SELENlUM, a mineral long feared for its toxicity, is on the road
to becoming a Cinderella nutrient. As the last of 40 nutrients
to be proved essential to human health, selenium is now the
subject of both human and animal studies that suggest
it can help prevent the two leading killers in the
Western world: heart disease and cancer. It may
also lift the human spirit.
In the latest published study, selenium supplements
taken for 10 years failed in their primary mission,
to protect against the development of skin cancers,
but they were incidentally found to reduce other
cancers by a third and to cut overall cancer
deaths in half. This effect of a daily 200-microgram
supplement was so dramatic that the researchers
are convinced that it is real, not just a
statistical fluke, even though the study
was designed to examine a different question.
Earlier studies had linked low dietary intakes
of selenium to an elevated risk of heart attacks,
strokes and other diseases related to high blood
pressure. People with low levels of selenium in
their blood were shown to be three times as
likely to die of a heart attack as those with
higher selenium levels, a finding that may be
related to selenium's apparent ability to
raise blood levels of HDL, the "good" cholesterol,
which helps protect against heart disease.
Improvements in well-being have also been noted
in selenium studies. In a 15-week study by
Dr. James G. Penland, a psychologist at the
Grand Forks, N.D., Human Nutrition Research
Center of the Agricultural Research Service,
15 men fed a selenium-rich diet reported a
significant improvement in mood, feeling more
clearheaded and elated at the end of the study
than at the start. A comparable group of men
given a selenium-poor diet reported feeling
worse. The test diet contained 240 micrograms
of selenium daily, more than triple the currently
recommended amount.
But researchers, though optimistic, remain very
cautious about advising Americans to start
gulping down selenium tablets. They point
out that in industrialized countries, where
foods come from many areas, it is possible
to consume amounts of selenium that appear
to be protective as part of a wholesome diet.
And selenium in foods appears to be used better
by the body than the form found in most supplements.
While the promise of benefit from a daily supplement
is strong, it has not been proved, and the possibility
of toxicity for those who overdo it is serious indeed.
Early in this century, thousands of cattle, horses
and sheep in Wyoming, Utah, Nebraska and South Dakota
were felled by two seemingly unrelated conditions
called "alkali disease" and "blind staggers.
The cause in both cases was traced to too much
selenium; the animals had eaten grasses and grains
loaded with the mineral, which is unevenly deposited
in the earth's crust. There are high levels in the
soils of most states west of the Mississippi and
low levels in the Northeast and Northwest and in
some Southeast and Great Lakes states. The same
uneven pattern persists worldwide.
Dr. Gerald F. Combs Jr., a professor of
nutrition at Cornell University, said that
in more than a dozen mountainous provinces
in China where the soil is very low in selenium,
many children developed a potentially fatal
form of heart disease called Keshan disease or
a growth-disrupting joint disorder called
Kaschin-Beck disease.
But selenium's importance in the diet was not
recognized until 1957, when researchers at the
National
Institutes of Health found that selenium could
prevent liver damage in laboratory animals who
were deficient in vitamin E. Subsequent studies
found that small amounts of selenium could even
cure some serious muscle and blood diseases in
farm animals deficient in both vitamin E and
selenium. Finally, in 1969, studies in rats
found that otherwise wellnourished animals,
when deprived of selenium, suffered hair loss,
cataracts and growth and reproductive problems.
Selenium at last joined the list of nutrients
considered essential to animal health, leading
ultimately to its inclusion as one of the
nutrient minerals needed in the human diet
in trace amounts. The Food and Nutrition
Board of the National Academy of Sciences
considers a daily intake of between 50 micrograms
and 200 micrograms to be safe and adequate and
it has established recommended dietary amounts
of 55 micrograms daily for adult women and
70 micrograms for adult men. For infants
and children up to age 14, recommended
daily dietary amounts range from 10 to
45 micrograms daily.
Still, justifiable fears of toxicity have
persisted. In 1984, at least 11 people
were poisoned by selenium supplements
that were accidentally manufactured to
contain 125 times as much selenium as
the Food and Nutrition Board deems to
be safe and effective. Those affected
suffered loss of hair and fingernails,
nausea and vomiting, and fatigue. Similar
toxic effects have been seen in people who
took only 25 times the recommended amount
of selenium.;
Most Americans seem to consume enough selenium
in their food to satisfy the current recommendation
Surveys have indicated that the average American
consumes about 100 micrograms of selenium daily,
although in one study in Maryland, 17 percent of
adults took in less than 50 micrograms. Selenium
tends to be richest in foods high in protein.
Fish, for example, is an excellent source. However,
the main sources of selenium in the American diet
are meats poultry, fish, cereals and other grains.
Among vegetables, mushrooms and asparagus are good
sources. Brazil nuts, especially those sold with
their shells on, are loaded with selenium;
two nuts a day can more than meet the daily need.
Some experts fear that vegetarians who refrain
from eating fish as well as meat and poultry may
have difficulty consuming enough selenium.
The question now, though, is how much is enough.
Selenium is an antioxidant that can help to prevent
the degradation of fats and cell membranes and block
the action of cancer-causing chemicals. More than
100 studies conducted in laboratory animals treated
with carcinogens have shown that selenium added to .
the animals' usual diet protected them against a
number of cancers, including cancers of the breast,
esophagus and liver.
Last month, a study directed by Dr. Larry C. Clark
at the University of Arizona found that 600 people
who took daily supplements of 200 microrams of
selenium (in effect, tripling their normal daily intake)
for 10 years developed 71 percent fewer prostate cancer ,
67 percent fewer esophageal cancers, 62 percent
fewer colorectal cancers and 46 percent fewer
lung cancers than did a comparable group of
600 people who took a look-alike placebo tablet.
No toxic effects of the selenium supplements were noted. -
The tablets used in the study contained
selenium-enriched yeast, prepared by growing
yeast in water spiked with selenium. This organic form
of selenium is the kind found-in foods, whereas most
selenium supplements currently sold consist of
inorganic selenium, which may not have the same effect.
There is also a concern that selenium might
encourage the growth of some cancers. In an
earlier study conducted by Dr. Clark of cancer
rates and the levels of selenium found in forage
in United States counties, those counties where
the forage contained moderate to high levels of
selenium had lower rates of cancers of the lung,
colon and rectum, bladder, esophagus, pancreas,
breast, ovary and pancreas. But the high-selenium
areas also had higher rates of liver and stomach
cancers Hodgkin's disease and leukemia.
Dr. Charles Hennekens of the Harvard School of
Public Health said the new finding "should be a
message to researchers, not the general public."
He added, "It is premature to start taking supplements,
although it may turn out to be the right thing to do."
One important need is for researchers to examine
more closely the interaction of selenium with
other nutrients; raising the intake of one
nutrient may change the demand for another.
Dr. Donald disk, a professor of toxicology at
Cornell and the researcher who discovered the
high levels of selenium in Brazil nuts, noted
that the tablets used in the new cancer study
could be purchased over the counter in drugstores
in dosages of 50 or 100 micrograms. Dr Lisk said
he had analyzed the tablets and found their contents
to be as stated on the label. But he cautioned against
giving any selenium supplements to children and warned
adults against assuming that "if one table is good,
five would be better .
Chief Sources of Selenium in Food
More than 80% of the Selenium in the
American diet comes from just a few foods.
Food % of individual diet Food % of individual diet
Beef 17.2 White Rice 1.7
White bread 14.2 Macaroni & Cheese 1.3
Pork/Ham 8.2 Luncheon meat 1.2
Chicken 6.5 Spaghetti with meat Sauce 1.1
Eggs 4.8 mayonnaise 1.1
White roll 4.0 Meat loaf 1.0 Beef
W.whte bread 3.3 Hamburger on buns 1.0
Noodles 3.0 Oatmeal 1.0
Whole milk 2.8 cracked wheat bread 1.0
Canned tuna 2.1 Rye bread 1.0
2% milk 1.8 Turkey 0.9
Total % 80.3
Source: Gerald F. Combs Jr. Cornell University.
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