High selenium linked to diabetes; Americans should stop taking selenium supplements, research team says
By Marla Cone
Editor in Chief
Environmental Health News
May 20, 2009
The research team, led by Johns Hopkins University epidemiologists, examined the diabetes rate and selenium levels of 917 people over the age of 40 who participated in a national health study conducted by the U.S. Centers for Disease Control and Prevention in 2003 and 2004. They found that most had a lot of selenium in their blood, but those with diabetes had substantially more.
The benefits and dangers of selenium have been debated in recent years because some studies show it might help protect people from cancer and heart disease. Selenium is an essential element and antioxidant, but medical experts say there is a fine line between the amount that the body needs and the amount that is harmful.
“Given the current diabetes epidemic, the high selenium intake from naturally occurring selenium in U.S. soil and the popularity of multivitamin/mineral supplements containing selenium in the U.S., these findings call for a thorough evaluation of the risk and benefits associated with high selenium status in the U.S.,” the researchers wrote in a study published online in Environmental Health Perspectives on May 15.
“Furthermore,” they wrote, “our findings suggest that selenium supplements should not be used in the U.S. until there is a better understanding of their potential risks and benefits.”
Supplements containing selenium have gained popularity in the United States because of anti-cancer claims, and selenium levels in people have been rising. Nearly one-quarter of Americans over the age of 40 take selenium supplements or multivitamin supplements that include selenium.
The new findings bolster the concerns of many health experts that extra selenium may be harmful.
The new study was directed by Dr. Eliseo Guallar, an associate professor of epidemiology at the Johns Hopkins University Bloomberg School of Public Health and a director at the National Center for Cardiovascular Research in Madrid, Spain.
One new study, published online Monday in Environmental Health Perspectives, reported that mice exposed to dioxins in utero and then fed a high-fat diet developed higher blood glucose levels. Those fed a low-fat diet, as well as those that were overweight but not fed dioxins, did not have the same health effects. Dioxins are ubiquitous industrial pollutants.
In the selenium study, diabetics had an average of nearly 144 parts per billion of selenium in their blood, compared with about 136 ppb for the non-diabetics. The highest risk of the disease was found for those with levels between 130 and 150 ppb.
Selenium helps the body produce antioxidants and also regulates thyroid hormones. But everyone in the study except for one person had selenium levels that exceeded 90 parts per billion, the maximum amount needed to maintain those healthy functions.
Stern said the only people who should take selenium are those who know they live in low-selenium areas, which are rare in the United States. A U.S. Geological Survey map shows high-selenium soil is scattered throughout the country. In China, however, selenium deficiencies are common so supplements are often necessary.
The recommended dietary allowance for selenium is 55 micrograms per day for adults, and most Americans reach that with diet alone. The FDA warns that the daily intake should not exceed 400 micrograms. The FDA recalled two popular dietary supplements last year that contained more than 40,000 micrograms, an amount considered toxic.
“Given the high selenium exposures in the U.S., the mechanisms underlying these associations need to be investigated,” they wrote.