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Selenium is a contradictory nutrient. It has been called the essential poison—too
much of it in the diet can be toxic; too little can result in chronic, and sometimes
fatal, deficiency. Even health authorities have at times been confused. Although
today in the USA, as in most other countries, selenium appears among the trace
elements for which recommended dietary allowances (RDAs) have been established,
it was at one time declared by the Food and Drug Administration (FDA)
to be a carcinogen and banned as an additive in food.
Selenium is considered by some to be a serious hazard to the environment and
to animal health. Selenium-contaminated water has brought deformity and death
to wildlife in nature reserves in western USA. There is even concern that because
of selenium contamination of soil, crops supplied to the great cities of California
could become unfit for human consumption. In large areas of China, endemic
selenium toxicity is a hazard for locals who depend on crops grown on seleniumrich
soil. Yet, in the UK, and in other parts of Europe, fears are expressed that soil
selenium levels are inadequate. There are demands that the example of Finland
should be followed and soil selenium levels increased by the addition of selenium
to fertilizers.
There may be controversy among the experts and health authorities about selenium,
but this has not deterred the general public from deciding that the element
has an important role to play in health. In New Zealand, when the use of selenium
was first permitted to prevent deficiency in farm animals, but was still not
approved as a supplement for humans, people took the matter into their own
hands. Veterinary preparations containing selenium were used by those who
believed that what was good for animals must also be good for humans.
Undeterred by reports of their possible toxic effects, today millions of people
worldwide consume selenium supplements. They are encouraged to do so, not
only by articles in the popular media but also by the results of investigations by
reputable scientists which indicate that selenium has a vital role to play in human
health, not least in the prevention of cancer. Their findings indicate that selenium
is a key player in cellular metabolism, is an essential component of enzymes that
protect the body against oxidative damage, and has important roles in thyroid
metabolism, human fertility, and many other vital functions. |