Selenium not shown to cause ‘dramatic reduction’ in certain cancers

A Facebook video shared thousands of times contains a claim that selenium is an effective treatment for cancer based on medical research. Unfortunately, this is not the case.

In the video, Dr Peter Glidden, a naturopath, is talking to the camera describing supposed benefits of the substance found in studies. He says that “when [researchers] just used selenium all by itself, dramatic reduction in prostate cancer. Dramatic reduction in lung cancer. It's a remarkable therapeutic agent.”

But the evidence doesn’t show it to be beneficial in preventing or treating the disease.

We have written many times regarding false claims about alternative treatments for diseases, especially regarding cancer. If people delay investigation or treatment of cancer based on bad information, this could have serious consequences.

Full Fact has contacted the Facebook account that uploaded the video but we have not received a response at the time of writing. We also contacted Dr Glidden via social media, but he did not provide us with any evidence to support the claims.

An important trace element

Selenium is an essential trace mineral—something that we need to consume (in tiny amounts) for our body to work normally. It is indeed important for thyroid function as the video says. It is present in many common foods.

It’s unclear whether the video is saying that selenium reduces the risk of developing cancer, or is effective at treating cancer once it exists.

Risk of cancer

The most recent Cochrane review (a review of the existing research generally seen as some of the highest quality evidence in medical science) was published in 2018 and found that “there is no evidence to suggest that increasing selenium intake through diet or supplementation prevents cancer in humans”. This included prostate cancer specifically, which was the cancer most commonly looked at in the studies found. 

The review does note that “more research is needed to assess whether selenium may modify the risk of cancer in individuals with a specific genetic background or nutritional status, and to investigate possible differential effects of various forms of selenium.” 

Results have been mixed but there are also some findings of increased cancer incidence associated with certain genetic changes alongside selenium supplementation. 

In mentioning prostate cancer, the video may be referring to lower quality evidence linking selenium supplementation in people who are very deficient in the mineral with a lower prostate cancer risk. This was noted in an earlier 2014 Cochrane review, but has not been proven by further research.

The video also mentions lung cancer. Memorial Sloan Kettering Cancer Centre (MSKCC), a US cancer research and treatment institution that provides information about alternative treatments, refers to some data suggesting a potential link between selenium and reduced gastrointestinal and lung cancers.

Another 2011 meta-analysis (a piece of research in which a number of studies are pulled together) reported a potential benefit, again in people who had low selenium levels to start with. 

However, the later Cochrane reviews are stronger evidence than this. 

Treating cancer

Larger, higher quality evidence like Cochrane reviews are lacking regarding use of selenium as a treatment. But this doesn’t mean that selenium can be recommended to treat cancer. 

MSKCC says that a trial in lung cancer patients didn’t find any improvement with selenium use.

It also tentatively notes some promising studies looking at selenium to improve symptoms for patients having conventional cancer treatment, but is clear that more research is needed.

What’s the harm?

The latest Cochrane review notes that: “Some trials unexpectedly suggested that selenium may increase risks of high-grade prostate cancer, type 2 diabetes, and dermatological abnormalities”. 

While this isn’t conclusive, there is a risk of possible harm, and promoting selenium as a treatment without being clear about the extent of the evidence (or lack) behind it could damage people’s health.

Featured image courtesy of Muderkind