Dr Sarah Brewer explains all you need to know about the
‘miracle mineral’, Selenium.
Selenium is arguably the most important trace element in our
diet. It forms part of an amino-acid, selenocysteine, which is
found in at least 25 human proteins, including a series of powerful
antioxidant enzymes. As a result, selenium provides protection
against a number of health problems and is especially important for
immunity.
The best food sources of selenium are brazil nuts, fish,
poultry, meats (especially game), wholegrains, mushrooms, onions,
garlic, broccoli and cabbage. Although dietary sources of selenium
should always come first, the lack of it in our food is a growing
cause for concern. During the last ice age, selenium was leached
out of the soil in many parts of Europe, including the UK. While we
used to obtain good amounts from wheat imported from America and
Canada, it is now mainly sourced from within Europe and our
selenium intake fell dramatically between 1978 and 1994 from 60mcg
per day to 34mcg per day - half the recommended amount. The minimum
daily intake to obtain full anti-cancer protection is between 75
and 125 micrograms per day.
Supplements are a good way to boost our shortfall, but for
maximum absorption we need to obtain selenium in a body-ready form,
already incorporated into the amino-acid, selenocysteine. The
best-quality supplements therefore contain selenium-enriched
yeasts, as this form has been shown to be absorbed most readily and
to increase the activity of our antioxidant selenoenzymes more
effectively than inorganic chemical sources such as selenium
selenite. That’s why all the published, placebo-controlled,
cancer-prevention studies have used selenium-yeast supplements.
Selenium-enriched yeast supplements are notoriously
‘smelly’, but look out for lowodour products which,
thanks to new coating technology, are more pleasant to take.
Cancer: Selenium provides one of our most powerful antioxidant
defences against cancer. Taking 200mcg selenium per day has been
shown to reduce the risk of developing prostate cancer by 63%,
bowel cancer by 58% and lung cancer by 46% and to reduce related
deaths by 52%. Results from this trial were so impressive that the
research was stopped early - it was considered unethical to
withhold selenium from those taking inactive placebo.
Stroke: Research involving over 1,110 Finnish males suggests
that selenium helps to protect against stroke. Those with the
lowest levels were almost four times more likely to die from a
stroke than those with the highest. Whether or not it also protects
against coronary heart disease remains uncertain, although it is
possible that the mineral may reduce the risk of non-fatal
attack.
Immunity: Selenium increases the activity of scavenger white
blood cells, involved in the production of antibodies and helps to
reduce the severity of viral illnesses. In one study, people taking
100mcg per day selenium supplements showed a significantly better
response when immunised with live poliovirus vaccine and cleared
the virus from their system more quickly than those taking
placebo.
Asthma: Several studies have found that people with low selenium
levels are more likely to develop asthma. And, in one study, taking
100mcg selenium supplements per day led to a clinically significant
improvement in symptoms.
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subsequent risk of prostate cancer: a prospective cohort study.
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[1] Rayman MP. 2002 The argument for increasing selenium intake.
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[1] Rayman MP. 2004 The use of high-selenium yeast to raise
selenium status: how does it measure up? Br J Nutr.92, 557-73
[1] Rayman M. 2004. The use of high-selenium yeast to raise
selenium status: how does it measure up? British Journal of
Nutrition. 92:557-573
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