Overview:
Selenium
is an essential mineral found in small amounts in the body. It works as
an antioxidant, especially when combined with vitamin E. Antioxidants
like selenium help fight damaging particles in the body known as free
radicals. Free radicals can damage cell membranes and DNA, and may
contribute to aging and a number of conditions, including heart disease
and cancer. Antioxidants can neutralize free radicals and may reduce or
even help prevent some of the damage they cause.
Selenium
plays a role in thyroid function and your immune system needs selenium
to work properly. People with a number of conditions, ranging from
rheumatoid arthritis to some types of cancer, often have low levels of
selenium. However, in most cases scientists aren't sure whether low
selenium levels are a cause or an effect of the disease.
When
researchers examined whether selenium had any effect on skin cancer,
they found something unexpected: People who took as little as 200 mcg of
selenium per day for more than 7 years had a significantly higher risk
of developing type 2 diabetes. More studies are needed to understand
exactly what might be happening. In the meantime, you should not take
more than the daily recommended allowance of selenium without your
doctor's supervision.
If you are healthy and eat a well-balanced diet, you should get enough selenium. You may have low levels of selenium if you:
- Smoke cigarettes
- Drink alcohol
- Take birth control pills
- Have a condition that prevents your body from absorbing enough selenium such as Crohn's disease or ulcerative colitis
Heart Disease
The
evidence on taking selenium to treat heart disease is mixed. Scientists
know that low levels of selenium can contribute to heart failure, and
being deficient in selenium seems to make atherosclerosis worse.
Atherosclerosis, or hardening of the arteries, happens when plaque
builds up in arteries, which can lead to heart attack and stroke. But
studies show that taking selenium supplements doesn't seem to have any
effect on the progression of heart disease, nor does it protect against
heart attack.
Selenium,
combined with other antioxidants, including vitamin E and beta-carotene,
may help lower LDL ("bad") cholesterol levels. But selenium can also
interact with cholesterol-lowering drugs (See "Possible Interactions")
and make them less effective. If you have or are at risk for heart
disease, talk to your doctor before taking selenium.
Immune Function
Many
studies suggest that the body needs selenium in order for the immune
system to work properly. Selenium, along with other minerals, can help
build up white blood cells, which boosts the body's ability to fight
illness and infection. A few studies suggest that selenium might help
prevent some infections, such as a bacterial skin infection that often
occurs with lymphedema, and mycoplasma pneumonia. In addition, one study
suggested that when elderly people took zinc and selenium supplements,
their immune systems responded better to the flu vaccine than those who
took placebo.
Asthma
Evidence
suggests that people with asthma tend to have low blood levels of
selenium. In a study of 24 people with asthma, those who took selenium
supplements for 14 weeks had fewer symptoms compared to those who took
placebo. But in a larger randomized, double-blind, placebo-controlled
study, people who took a yeast supplement that contained selenium didn' t
have any fewer symptoms than those who took placebo. More studies are
needed.
Male Infertility
Selenium
and other antioxidants play an essential role in how your body makes
certain proteins found in sperm. One study suggested that selenium
supplements might improve male fertility in men who had low levels of
selenium. However, high levels of selenium are associated with decreased
sperm motility.
Rheumatoid Arthritis (RA)
Low
levels of selenium in the blood may be associated with increased risk
of RA. But it doesn't seem that selenium supplements help once you have
RA.
Dietary Sources:
Brewer's
yeast and wheat germ, liver, butter, fish (mackerel, tuna, halibut,
flounder, herring, smelts) and shellfish (oysters, scallops, and
lobster), garlic, whole grains, sunflower seeds, and Brazil nuts are all
good sources of selenium.
Selenium levels in food depend on how much selenium was in the soil where the food was grown.
Selenium
is destroyed when foods are refined or processed. Eating a variety of
whole, unprocessed foods is the best way to get selenium in your diet.
Available Forms:
Selenium
may be taken as part of a vitamin-mineral supplement, a nutritional
antioxidant formula, or as a separate supplement. Most supplements
contain a form of selenium called selenomethionine.
