Selenium and cancer: Friends or foes?

The Bottom Line

  • Previous studies have suggested that selenium supplements might help prevent cancer.
  • Newer research shows that selenium is unlikely to lower cancer risk.
  • Taking selenium supplements may increase the risk of certain types of cancer and type 2 diabetes.

Cancer is all too common, nearly half of Canadians will develop cancer at some point in their lifetime, and one in four will die from the disease (1). So, it’s no surprise that many of us are looking for ways to reduce our risk. Search the internet, and you’ll be flooded with possibilities. One claim that you’re likely to come across is that dietary supplements, including vitamin and mineral supplements, have cancer-fighting abilities. The trick is to figure out which claims are supported by evidence.

Selenium is touted to pack an anti-cancer punch (2). This essential mineral is richly abundant in foods like seafood, organ meats, grains, and dairy products (3). Despite being important to human health, selenium is reported to be toxic when taken at high doses that surpass the level needed to stay healthy. Additionally, a safe range of selenium consumption has yet to be clearly defined (4;5). Many Canadians get the nutrients they need from a healthy and balanced diet, and selenium is no exception (3;6). Even so, two-thirds of women and one-half of men over the age of 70 – add nutritional supplements like vitamins, minerals, fibre, antacids, and fish oils to their diet, hoping that this will give their health an added boost (6).

When it comes to cancer, can selenium supplements help? Past research on the topic has had conflicting results, while recent research suggests that they may do more harm than good (2).

What the research tells us

In the past, studies showed that taking selenium as a supplement helped prevent people from getting cancer. However, a more recent systematic review suggests that this might not be true. This review looked at many different types of cancer – including head and neck, esophageal, colorectal, liver, skin, lung, breast, bladder, prostate, and blood cancer – and found no evidence that selenium supplements reduced cancer risk (2;7). Selenium supplements were also associated with side effects such as an upset stomach (2). What’s more, some studies found that selenium supplements may increase the risk of prostate cancer, skin issues, and type 2 diabetes (2;7). The effects of selenium in people with certain genetic or nutritional backgrounds was not evaluated, but should be a topic of future research (2).

Considering selenium as an addition to your cancer risk reduction routine? You may want to think twice before reaching for this supplement, weighing the potential risks and the lack of evidence to support its use.

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  1. Canadian Cancer Society’s Advisory Committee on Cancer Statistics. Canadian cancer statistics 2017. [Internet] 2017. [cited May 2018]. Available from  
  2. Vinceti M, Filippini T, Del Giovane C, et al. Selenium for preventing cancer. Cochran Database Syst Rev. 2018; 1:CD005195. doi: 1002/14651858.CD005195.pub4.
  3. National Institutes of Health. Selenium. [Internet] 2018. [cited May 2018]. Available from
  4. Jablonska E, Vinceti M. Selenium and human health: Witnessing a Copernican revolution?. J Environ Sci Health C Environ Carcinog Ecotoxicol Rev. 2015; 33(3):328-368. doi: 10.1080/10590501.2015.1055163. 
  5. Vinceti M, Filippini T, Cilloni S, et al. Health risk assessment of environmental selenium: Emerging evidence and challenges (Review). Mol Med Rep. 2017; 15:3323-3335. doi: 10.3892/mmr.2017.6377.
  6. Statistics Canada. Use of nutritional supplements, 2015.  [Internet] 2017. [cited May 2018]. Available from
  7. Cortés-Jofré M, Rueda JR, Asenjo-Lobos C, et al. Drugs for preventing lung cancer in healthy people. Cochrane Database Syst Rev. 2020; 3:CD002141. doi: 10.1002/14651858.CD002141.pub3.

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