Compared to most nutrients, selenium slips by almost unnoticed. But selenium’s relatively low public profile belies this mineral’s important role in optimizing your personal health. Selenium is a part of 25 different compounds known as selenoproteins that are produced by the body; they are necessary to regulate thyroid function, thwart cell damage, bolster immunity and tamp down inflammation.
While there’s evidence that more is not better when it comes to selenium (too much is actually harmful), this diffident nutrient shows promise at moderate supplementation levels for helping to ward off certain illnesses, including some forms of cancer.
Although the final chapter in the selenium story is not yet written, EN sorts out what current research suggests selenium can and cannot do for you.
Avoiding Arthritis. Selenium’s antioxidant properties may help prevent arthritis and reduce its symptoms by quashing the free radicals that can harm healthy joint tissue. University of North Carolina researchers have discovered that low blood levels of selenium are associated with an increased risk of osteoarthritis (OA), especially in women and African-Americans. Their study analyzed the levels of selenium in the toenails of 940 older men and women. (Toenails reflect selenium intake over several years.) People with the highest selenium concentrations were half as likely to suffer from OA as those with the lowest levels.
Honing In on Heart Disease? As part of powerful antioxidant compounds, selenium is capable of preventing the conversion of low-density lipoproteins (LDL or ?bad? cholesterol) to a form that is more likely to clog arteries. In theory, selenium’s antioxidant properties should help head off heart disease.
And in fact, population studies suggest that low levels of selenium in the blood (below 45) may increase the likelihood of heart attack and stroke. In a multi-center study in Europe, toenail selenium levels were linked to risk of heart attack in participants whose levels were the lowest.
However, a recent study led by Saverio Stranges, M.D., Ph.D., from the University of Buffalo, suggests otherwise. Using data from another trial, Stranges and his colleagues evaluated 1,004 men and women and found no link between taking 200 micrograms of selenium a day and a lower risk of heart disease. Clearly, researchers do not have all the answers yet.
Curbing Cancer. Experts are unsure exactly how selenium works to ward off tumors, but it may protect DNA from damage, trigger the self-destruction of cancer cells?often dubbed cell suicide?and boost immunity.
As part of the Nutritional Prevention of Cancer Trial, researchers from the Arizona Cancer Center in Tucson studied the effects of selenium supplements on 1,312 men and women with a history of non-melanoma skin cancers. Half the people received 200 micrograms of selenium daily for an average of four and a half years; the other half received placebos. The supplemented group developed 54% fewer cases of colorectal cancers, 52% fewer prostate cancers and 26% fewer lung cancers.
But the selenium supplements had a downside: They raised the risk of squamous cell skin cancers by 25% and did not protect against recurrent basal cell skin cancers. Squamous cell and basal cell are the two most common forms of skin cancer and are typically curable.
While the findings that link selenium and skin cancer were disappointing, it is critical to keep in mind that the people being studied were already at higher risk for skin cancer, according to Alan Diamond, Ph.D., of the University of Illinois at Chicago. Giving selenium supplements to people without a history of skin cancer might reap different results.
Prostate Protection. Animal studies have confirmed the relationship between selenium and virtually every type of cancer studied, Diamond says. His research has found significantly more prostate cancers in mice bred to produce fewer selenoproteins. Several population studies also support a strong selenium connection.
Recent research pooled the results of 20 population studies and concluded that the higher the selenium levels in the body, the lower the risk for prostate cancer. In addition to helping prevent prostate cancer, this suggests that selenium may also slow its progression.
In another study, Harvard School of Public Health researchers compared blood samples from healthy men later diagnosed with prostate cancer to men who remained cancer-free. The results? Those with the most selenium in their blood were only about half as likely to develop advanced prostate cancer during the 13-year study period when compared to men with the lowest selenium levels. A long-term study sponsored by the National Institutes of Health is currently underway to investigate whether 200 micrograms of selenium a day reduces the risk of prostate cancer in healthy men.
What About Women? The evidence that selenium might help prevent cancer is not as convincing for women. In the Nurses? Health Study, no link was found between toenail selenium levels and cancer risk in 60,000 women ages 30 to 55. One explanation? Perhaps supplemental levels are needed for cancer prevention.
However, in an eight-year French study of more than 13,000 men and women, supplementing with 100 micrograms of selenium a day, plus other antioxidant vitamins and minerals, lowered cancer incidence in men, but not in women.
How Much Is Enough? Adults need 55 micrograms of selenium daily to maximize selenoprotein production. While selenium deficiency is uncommon in healthy people, severe gastrointestinal disorders, such as Crohn’s disease, can result in selenium deficiency. Prolonged infections and inflammation may lead to lower blood levels of selenium as well.
Most adults get all the selenium they need simply by eating a balanced diet, so the question is should you take supplemental selenium? That’s debatable. Extra selenium appears to offer little benefit for heart health, unless you are deficient. And if you?re at risk for skin cancer, you probably should avoid doses of selenium larger than what you would get from a multi. On the other hand, selenium’s prospects for preventing other kinds of cancer are attractive.
University of Illinois? Diamond is hopeful that future studies will show selenium thwarts most, if not all, types of cancer in humans, but cautions that selenium is no magic bullet. ?All selenium can do is reduce the risk of cancer; it can’t guarantee protection,? he says.
Caution When Supplementing. Selenium intake from food generally totals about 100 micrograms a day, on average. (For top sources, see chart below.)
Like all minerals, however, selenium is toxic in large doses. Don’t exceed 400 micrograms per day from foods and supplements, the limit set by the Food and Nutrition Board. If you exceed 400 micrograms a day for a long period, you can develop selenium toxicity. Early signs include brittle nails and hair loss.
If you?re sold on selenium supplements as a cancer preventive, limit your intake to no more than 200 micrograms a day. Selenium as selenomethionine, found in yeast and pill form (and used in the Arizona study), is almost completely absorbed by the body. Sodium selenate and sodium selenite, two other forms, are absorbed somewhat less efficiently.
The Recommended Dietary Allowance for selenium is 55 micrograms
a day. How does your diet stack up?