Selenium supplements found harmful

S elenium is a trace mineral that is essential to good health but necessary only in small amounts. Before it was found to be an essential nutrient, selenium was considered remarkably toxic to humans.

Early research was optimistic that selenium supplementation might help prevent cancer and certain cardiovascular problems. A breakthrough occurred in 1973, when a research team observed that selenium protected against oxidative damage in selenium-deficient rats. But recent research has found that selenium supplementation might be more harmful than beneficial to humans.

An international medical research team reported in Annals of Internal Medicine that selenium supplements are likely to increase the risk for diabetes. In this study, 1,202 participants were given either oral selenium or placebo. During a follow-up of over 7 years, type 2 diabetes occurred in 58 of the selenium recipients, but in only 39 of the placebo recipients.

Another study examined the relationship between the use of multivitamins containing selenium and the risk of prostate cancer. The study investigated 295,344 men with a mean age of 62 years who were cancer free at enrollment. The researchers discovered that persons taking high levels of multivitamins containing selenium had increased risks of advanced and fatal prostate cancers.

Yet another study investigated selenium for the prevention of cardiovascular disease. In this trial, over 1,000 subjects were given either oral selenium or placebo. These researchers found no overall effect of selenium on cardiovascular disease.

An international research team conducted a systematic review to investigate the effects of selenium for primary prevention of cardiovascular disease and the potential adverse effect on type 2 diabetes. Over 19,000 participants were involved in the studies reviewed. Selenium supplementation did not reduce all cause mortality, cardiovascular disease mortality, or non-fatal cardiovascular disease events. But it did increase the risk of type 2 diabetes.

Selenium supplementation might be beneficial in certain populations, such as those with HIV or those with severe gastrointestinal problems, such as Crohn’s disease. It may also be beneficial in regions where diets are low in selenium, such China. But there is no selenium deficiency in the United States. So selenium supplementation is a real public health concern. More than 1 percent of Americans take selenium supplements, and more than 35 percent take multivitamin/mineral supplements that often contain selenium.

In light of information that selenium may be associated with increased health risks, caution is recommended. Selenium supplementation should be avoided.