Criteria for Assessing Selenium Requirements

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

84. Levander, O.A. 1988. The global selenium agenda. In: Trace Elements in man and animals - 6. Proceeding of the 6th International Symposium on Trace Elements in Man

and Animals. Hurley, L.S., Keen, C.L., Lonnerdal, B., Rucker, R.B. eds. New York Plenum Press Inc.

Levander (84) convincingly illustrated the impracticability of assessing selenium requirements from input-output balance data because the history of selenium nutrition influences the proportion of dietary selenium absorbed, retained, or excreted. The changing equilibria when selenium intake is varied experimentally yield data which are of limited value for estimating minimal requirements. 

Examples are cited of estimates of selenium requirement for adults of 7.4 and 80 μg/day derived from Chinese and United States studies, respectively. Such discrepancies reflect differences in the usual daily selenium intakes of the experimental subjects and the extent to which this was changed experimentally. This situation, not unique to selenium, emphasises the importance of basing requirement estimates on functional criteria derived from evidence describing the minimum levels of intake which, directly or indirectly, reflect the normality of selenium-dependent processes.

85. Gu, Q-P., Xia, Y-M., Ha, P-C., Butler, J.A. & Whanger, P.D. 1998.Distribution of selenium between plasma fractions in guinea pigs and Humans with various intakes of selenium. J. Trace Elem. Med. Biol., 12: 8-15. 

New opportunities for the development of biochemical indexes of selenium adequacy such as those listed in Table 47 have yet to be exploited. Until this is done, the most suitable alternative is to monitor changes in the relationship of serum selenium to dietary selenium supply, taking advantage of its relatively constant proportionality to the fraction of serum selenium in functionally significant GSHPx (85).

for each of these references above here...

76. Alfthan, G. & Neve, J. 1996. Reference values for serum selenium in various areas evaluated according to the TRACY protocol. J. Trace Elem. Med. Biol., 10: 77-87.

A detailed review of 36 reports describing serum selenium values in healthy subjects indicated that they ranged from a low of 0.52 μmol/l in Serbia to a high of 2.5 μmol/l in Wyoming and South Dakota in the United States (76). 

It was suggested that mean values within this range derived from 7502 apparently healthy individuals should be regarded tentatively as a standard for normal reference. This survey clearly illustrated the influence of crop management on serum selenium level; in Finland and New Zealand, selenium fortification of fertilisers for cereals increased serum selenium from 0.6 to 1.5 μmol/l. A summary of these data in Table 51 also includes representative mean serum selenium values within the range of 0.15–0.55 μmol/l reported for specific diseases known to be associated with disturbances in selenium nutrition or metabolism.

86. WHO/FAO/IAEA. 1996. Trace elements in Human nutrition and health. Geneva. World Health Organization.

These include reports from studies of Keshan disease, Kaschin-Beck disease, and specific studies of cretinism, hypothyroidism, and HIV and AIDS where clinical outcome or prognosis has been related to selenium status. This report and the report by the World Health Organization (WHO), FAO, and IAEA (86) use virtually identical approaches to derive their estimates of basal requirements for selenium (basal R Se ). 

As yet there are no published reports suggesting that these basal estimates using Se or GSHPx activity as criteria of adequacy are invalid. Some modification is necessary however to estimate population minimum intakes with adequate allowance for the variability (CV) associated with estimates of the average selenium intakes from the typical diets of many communities. In the WHO-FAO-IAEA report (86) a CV of 16 percent was assumed for the selenium conventional diets and 12.5 percent for the milk-based diets of infants to limit the risks of inadequacy arising from unexpectedly low selenium contents.

47. World Health Organization. 1998. Complementary Feeding of Young Children in Developing Countries \\WHO/NUT/98.1. Geneva, WHO. 

More recent studies suggest that the variability of selenium intake from diets for which the selenium content has been predicted rather than measured may be substantially greater than estimated previously (Table 49 [47] and Table 50).