Common uses include cancer and shedding
Selenium is a trace mineral that our bodies use to produce glutathione peroxidase, an enzyme that serves as a natural
antioxidant. Selenium is also required for normal pancreatic
function and lipid absorption. Glutathione peroxidase
works with vitamin E to protect cell membranes from damage
caused by dangerous, naturally occurring substances known
as free radicals. Adequate amounts of selenium can spare vitamin
E, and adequate amounts of vitamin E can reduce the
selenium requirement. By ensuring that pets receive adequate
amounts of both E and selenium, these important nutrients
will not be deficient and will work together to help fight oxidative
damage in your pet’s body.
Selenium also has an important role in maintaining normal
levels of thyroid hormones and in the metabolism of iodine,
which is involved in thyroid hormone metabolism. Supplementing
the diets of pets and plant enzymes can increase
the selenium levels.
Therapeutic Uses
Many pets with excessive shedding will show decreased shedding
as a result of enzyme supplementation. This may occur as
a result of increased selenium levels and the impact selenium
has on thyroid hormones.
In pets selenium is often prescribed (along with other antioxidants)
for pets with a variety of disorders, including epilepsy,
inflammatory bowel disease, feline leukemia, feline immunodeficiency
virus and cancer.
There is some real evidence that selenium supplements
can provide some protection against several types of cancer.
This chemopreventive effect isn’t fully understood. It might be
due to the protective effects of the antioxidant glutathione peroxidase,
but other explanations have also been suggested.
In people, selenium has been recommended for cancer
prevention, AIDS, acne, cataracts, heart disease, multiple sclerosis,
cervical dysplasia, asthma, rheumatoid arthritis, anxiety,
gout, infertility in men, psoriasis, and ulcers.
Treatment with corticosteroids may induce selenium deficiency;
supplementation may be recommended in pets receiving
long-term corticosteroid therapy.
Scientific Evidence
A large body of evidence has found that increased intake of selenium
is tied to a reduced risk of cancer. The most important
blind study on selenium and cancer in people was a doubleblind
intervention trial conducted by researcher at the University
of Arizona Cancer Center. In this trial, researchers saw dramatic
declines in the incidence of several cancers in the group taking
selenium. The selenium-treated group developed almost 66
percent fewer prostate cancers, 50 percent fewer colorectal cancers,
and about 40 percent fewer lung cancers as compared with
the placebo group. Selenium-treated subjects also experienced
a statistically significant (17 percent) decrease in overall mortality,
a greater than 50 percent decrease in lung cancer deaths, and
nearly a 50 percent decrease in total cancer deaths.
Further evidence for the anticancer benefits of selenium
comes from large-scale Chinese studies showing that giving selenium supplements to people who live in seleniumdeficient
areas reduces the incidence of cancer. Also, observational
studies have indicated that cancer deaths rise when
dietary intake of selenium is low.
The results of animal studies corroborate these results.
One recent animal study examined whether two experimental
organic forms of selenium would protect laboratory rats
against chemically induced cancer of the tongue. Rats were
given one of three treatments: 5 parts per million of selenium
in their drinking water, 15 parts per million of selenium or placebo.
The study was blinded so the researchers wouldn’t know
until later which rats which treatment. Whereas 47 percent of
rats in the placebo group developed tongue tumors, none of
the rates that were given the higher selenium dosage developed
tumors.
Another study examined whether selenium supplements
could stop the spread (metastasis) of cancer in mice. In this
study, a modest dosage of supplemental selenium reduced
metastasis by 57 percent. Even more significant was the decrease
in the number of tumors that had spread to the lungs.
Mice in the control group had an average of 53 tumors each,
whereas mice fed supplemental selenium had an average of
one lung tumor.
Putting all this information together, it definitely appears
that selenium can help reduce the risk of developing cancer.
Sources
Wheat germ, brazil nuts, other nuts, oats, fish, eggs, liver, wholewheat
bread, bran, red Swiss chard, brown rice, turnips, garlic,
barley and orange juice contain selenium. There is some concern
with conventional farming practices that mineral levels in
the soil are inadequate. This means that the soil used for growing
vegetables and fruits may be deficient in minerals such as
selenium. According to information from the Organic View, 1:17
(www.purefood.org/organicview.htm), there is great variability
in the nutrient contents of foods raised by industrial agricultural
practices when compared to organically raised foods. For
example, they report that in an analysis of USDA nutrient data
from 1975 to 1997, the Kushi Institute of Becket, Massachusetts,
found that the average calcium levels in 12 fresh vegetables declined
27 percent; iron levels dropped 37 percent; vitamin A levels
21 percent and vitamin C levels 30 percent.
They also report that a similar analysis of British nutrient
data from 1930 to 1980 published in the British Food Journal
found that in 20 vegetables, the average calcium content had
declined 19 percent; iron 22 percent; and potassium 14 percent.
In addition, a 1999 study out of the University of Wisconsin
found that three decades of the over use of nitrogen in U.S.
farming has destroyed much of the soil’s fertility, causing it to
age the equivalent of 5,000 years. Finally, a new U.S. Geological
Survey report indicates that acid rain is depleting soil calcium
levels in at least 10 eastern states, interfering with forest
growth and weakening trees’ resistance to insects. Findings
such as those reported here prompt many owners to search
for the most wholesome produce available to include in their
pets’ diets.
Check with stores in your area to see whether they offer
organically raised vegetables and animal meats. Also, ask
them what they mean by the term “organically raised,” as many
producers may make his claim but still use conventional agricultural
practices. Find out everything you can about the farmers
who supply the stores where you shop.
Since most of us have no way of knowing what kind of
soil our food was grown in, supplementing pets with selenium
and other vitamins and minerals may be a good idea.
The two general types of selenium supplements are organic
and inorganic. However, these terms have nothing to do
with “natural” but rather refer to the chemical form (the terms
have very specific chemical meanings and have nothing to do
with “organic” foods).
The inorganic form of selenium, selenite, contains no carbon
atoms and is essentially selenium atoms bound to oxygen.
Some research suggests that selenite is harder for the body to
absorb than organic (carbon-containing) forms of selenium,
such as selenomethionine (selenium bound to methionine, an
essential amino acid) or high-selenium yeast (which contains
selenomethionine). However, other research on both animals
and humans suggests that selenite supplements are almost
as good as organic forms of selenium, and both forms are
equally effective in supporting glutathione peroxidase activity.
In pigs, studies have shown that selenium stores in the
liver and muscle tissues were greater when organic selenium
was fed. Supplying selenium in whole food supplements is the
most natural way to supply selenium and is recommended for
maintenance.
Dosage
The AAFCO recommendation is 0.11 mg/kg of food (dry matter
basis) for dogs and 0.1 mg/kg of food for cats. However,
recent research in puppies has shown that the level of dietary
selenium needed to maximize glutathione and selenium levels
is 0.21 ppm, which is double current AAFCO recommendations.
Therefore, supplementation with a natural vitaminmineral
supplement containing selenium might be indicated
for all pets eating commercial diets.
Safety Issues
Selenium is safe when taken at the recommended dosages.
However, very high selenium dosages in people are known
to cause selenium toxicity. Signs of selenium toxicity include
depression, nervousness, emotional instability, nausea, vomiting,
and in some causes loss of hair and fingernails. Similar
precautions are probably warranted in pets taking supplements,
although toxicity has not been noted in pets despite
concentrations greater than 4 mg of selenium/kg of food in
cat foods containing fish or other seafoods. (Cats may be
able to tolerate higher selenium levels as their higher dietary
protein foods are protective against high selenium levels; the
low availability of selenium in pet foods may also contribute
to rare reports of toxicity in dogs and cats fed commercial
diets.)
