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IMPORTANCE
OF SELENIUM IN HUMAN HEALTH
Introduction
Selenium
is an essential trace mineral of fundamental importance to human health.
In the
UK over the past 20 years the average
dietary intake has fallen from 60-70 micrograms per day to 30-35
micrograms per day. This has been linked to the switch from using Canadian wheat to
making bread using European grown wheat, which contains much lower levels
of selenium. Even the Canadian
soils have now become depleted by consistent monoculture and the levels of
selenium in Canadian wheat have also dropped significantly over this
period.
The
Government as long ago as 1975 had declared the minimum level of selenium
intake to avoid the impairment of bodily functions to be 75 micrograms
per day for men. Thus selenium is one of the human nutrients in greatest deficiency
and despite its acknowledged importance to human health, selenium is an
essential component of up to thirty proteins that are involved in a wide
range of processes in our bodies, including thyroid hormone metabolism,
antioxidant capacity, fertility, immune function and it may also help to
protect against certain types of cancer and heart disease.
Immune
Function
Cells of the
immune system have important functional needs for selenium.
Selenium deficiency is accompanied by impairment of
immunocompetence, such that selenium repletion can improve the protective
level of our immune systems by as much as twenty to thirty times.
Selenium has been shown to increase the production of antibodies
and selenium deficiency has been linked to the virulence, or disease
progression of some viral infections, including HIV.
A recent (2004) research project, part funded by the FSA, from the University
of Liverpool
found that an increase in selenium intake improves
immune function and poliovirus handling in adults with average (or
deficient) selenium status of the
UK
.
Heart
Disease
Selenium
deficiency may increase the susceptibility to heart disease. Selenium
protects
against arterial deposits and helps to regulate blood pressure.
Selenium supplements have been shown to reduce damage after induced
heart attacks and have been found to reduce heart pain.
In Finland, where there has been a national selenium fortification
programme since 1985, white muscle disease of the heart, which had been a
major problem in livestock farming, has been eradicated.
Heart disease death rates tend to be higher in low-selenium areas.
Cancer
Selenium
helps to protect against cancer by being an essential part of the
important antioxidant systems that protect against free radicals and help
break down carcinogens in the body. Selenium
is also involved in the healthy function of the liver which also
detoxifies carcinogens and in the immune systems, as mentioned previously,
which destroys precancerous cells before they can develop into cancers.
Many
studies since the 1970s have shown that there is an inverse relationship
between selenium intake and cancer mortality between countries.
Residents of cities with low selenium blood levels have higher
cancer death rates.
Selenium
supplementation of cancer patients has improved their survival time after
therapy and studies have indicated that selenium may reduce breast cancer
to 80 percent of its present level. A
study of 34,000 men in the US
found that those subjects with low selenium blood
levels were three times more likely to develop advanced prostate cancer.
A famous trial by Clark in the USA with 1,312 individuals who had
mild skin cancer had to be stopped during the trial as the improved
mortality rates between control and treated was so significant as to
continue would have been unethical. Those
receiving selenium showed 50% lower total cancer mortality and 37% lower
total cancer incidence, with 63% fewer cancers of the prostate, 58% fewer
cancers of the colon, and 46% fewer cancers of the lung. It is interesting to note the control population in this trial
consumed 90 micrograms selenium
per day, well above the UK
average daily intake.
Antioxidants
Selenium
decreases free-radical damage that can accelerate ageing and selenium
supplementation has been shown to increase animal lifespans.
Selenium plays an important role in modulating the damage that
accelerates the ageing process. There
is evidence for a protective effect of selenium in pancreatitis and
asthma, disorders associated with a high level of oxidative stress and a
reduction in pain and inflammation in rheumatoid arthritis. Glutathione
peroxidase, an enzyme that contains four atoms of
selenium, is one of the main antioxidant defence mechanisms in the body,
converting hydrogen peroxide to water.
Selenium
may be critical for body energy level as it has been found that the first
signs of selenium deficiency were the impairment of mitochondrial
function. Mitochondria are
components of human cells that are responsible for the production of
energy.
Evidence
has shown that lifespan correlates to soil selenium levels e.g. Vilcabamba
in Ecuador is a valley rich
in selenium and is widely known as the location of the oldest people on
the planet. In Finland, since the commencement of selenium fortification in
agriculture in 1985, the average age of mortality has increased by ten
years.
Fertility
Selenium
deficiency impairs sperm production and sperm motility, normal sperm cells
contain high levels of selenium. A
study in
Glasgow
found that 11% of subfertile men receiving selenium
fathered a child whilst none did in the placebo group.
Selenium is an essential antioxidant to shield the developing sperm
cells from damage and a selenium compound accounts for about 50% of the
sperm capsule material which confers the structural integrity required for
sperm stability and motility.
A
prominent sign of selenium deficiency in animals is infertility with
supplements significantly reducing early pregnancy loss in sheep.
A human study in the UK found significantly lower selenium blood levels in
women who had had either first-trimester or recurrent miscarriages which
was attributed to reduced antioxidant protection of biological membranes
and DNA due to lack of glutathione peroxidase.
Selenium
is needed for energy production in the mitochondria and fatigue depresses
the sex drive.
Birth
rates in the US
are directly proportional to dietary selenium levels.
Mood
Selenium is
important to the brain as during selenium depletion the brain receives a
priority supply. The turnover
rate of some neurotransmitters is altered by selenium deficiency;
supplementation with selenium has decreased epileptic seizures in
children. Low blood selenium
levels in the elderly were significantly associated with senility and
accelerated cognitive decline and brain selenium levels in Alzheimer’s
patients was only 60% of that in controls. Several studies, including in the UK, have shown that there is a
greater incidence of depression and other negative mood states such as
anxiety, confusion and hostility associated with lower selenium status
that unaffected controls.
Detoxifies
Pollutants
Selenium has
a high affinity for toxic metals, binding onto them and rendering them
harmless, and in foods, selenium binds to pollutants which can prevent
their absorption.
Bioavailability
Selenium supplies from a food source will be a lot more biovailable than
inorganic supplement pills, some research has found this level to be 22
times more available, as the selenium is bound in natural proteins which
can more easily be taken through the gut lining and translocated in the
blood to areas of need. Furthermore,
the low but highly effective concentration of selenium in an enriched loaf gives a lot of
safety to consumers as toxic consumption of pill supplements could be
achieved with just twenty pills, whilst the equivalent intake could only
be achieved by eating nearly 13 loaves in a day.
Summary
There
are 60 trillion cells in the body and each one needs for its functioning
and integrity, the trace mineral called selenium. In some sections of our country, glaciers scraped away the selenium
that plants and the animals that fed on them would have taken up.
In others, intensive cultivation has depleted it.
Demographic and laboratory studies have shown that selenium
deficiency is associated with drastically elevated levels of heart disease
and cancer. Animal breeders
have for decades added selenium to the feed of stock they value - because sterility, early death and stunted growth mean economic ruin.
And
yet, selenium is still not promoted as a vital ingredient for healthy
living and healthy ageing in humans. In
fact, describing the multifarious and disparate roles of selenium make the
mineral seem mystical and unreal. However,
explaining and examining how selenium functions biologically helps restore
credibility to its broad benefits.
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