Taking too much selenium, an essential mineral touted for immune boosting and anti-cancer benefits, could increase cholesterol levels by 10 percent and, as a result, raise the risk of heart disease, a new study suggests.

The findings, published online November 10 in the Journal of Nutrition, a publication of the American Society for Nutrition, warns consumers against taking too much selenium until more research is done to gain a better understanding of the risks and benefits of selenium supplementation.

Study co-author, Dr. Saverio Stranges of the Warwick Medical School in Warwick, England, said the findings of this observational study are “consistent with the findings of earlier clinical work,” which have suggested an association between elevated blood levels of selenium and an increased risk of type 2 diabetes and High cholesterol.

Selenium is a mineral found in grains, nuts, fish and meats. Foods grown and raised in selenium rich environments like the United States have higher natural selenium content than those grown in selenium poor areas, like China.

Not getting enough selenium can contribute to heart disease, an underactive thyroid gland, and a weakened immune system. But, selenium deficiency is rare in healthy populations like the United States where a greater threat may be posed by getting too much.

“If you get more selenium than what you need ... there are no additional benefits and actually there is the potential for adverse effects,” such as an increased risk of diabetes or High cholesterol, Stranges noted in a telephone interview with Reuters Health.

As in the U.S., dietary supplement use is on the rise in the U.K. Stranges and colleagues wanted to know if the findings of previous selenium studies in the U.S. held true for Britain, where people are exposed to less selenium in their environment.

The research team analyzed the 2000 and 2001 diets and health records of more than a thousand British adults. Participants gave blood and answered questions about smoking, drinking, exercise at work and at play, prescription drug use, supplement use, income, and education. Information about physical characteristics such as weight and height was also gathered.

The researchers stopped short of claiming too much selenium causes a boost in cholesterol but wrote that the association between selenium levels in the blood and total cholesterol “was strong,” and consistent with earlier studies.

Cholesterol levels, the researchers found, rose in tandem with blood selenium concentrations.

The researchers caution that the benefits of antioxidants, like selenium, have been aggressively marketed, despite “a lack of definitive evidence on their efficacy for cancer and other chronic disease prevention.”

“We believe that the widespread use of selenium supplements or of any other strategy that artificially increases selenium status above the level required is unwarranted at the present time,” Stranges said in a prepared statement.

SOURCE: Journal of Nutrition 2009.