Selenium: Functions and Uses

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Selenium: Functions and Uses JoAnn Guest Jun 13, 2005 18:04 PDT

 

 

http://www.willner.com/article.aspx?artid=182

Selenium

Selenium is present in all the tissues of the body, but is concentrated

most highly in the kidneys, liver, spleen, pancreas, and testes. People

do not consume enough selenium both because of the type of diet they

eat, and because of the low selenium content of the soil in which their

food is grown. The selenium content of soil varies widely, with many

areas showing serious depletion. In fact, there have been several

reports of selenium deficiencies in livestock raised on

selenium-depleted soil.

 

FUNCTIONS AND USES

 

Cancer

 

Selenium’s best-known and perhaps most important biological function

relates to its role as an antioxidant and anticancer mineral. As we have

seen in other chapters, free radicals damage our cells, possibly leading

to the development of cancer and other degenerative diseases. Selenium

is an activating component of the enzyme glutathione peroxidase, which

protects our cells from this damage.

 

Many animal studies have proven that selenium deficiency increases the

incidence and rate of growth of cancers in animals that are either

exposed to a variety of potent carcinogens or receive transplanted

tumors. Companion studies have shown that high selenium intake protects

against these cancers. For example, in one study in which rats were

exposed to a potent carcinogen, only 15 percent of those who were also

given selenium developed liver cancer as compared with 90 percent of the

unsupplemented rats. In another study, the occurrence of cancer was 10

percent in the supplemented group versus 80 percent in the control

group. In yet another animal study, selenium supplementation reduced

colon cancer incidence by more than 50 percent. In another study,

selenium protected against UV-induced skin damage and cancer, retarding

the onset and number of skin lesions, and reducing inflammation,

blistering, and pigmentation.

 

In. humans, there is ample epidemiological evidence that high selenium

is correlated with a lower incidence of many types of cancer. For

instance researchers have found that cancer risk is significantly lower

in people living in areas with selenium-rich soil, in people with a

high-selenium food supply, and in people with higher blood levels of

selenium, when compared with people with lower intakes and blood levels.

Selenium intakes in the people studied were close to 750 micrograms per

day, with no toxic side effects noted. In a survey that spanned

twenty-seven countries, including the United States, it was found that

the cancer death rate was lower in those people whose typical diets were

high in selenium. This and other cancer studies indicate that selenium

is especially protective against cancer of the breast, colon, and lung.

Data also suggests protection against tumors of the ovaries, cervix,

rectum, bladder, esophagus, pancreas, skin, liver, and prostate, as well

as against leukemia.

 

 

 

Since 1969, it has been known that the blood levels of cancer patients

are low in selenium. In general, cancer patients with lower-than-average

selenium levels have a greater number of primary tumors, more

recurrences, more distant metastases (tumors that have spread to distant

parts of the body), and a shortened survival time. In a study of 12,000

people conducted in Finland, the risk of fatal cancer in people with the

lowest levels of serum selenium was nearly six times higher than that in

people with the highest selenium concentrations.

 

Like other nutrients, of course, selenium cannot do its work alone. In

several studies, it has been shown that selenium and vitamin E-and

perhaps vitamin A, too—have a synergistic effect. For example, in one

study, male smokers who died of cancer had lower levels of serum

selenium, vitamin A, and vitamin E, when compared with healthy control

subjects. It is well known that vitamin E enhances the antioxidant

effect of selenium. In. addition, it has been found that supplementation

with selenium alone and with selenium plus vitamin E in excess of the

RDAs stimulates the immune system in experimental animals. This effect

is particularly pronounced when the diet is high in polyunsaturated

fats-a factor that has been linked to a higher incidence of certain

cancers.

 

These studies show promise for the prevention and possible treatment of

cancer with selenium supplementation. When combined with other

supplements, the anticancer effect may be even greater. The National

Cancer Inistitute is conducting ongoing " chemopreventive " trials of

several individual nutrients, including selenium, vitamin E, and vitamin

A. However, often these trials are limited to 200 micrograms of selenium

per day, which may be too low a dose to assess the potential protective

effect of this mineral. Larger doses of selenium have been shown to be

protective in animals, and safe in humans. In addition, we are not sure

of the extent to which selenium supplementation influences the later

stages of cancer development. If its influence is strongest in the early

stage, it will be very difficult for these trials to prove the

connection between low selenium and cancer because of the long latency

period for most cancers. (For example, it may take up to fourteen years

for a single breast cancer cell to multiply and produce a tumor large

enough to be detected by currently available diagnostic methods.)

Finally, evidence of the synergism of nutrients has led many researchers

to emphasize the need to consider several nutrients in any given diet

and cancer study, instead of focusing on just one nutrient per study.

 

Cardiovascular Disease

 

In humans, a link has been found between selenium and heart disease.

People found to have overt selenium deficiencies-alcoholics with

cirrhosis of the liver, and people receiving long-term intravenous

feeding-have also been found to suffer from heart problems that respond

to selenium supplementation. In eastern Finland, which has one of the

highest mortality rates from heart disease in the world, it was found

that low selenium in the blood was associated with up to a six- or

sevenfold increase in the risk of death from heart disease. In addition,

children in certain areas of China in which the selenium content of the

soil is low are known to develop a heart disease called Keshan’s

disease. Their heart problems, too, respond to selenium supplementation.

 

Other Functions

 

There is some evidence that selenium may also prove effective in the

treatment or prevention of several other disorders. A study using 400

micrograms of selenium and approximately 25 international units of

vitamin E markedly improved skin conditions such as acne and seborrheic

dermatitis in the test subjects. A Danish study examined patients with

rheumatoid arthritis and found that they had lower levels of selenium.

Those with the lowest levels had the more severe form of this disease.

Moreover, a recent study conducted in Japan suggests that selenium and

vitamin E may enhance the responsiveness of arthritis patients to

conventional treatment. A fascinating study conducted in Scandinavia

showed a correlation between low selenium levels and the incidence and

severity of muscular dystrophy; one patient who was treated with

selenium supplements showed considerable improvement after one year.

Finnish researchers have also conducted a study on elderly patients, who

were given large doses of selenium and vitamin E for one year. After two

months, researchers found an obvious improvement in their patients’

mental well-being, including less fatigue, depression, and anxiety, and

more mental alertness, motivation, and self-care. Finally, selenium has

been shown to protect against the toxic effects of mercury, arsenic, and

copper.

 

RDIs AND DEFICIENCY SYMPTOMS

 

Selenium deficiency symptoms may include muscular weakness and

discomfort. Recent studies have shown that people with celiac disease-an

inborn inability to digest glutenare at high risk for low selenium,

along with other nutrients, either because their lowgluten diets are

also low in selenium, or because of their absorption problems. Down’s

syndrome patients have also been found to have low levels of selenium

and other antioxidants.

 

In one study, refinery workers were found to have low selenium levels in

spite of their dietary intake of 217 micrograms per day, which is more

than three times higher than the RDI. This study indicates that because

of the workers’ exposure to free radicals on the job, their bodies were

utilizing large amounts of selenium to produce the protective enzyme

glutathione peroxidase. This suggests that exposure to toxic

environmental chemicals increases the requirement for this mineral.

 

The RDI for selenium is 70 micrograms for all men and women.

 

Food Sources: There are no accurate available measurements of the

selenium content of foods. However, it appears that the richest sources

of selenium are seafoods, meats, and organ meats-if the animals of

origin ate a diet high in selenium. Whole grains can be good sources,

but, similarly, this depends on the selenium content of the soil in

which they were grown. Fruits and vegetables generally contain very low

amounts of selenium.

 

The refining process strips foods of much of their selenium content. In

one study, it was found that a highly refined diet contains 61 percent

less selenium than does a diet rich in unrefined foods. Cooking also

reduces the content significantly, especially if the cooking water is

discarded. Vitamin C seems to enhance the absorption of selenium.

 

SUPPLEMENTS

 

Selenium is most often available as an individual supplement, although

some multivitamin-mineral formulas are beginning to include this

mineral. I recommend selenium in the form of selenomethionine, which is

extracted from selenium-rich yeast or ocean plants. This form is the

least toxic and appears to be the most absorbable.

 

OPTIMUM DAILY INTAKE-ODI

 

For optimum general health, the basic Optimum Daily Intake for selenium

is:

 

 

 

100-400 mcg for men and women living in low-selenium areas

 

(this includes coastal areas and glaciated areas)

 

50-200 mcg for men and women living in high-selenium areas

 

 

 

The above is excerpted from the book The Real Vitamin & Mineral Book, by

Shari Lieberman, Ph.D and Nancy Bruning, Avery Publishing, 1997

 

 

 

 

AIM Barleygreen

" Wisdom of the Past, Food of the Future "

 

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