Taking too much selenium, an essential mineral said to boost the immune system and offer anti-cancer benefits, could increase cholesterol levels by 10 percent and, as a result, raise the risk of heart disease.

Selenium is a mineral found in grains, nuts, fish and meats. Not getting enough selenium can contribute to heart disease, an underactive thyroid gland, and a weakened immune system. To investigate how an overdose of selenium could affect overall health, researchers analysed the diet and health records of 1042 British adults for two years. The participants gave blood and answered questions about smoking, drinking, exercise at work and at play, prescription drug use, supplement use, income, and education. The researchers also gathered information about physical characteristics such as weight and height.

It was found that cholesterol levels 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.

The findings warn consumers against taking too much selenium until more research is done to gain a better understanding of the risks and benefits of selenium supplementation.

The findings of the study are consistent with earlier findings, which have suggested an association between elevated blood levels of selenium and a higher risk of type 2 diabetes and high cholesterol.