History

Selenium is an essential trace element which is normally obtained from the diet. However, it was not until 1979 that it was recognized as a requirement in human nutrition. Previous to this time it was regarded as essential to animals only.

The first major breakthrough was achieved by Dr Klaus Schwartz who discovered that liver necrosis in rats could be prevented with the aid of a kidney extract, found to contain selenium.

As a result of Schwartz' discovery, selenium became the object of an intense programme of research, which continues today. Researchers at Sian University in China in the 60's and 70's experimented with selenium supplementation on sufferers from a heart muscle disease which affected mainly young women and children. The disease is now known as Keshan disease, Keshan being a province in China with the lowest selenium levels in the world. Many people died of the disease, but with the aid of selenium supplementation it has become more or less extinct.

In the 70's selenium deficient agricultural land presented serious problems for the Finnish cattle industry, which were eradicated by the addition of selenium to fertilizers and cattle feed.

General Facts

Selenium has now been discovered to be part of the enzyme system that controls prostaglandins, which have widespread functions in the body. Studies on animals show that selenium reduces high blood pressure and, when combined with Vitamin E, reduces angina pectoris. Selenium deficient animals do not reproduce and in fact half a man's body stores of selenium are found in the testes and seminal glands.

Breast milk contains up to six times as much selenium as cow's milk and twice as much Vitamin E. Australian researchers have linked selenium deficiency to cot deaths.

Effects of Selenium

• Selenium's contribution to the immune system is to protect the cells against damage caused by oxygen-free radicals.

A free radical is an unstable highly volatile and incomplete molecule which is released as a by-product of the body's normal metabolic processes, but which is highly destructive when present in excess amounts.

Selenium is the principal mineral anti-oxidant and free radical deactivator. It combines with glutathione and Vitamin E to form gluathione peroxidase, the body's free radical controller. Other factors include zinc, manganese and copper.

• Prevention of infections and blood clots. It would appear that selenium increases the beneficial prostaglandins (a regulatory factor in the coagulation of the blood) and decreases the formation of harmful prostaglandins (eg prostaglandins causing inflammation in the joints). Low selenium levels are associated with ECG abnormalities indicative of heart problems.
• Selenium prevents cancer. Selenium supplementation has been effective in the prevention of many, but not all, forms of cancer. Selenium alone can give a 50% success rate, but combined with vitamins A & E this rises to a 90% success rate. This incidence of cancer is more common in a sub-group of the population with low selenium blood levels.

As has already been seen, selenium protects cells from damage by oxygen-free radicals. It also decreases the carcinogenic viruses and inhibits the division of cancer cells.

The Link between Vitamin E and Selenium

Selenium is synergistic with Vitamin E, i.e. the beneficial effect of combined selenium and Vitamin E is greater that the added effect of each single nutrient. The enzyme glutathione peroxidase requires both selenium and Vitamin E to function. The most efficient ratio is 100mcg Vitamin E to 25mcg Selenium . (Selenium is 50-100 times more powerful than Vitamin E.)

Sources of Selenium

Good sources include fish, kidney and liver. Whole grains and brown rice may also contain significant proportions, but levels vary, depending on the soil content of the area in which they are grown. However, selenium is also lost in processing. Brown rice has fifteen times higher levels than white rice and wholemeal bread has twice the levels of white bread.

Groups at Risk from Selenium Deficiency

1. Young people who do not eat a balanced diet.
2. Vegetarians - in many cases a vegetarian's daily intake is as low as 10mcg a day - only a fraction more than the daily levels of victims of Keshan disease in China.
3. The elderly - often small meat eaters who do not eat enough to cover their selenium requirement.
4. Pregnant and lactating mothers require much higher levels than is usually ingested with the diet.
5. Smokers generally have lower selenium blood levels than non-smokers. This may either be due to a non-absorption of selenium, or a greater formation of free radicals.
6. The chronically ill - particularly where disease or medication produce loss of appetite, monotonous diets, diarrhoea and vomiting.
7. People living in areas of particularly low selenium levels in the soil, eg China, Scandinavia and Northern Europe.

RDA

There is as yet no Recommended Daily Allowance for selenium in the UK, but the US RDA is 70mcg for men, 55mcg for women, 65mcg for pregnant women and 75mcg for lactating women. However, up to 200mcg can be taken daily and only levels far in excess of this would produce toxic effects.