Selenium is one of those micro-nutrients which although required by the body in only tiny quantities are nevertheless vitally important for the health and well-being of the human organism.
There’s now compelling evidence of selenium’s significance as an anti-oxidant, in fighting cancer and heart disease, and as a stimulant for the immune system.
Selenium’s importance as an anti-oxidant lies principally in its necessity for the production of the key anti-oxidant enzyme, glutathione, which forms one of the body’s first lines of defence against dangerous superoxide free radicals. The body particularly needs the fat-soluble glutathione to work with vitamin E to soak up and neutralise any free radicals attacking the delicate yet vital fatty structures of cells such as the membranes.
In this way selenium and vitamin E appear to work so closely together that a deficiency in one may be compensated for by the other, and selenium is also crucial as part of the enzyme thioredoxin reductase which is important in maintaining the anti-oxidant properties of vitamin C. Moreover, vitamin E cannot itself do its work in the absence of an adequate supply of active vitamin C; and vitamin C cannot remain active without the presence of glutathione.
Selenium therefore forms part of a complex web of interacting nutrients, each of which is essential to a successful anti-oxidant rich diet, and whilst the amounts of selenium required by the body may be tiny, the Recommended Dietary Allowance (RDA) being set at just 55 micrograms per day, the effects of any deficiency can be nevertheless disastrous.
It has to be said that a microgram (mcg) is a very small quantity indeed a mere one thousandth of a milligram, so it might seem highly unlikely that anyone in an affluent Western society could allow himself to be deficient. And indeed, a little attention to the daily diet should ensure that this is the case.
The richest food source of selenium, by far, is brazil nuts, and amazingly a single nut may provide as much as 100 mcg. A mere one ounce serving of nuts may yield more than 800 mcg, more than double the Food and Nutrition Board’s recommended upper safe limit of 400 mcg. But luckily both organ meats and seafoods such as shrimps, crabmeat, salmon or halibut may provide selenium in much more manageable amounts of up to 40 mcg in a 3 oz serving. Muscle meats are also a reasonably good source, although pork, the best of these, will only provide around 33 mcg per 3 oz.
Whole grains such as brown rice or wholemeal bread may provide 15-20 mcg per serving, but fruits and vegetables are not particularly useful sources because of the way in which modern intensive farming procedures continue to strip soils of their mineral content.
Nevertheless, most healthy individuals seem to have little difficulty in achieving the RDA. But mere freedom from deficiency disease is not at all the same thing as optimal health. So the question must be: is there likely to be any benefit in supplementing above the 100 mcg level, but below the 400 mcg upper limit?
The answer appears to be a resounding yes. In addition to ensuring the maximum possible supply of vital anti-oxidant enzymes, research strongly suggests that supplementation at the level of 200 mcg per day may act as a stimulant to the immune system and may also help in the fight against cancer, particularly that of the prostate.
Research published in the Journal of the American Medical Association in 1996, although insisting that further studies are needed, suggested that selenium supplements at a level of 200 mcg a day may have a striking effect in reducing certain common types of cancer, including those of the prostate by 63%, oesophagus by 67%, colorectal by 58% and lung by 46%.
Another study of 33,000 men over 5 years demonstrated a 2/3rds reduction in the risk of prostate cancer for men taking 200 mcg a day (Journal of National Cancer Institute 1998), whilst a further study of 9,000 Japanese/American men found a 50% reduction in the risk of developing prostate cancer for those in the highest quartile of selenium intake compared with those in the lowest quartile.
A useful working hypothesis may be that as cancer is principally a disease of degeneration, it is the acknowledged anti-oxidant effect of selenium that is responsible for its apparent effectiveness in this area.
As always, however, the medical establishment is cautious, and reluctant to confirm the potential benefits of nutrition as opposed to more invasive, conventional therapies. But the indications for selenium in relation to prostate cancer, in particular, are so promising that a number of large trials against placebo control are currently in progress.