NMA: Nonprescription Medicines Academy

Too Much Selenium May Be Harmful

May 1st, 2012

Although selenium supplementation may be beneficial to people who are deficient in that micronutrient, people with serum or plasma selenium concentrations ≥122 μg/L—including a large proportion of the U.S. population—should not use selenium supplements, according to a review published in Lancet.

Although selenium supplementation may be beneficial to people who are deficient in that micronutrient, people who already have at least adequate intake might be affected adversely and should not take selenium supplements, based on the conclusions of a Lancet. review by Margaret Rayman of the University of Surrey (United Kingdom).

Selenium is a naturally occurring trace mineral found in soil and foods. Selenium obtained from dietary sources or supplements becomes incorporated into selenoproteins that have a wide range of pleiotropic effects, ranging from antioxidant and anti-inflammatory effects to the production of active thyroid hormone. The review summarizes what is known about the effects of selenium on mortality, immune function, HIV and other viruses, neurologic conditions, fertility and reproduction, thyroid function, critical illness, cardiovascular disease, cancer, and type 2 diabetes.

Selenium deficiency has been associated with increased risk of poor immune function, cognitive decline, and death. The available evidence indicates various health benefits— and no extra risk—when people with serum or plasma selenium concentrations <122 μg/L raise their selenium status with supplements to 130–150 μg/L. However, the evidence also indicates that people with serum or plasma selenium concentrations ≥122 μg/L should notuse selenium supplements. This includes a large proportion of the U.S. population.

In particular, the use of selenium supplements by people who already have adequate serum or plasma selenium concentrations might increase the risk of type 2 diabetes.

Lancet. 2012;379:1256-68. Epub 2012 Feb 29.