Written by Gabriele Dennert and the CAM-Cancer Consortium.
Updated October 20, 2013

Selenium prevention

Abstract and key points

  • Selenium is nutritionally essential for human health.
  • Evidence from two systematic reviews of randomised controlled trials does not support the use of selenium supplements for cancer prevention in populations with an adequate baseline selenium status.
  • Selenium is toxic in high doses and might have adverse effects when taken at supranutritional doses for longer periods of time.

This summary is currently (April 2016) being updated, the version published here was last updated in OCtober 2013. 

The trace element selenium is a nutrient essential to human health and occurs naturally in a variety of foods. Inorganic forms (e.g. sodium selenite or selenate) and organic forms (e.g., selenomethionine) are both used in large numbers of selenium-containing medications, nutritional supplements or dietary aids that are promoted for medical or health purposes. These may contain either selenium alone (mono-supplements) or selenium in combination with other trace minerals as well as vitamins. Supplemental selenium has been advocated as an aid to cancer prevention.

Two recent systematic reviews have evaluated the preventive efficacy of selenium mono-supplements for cancer. Both reviews concordantly found no preventive effect of selenium for non-melanoma skin cancer and prostate cancer; one reported no preventive effect of selenium against stomach, colorectal, oesophageal or lung cancer. The two reviews disagreed regarding the evaluation of selenium for liver-cancer prevention: while one review reported a preventive effect (based on five studies), the other reported no strong indication of a preventive effect (based on three studies).

Although a number of health problems have been linked to selenium deficiency, selenium is also toxic in large doses. The safety of long-term intake of nutritional doses is a controversial issue, which continues to be discussed. Long-term supplementation has caused symptoms of chronic overexposure and has also been linked to increased risks of developing type 2 diabetes mellitus in two randomised clinical trials.

Citation Gabriele Dennert, CAM-Cancer Consortium. Selenium prevention [online document]. http://ws.cam-cancer.org/The-Summaries/Dietary-approaches/Selenium-prevention. October 20, 2013.


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