Taking a Selenium supplement may increase your risk of prostate cancer and there is no proven benefit

Dr Ahmed El-Modir

By Dr Ahmed El-Modir

After being diagnosed and treated for prostate cancer, patients often make lifestyle or diet changes they feel may be helpful.

Of course we wholly recognise and support the motivation involved, but it is vital that there is scientific evidence for any major changes.

One area where we currently have concerns is men taking supplements of selenium. Selenium is present in brazil nuts, mushrooms, egg yolks, seafood, poultry and kidney, liver and muscle meats as well as whole grains and seeds.

Scientists first became interested in selenium more than two decades ago, exploring its role in body functions, immunity and possible antioxidant effect.

One study had a huge impact: toenail clippings were analysed from 33,737 men. Levels of selenium could be measured from the clippings and researchers found a link between low levels of selenium and advanced prostate cancer.

But the contention, from this early study, that therefore taking selenium supplements could have a protective role, has not been supported by extensive further research.

The SELECT trial has extensively investigated selenium and prostate cancer, reporting in 2001, 2011 and 2014 and involving many thousands of men.

The most recent results from the 2014 phase have produced two very clear and important findings: there is no evidence of a protective benefit from supplementing selenium AND taking a supplement actually increases prostate cancer risk.

Researchers followed 4,459 men initially diagnosed with prostate cancer from 1988 through to 2010.

Men were categorised according to how much selenium they were taking and during the duration of almost nine years, there were 965 deaths, 23.4% of them due to prostate cancer and 27.7% due to cardiovascular disease.

“Compared with nonusers, selenium supplement users had an increased risk of prostate cancer mortality,” the investigators report. This risk was greatest for the group consuming the highest levels of selenium supplement.

Men who consumed the lowest amount of selenium (1 to 24 mg per day) after being diagnosed with prostate cancer had an 18% higher risk for prostate cancer

This risk of death from prostate cancer increased to 60% among men who consumed 140 mg of supplemental selenium or more per day.

Investigators also analysed the risk for prostate cancer recurrence and selenium supplementation. Analysing 3,718 men, they found there was no benefit in taking selenium and a modest increase from taking a supplement in terms of overall risk of the prostate cancer recurrence.

What can we learn from the results of studies? Research can produce conflicting results and I see many engaged patients who want to be as informed about their condition and active in its management as possible, but find studies that challenge and contradict each other.

The recommended daily allowance (RDA) of selenium in the UK is 75 micrograms for men and 60 micrograms for women. If you follow a good, balanced diet, rich in vegetables, grains and nuts, you will consume a sufficient level of selenium. Supplements often add 100 to 200 mg per day, taking the individual far beyond recommended levels.

What the early “toe clipping” study may reveal is an association between poor diet (thus low selenium levels) and prostate cancer. It does not directly follow however that taking high levels of selenium is protective; indeed it seems to increase risk.

This conclusion is supported by what we know on a microbiological level: Selenium is present in an enzyme called glutathione peroxidase which can act as an antioxidant. However, in particularly high levels, selenium may act as a pro-oxidant (a substance that may cause damage to cells).

We would strongly advise patients do not supplement selenium and follow a good, balanced diet supported by plenty of activity.