The study supports previous evidence of selenium's role on the immune system, vital to protect against diseases like cancer, and also underlines potential problems with the decreasing levels of the mineral in the wheat supply in many European countries.
Research published in 2002 revealed that selenium levels in British bread-making wheats are 10 to 50 times lower than in their American or Canadian counterparts, owing to reduced levels of the mineral in UK soil and lower pollution. Daily intake of the mineral is therefore often lower than the recommended amount in Britain.
Researchers from the University of Liverpool and the Rowett Research Institute in the UK screened adults for plasma selenium concentrations and selected the lowest 60 per cent, or 22 adults with concentrations less than 1.2 µmol/L.
The subjects received 50ug or 100 ug of selenium (as sodium selenite) or a placebo daily for 15 weeks in a double-blind study. Then the whole group was given an oral live attenuated poliomyelitis vaccine after six weeks.
Selenium supplements boosted the immune response, shown by increased production of interferon gamma and other cytokines, an earlier peak T cell proliferation, and an increase in T helper cells, report the researchers in the July issue of the American Journal of Clinical Nutrition (vol 80, no 1, pp154-162).
Selenium-supplemented subjects also showed more rapid clearance of the poliovirus, they said, and an analysis of the faeces of the supplemented subjects revealed a lower number of mutations. This suggests lower potential for disease, according to senior author on the study, Professor Malcolm Jackson.
The data indicate that when the body contains as little selenium as the levels studied here, it could have impaired immune status and find it more difficult to combat viruses, noted the researchers.
They also suggest that even an additional 100 micrograms of selenium daily may be insufficient to support optimal function.
"When we looked at the effects of both 50 and 100ug doses of selenium on the body's selenium pool, most of it was retained, suggesting that we had not yet reached saturation levels," Professor Jackson told NutraIngredients.com.
"This means that we may be able to give even more, particularly as we saw a concentration-dependent effect in the study."
Jackson noted however that maximum total intake levels recently advised by the UK's vitamins and minerals expert group are 450ug. Selenium is thought to be toxic at higher levels, and recent studies on its effects on skin cancer, (which found that it increased the risk of cancer at high doses) appear to back up this safety requirement.
However Professor Jackson added that it is still possible to sufficient amounts of selenium by changing the diet. "We could certainly take it back up to the levels we had 20 years ago by eating different foods."
The Liverpool researchers are currently studying a different form of selenium, the type found in the diet, in a trial funded by the World Cancer Research Fund.