Summaries for Patients17 May 2011

The Effects of Selenium Supplements on Blood Cholesterol Levels

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      What is the problem and what is known about it so far?

      Selenium is a mineral that is required in very low doses for the body to function normally. It is an antioxidant, meaning that it prevents oxygen from damaging cells and reduces inflammation. These actions have led to speculation that it might also protect persons from chronic diseases that can develop from cell damage and inflammation, such as heart disease and cancer. Many people in North America get enough selenium in their diet. But many other people, particularly those in Europe, do not. Selenium is included in many multivitamins and is sold as a supplement itself, which many persons take to stay healthy. For example, some evidence links low blood selenium levels to heart disease, suggesting that receiving selenium supplements would prevent disease. However, it is not clear if such supplements are entirely safe. Other evidence suggests that high blood selenium levels are associated with higher cholesterol levels, implying that receiving selenium supplements could promote rather than prevent heart disease.

      Why did the researchers do this particular study?

      To assess more precisely the effects of selenium supplements on cholesterol levels.

      Who was studied?

      501 healthy volunteers aged 60 to 74 years in England.

      How was the study done?

      The researchers gave all participants a placebo pill for 1 month to identify who could take the study supplements consistently. They did blood tests to assess blood selenium levels and total, “good,” and “bad” cholesterol levels in each participant. They then assigned the participants who could receive the pills to receive a low, an intermediate, or a high dose of selenium, or they assigned participants to continue receiving the placebo for an additional 6 months. At the end of the 6 months, the researchers measured the change in the selenium levels and in total, good, and bad cholesterol levels in each volunteer to see whether they differed from measures at the beginning of the study.

      What did the researchers find?

      Participants' blood selenium levels were relatively low at the start of the study. Selenium levels increased with supplementation, as was expected. In contrast, total and bad cholesterol levels seemed to decrease by a small amount in each group that received selenium, but not in the group that received placebo. Good cholesterol levels increased very slightly in the group that received the high dose of selenium but not in the group that received low or intermediate doses.

      What were the limitations of the study?

      Study participants were aged 60 to 75 years. The findings might be different for younger persons or those who have a higher intake of selenium. The study lasted only 6 months. Persons often receive dietary supplements for much longer, and the effects of selenium over a longer period are unknown. Cholesterol levels are only 1 factor contributing to heart disease. Selenium may also increase risk for diabetes or be harmful in other ways. The study did not measure the effects of selenium on other diseases.

      What are the implications of the study?

      Receiving selenium supplements does not seem to worsen blood cholesterol levels and may decrease them slightly. The findings are reassuring, but they do not justify the use of selenium supplements as a safe way to treat abnormal cholesterol levels instead of, or in addition, to cholesterol drugs. The reason is that the beneficial effects were very modest, and selenium could be harmful in persons with a high intake of selenium from their regular diet.