Selenium
What Is It?
The trace mineral selenium makes its way into our bodies because it is contained in certain foods. Over time, it
becomes part of nearly every cell, with particularly high concentrations in the kidneys, liver, pancreas, spleen,
and testes.
The most concentrated food source for selenium is the Brazil nut; a single one contains 120 mcg, (which is
about twice the RDA). Seafood in general, as well as poultry and meat, are also good sources. So are grains,
especially oats and brown rice.
The concentration of selenium in all these food sources depends on a variable that's very hard for the
consumer to determine: the level of selenium in the soil in which the plant grew (and which the animal then
ate).
Only over the past two decades have scientists begun to understand just what a vital role selenium plays in
numerous biological functions. Perhaps its most crucial job is to prevent disease.
Health Benefits
Selenium has many tasks to perform in the body. It helps to boost the immune system and fight off infection,
providing a general increase in the body's defense against dangerous bacteria, viruses, and cancer cells. On
a basic cellular level, every cell in the body needs a particular hormone from the thyroid gland that selenium
helps to convert to an active form.
Perhaps the most famed use of selenium in supplement form is as an antioxidant; it helps to mop up
dangerous molecules known as free radicals that can damage and alter healthy cells. It has also been
recommended for staving off the effects of aging. In many cases there's relatively weak evidence for these
uses. But not all.
Specifically, selenium may help to:
Prevent cancer. Test-tube studies indicate that in addition to fostering healthy cell growth and division,
selenium discourages the formation of tumors.
When researchers at Cornell University and the University of Arizona pooled results from 5-year studies
designed to assess the effects of selenium supplements (200 mcg daily), they came up with some startling
findings: Compared with the rest of the population, participants had 63% fewer prostate cancers, 58% fewer
colorectal tumors, and 46% fewer lung cancers. Overall, their death rate from cancer was 39% lower than the
average.
Earlier studies had found that in people already diagnosed with cancer, those whose selenium levels were
lowest developed more subsequent tumors than those whose selenium levels were highest. Individuals with
low selenium levels also had a greater likelihood of cancer recurrence, were at higher risk of having the
cancer spread to new organs, and generally survived shorter periods of time.
Protect against heart attack and stroke. Selenium may decrease the "stickiness" of the blood, lessening its
tendency to clot and thus reducing the risk of heart attack and stroke. In addition, the mineral may encourage
healthy heart function by increasing the proportion of HDL ("good") cholesterol to LDL ("bad") cholesterol.
People who have already had a heart attack or a stroke, or who smoke, appear to benefit the most from
selenium.
Guard against cataracts and macular degeneration. Selenium may help prevent the two most common causes
of impaired vision and blindness in older Americans--cataracts and macular degeneration--by providing
antioxidant actions that fight free radicals. It's these free radicals, after all, that often damage the eye's lens
(the site of cataracts) and the macula at the center of the eye's retina (the site of macular degeneration).
Promote healing of cold sores and shingles. When the herpes virus erupts from a dormant state in the body,
painful cold sores and shingles may appear. Selenium, an immune-system booster, may help suppress this
kind of eruption. Interestingly, findings published in Agriculture Research indicate that mice with low levels of
selenium or vitamin E were particularly prone to herpes virus outbreaks.
Fight inflammation associated with lupus. Selenium's antioxidant and anti-inflammatory actions may be
enhanced when combined with vitamin E. For people with lupus, an inflammatory autoimmune disease, this
nutrient duo may foster healing of the skin and help protect the heart, blood vessels, skin, joints, and other
parts of the body prone to inflammation. Along the same lines, the selenium/vitamin E combination may benefit
people with other types of inflammatory disorders too, such as psoriasis, eczema, and rheumatoid arthritis.
Note: Selenium has also been found to be useful for a number of other disorders. For information on these
additional ailments, see our Dosage Recommendations Chart for Selenium.
Recommended Intake
The RDA for selenium is 55 mcg for women and 70 mcg for men. Most adults readily obtain this amount
through their regular diet, and it's rare that people living in an industrialized country become deficient in this
important trace mineral.
If You Get Too Little
Symptoms of selenium deficiency include muscle weakness and fatigue. Poor selenium intake over time may
even increase the risk for cancer, immune-system problems, heart disease, and various inflammatory
conditions (especially skin-related ones).
If You Get Too Much
While many foods are rich in selenium--it's found in grain, meats, seafood, and poultry--you're unlikely to
ingest too much of this trace mineral from your diet.
Taking selenium in concentrated supplement form is a little different, however. Toxic reactions are a risk if you
get an overdose. In one case, people who mistakenly took nearly 500 times the RDA for selenium--from bottles
of 30 mg selenium pills that were erroneously labeled as 200 mcg pills--suffered hair loss, nausea, vomiting,
and fingernail changes. Other signs of potential toxicity include depression, anxiety, and a garlicky odor
emanating from the breath and perspiration.
General Dosage Information
For preventing the effects of aging and protecting against cancer: Take 400 mcg a day.
For guarding against cataracts and macular degeneration: Take 200 to 400 mcg a day.
For cold sores and shingles: During flare-ups, take 600 mcg a day. Don't take more than this amount, and do
not continue for more than a few days.
Be sure to check out our Dosage Recommendations Chart for Selenium, which lists therapeutic dosages for
specific ailments at a glance.
Guidelines for Use
Selenium may be most effective when taken in combination with at least 400 IU vitamin E daily.
For general antioxidant benefits, consider a high-potency antioxidant blend containing selenium along with
vitamins C and E, beta-carotene, grape seed and green tea extracts, alpha-lipoic acid, coenzyme Q10, and
N-acetylcysteine (NAC).
General Interaction
There are no known drug or nutrient interactions associated with selenium.
Cautions
Because of the risk of toxic levels building up in your system, avoid taking high doses--900 mcg or more at one
time, or 600 mcg daily for an extended period of time. Be sure to also take into account the amount of
selenium you're getting from foods.
