Any product containing selenite however should be avoided. Search on “Dietary selenium supplementation modifies breast tumor growth and metastasis” for a study showing that selenium supplementation reduces and delays breast cancer metastasis but that the wrong type of selenium (such as selenite) may exacerbate it.

However, most of us need selenium. Some say selenium is the most potent immune stimulator of all – and it can kill both cancer cells and bacteria. It’s also a great antioxidant and is important for thyroid function.

Selenium supplements are safer when in organic form whereas most selenium products are inorganic and/or synthetic. Dr Mark Sircus in his excellent book “Selenium Medicine” tells us:

The L-selenomethionine form is better absorbed and used by the body than any other known form of selenium – avoid the DL-selenomethionine and the D-selenomethionine which are much less bioavailable. The better forms have better absorption and bioavailability. For example, L-selenomethionine has 3 times the bioavailability of sodium selenite and sodium selenate which are cheaper and therefore more commonly sold as selenium.

Selenomethionine, selenocysteine or mixtures of organic forms found in brewer’s yeast (saccharomyces cerevisiae) are safer. Recent research indicates that with those forms, it’s safe to take higher doses of selenium and this may have additional anti-cancer activity.

The Innate Response selenium has more than 100 times the availability of selenomethionine. Sircus also mentions SelenoPrecise as a very good product and a US$100 product (Selenium Tung Oil 1 oz from Health Solutions) as selenium that can safely be taken in high doses.

Selenium supplementation in those with iodine deficiency can make things worse. Selenium is synergistic with iodine and vitamins C & E so works better when all 4 are taken (but vitamin C works well only with selenomethionine and organic selenium containing yeasts).