Following last week's claims and counter claims that dietary supplements may offer protection from avian flu, Stephen Daniells looks into statements that selenium supplements may offer protection.
Many novel virus have been found in selenium deficient populations, with experts suggesting that relatively harmless viruses can mutate into deadly versions on passing through a selenium deficient host.
This has led some to propose that selenium supplements may offer some kind of protection from the world's newest threat - avian 'flu.
Consumers seem to be taking notice of such reports, with some companies reporting increased sales in light of increased press coverage.
Rita Stoffaneller, senior nutritionist and registrations manager with Wassen International Ltd who offer a range of selenium products, told NutraIngredients.com: "Consumers are increasingly aware of the role of selenium and immune protection. Recent press articles have generated a sales increase of more than 60% across the range in the UK in the last 2 weeks."
The link between selenium and immune system health is backed up by a growing body of science.
Researchers from the University of North Carolina, and the US Department of Agriculture reported that selenium deficient mice infected with a mild strain of influenza developed severe lung infections. When the researchers recovered the virus from the mice, they found an increased number of viral mutations, "resulting in a more virulent phenotype." (Trends in Microbiology, 2004, Vol. 12, pp. 417-423).
"Wide-spread nutritional deficiencies occur in many developing countries, which are frequently the site of emergence of new viral diseases as well as old viral diseases with new pathogenic properties," wrote the researcher.
The increased occurrence of mutated viruses in selenium-deficient individuals has been linked to the antioxidant nature of the mineral. Selenium is included into about 25 selenoproteins, five of which are powerful antioxidant enzymes.
If the host's antioxidant defences are weakened, then the virus is exposed to greater oxidative stress, and thus a greater chance of viral mutations.
Not only have low selenium levels been linked to higher virus mutations, but also to a reduction in the efficiency of the immune system. Selenium deficiency has been linked to reduced T-lymphocyte activity and reduced antibody production.
Dr Margaret Rayman of the Centre of Food Safety and Nutrition at Surrey University has published several articles on the immune boosting activities of selenium (Proceedings of the Nutrition Society, 2002, Vol. 61,pp. 203-215).
"Taking a selenium supplement may make a difference to a person with low selenium status and may help them deal more quickly and effectively with a viral infection. This could reduce their chances of becoming seriously ill," said Rayman.
It would be incorrect and irresponsible to suggest that increasing the selenium intake of populations will eradicate the threat of H5N1. However, like vitamin C and zinc, the mineral could boost the body's natural defences, a view shared by Wassens.
The US Council for Responsible Nutrition recently warned consumers to be wary of supplements being touted as offering protection from avian flu.
In a statement issued in November, the CRN said: "We do not believe that any dietary supplements have been specifically shown to prevent or treat avian 'flu."
Judy Blatman, VP communications for CRN told NutraIngredients-USA.com at that time: "We believe that responsible supplement companies will not take advantage of consumers' fears about avian flu and try and market a product as a remedy for it."
European selenium levels have been falling since the EU imposed levies on wheat imports from the US, where soil selenium levels are high. As a result, average intake of selenium in the UK has fallen from 60 to 34 micrograms per day.
The European recommended daily intake (RDI) is 65 micrograms.
The current market for selenium supplements in Europe is estimated to be worth around €40 million.