the bio-availability of selenium in human foods (82). 

Based on the restoration of GSHPx activity in depleted rats, the bio-availability of selenium in wheat is quite good, usually 80 percent or better. The selenium in Brazil nuts and beef kidney also appears readily available (90 percent or more by most criteria). The selenium in tuna seems of lesser availability (perhaps only 20–60 percent of that from selenite) whereas the availability of selenium from certain other seafoods (shrimp, crab, and Baltic herring) is high.

83. Levander, O.A. 1983. Bio-availability of selenium to Finnish men as assessed by platelet glutathione peroxidase activity and other blood parameters. Am. J. Clin. Nutr., 37:887-897. 

The selenium in a variety of mushrooms appears to be of uniformly low availability to rats. Data on the nutritional bio-availability of selenium to humans are sparse. A supplementation study carried out on Finnish men of relatively low selenium status showed that selenate selenium was as effective as the selenium in seleniferous wheat in increasing platelet GSHPx activity (83).

The wheat selenium, however, increased plasma selenium levels more than did selenate selenium and once the supplements were withdrawn, platelet GSHPx activity declined less in the group given wheat. This study showed the importance of estimating not only short-term availability but also long-term retention and the convertibility of tissue selenium stores into biologically active forms.