Common supplements increase prostate cancer risk
Men who take supplements containing vitamin E and a nutrient called selenium may be increasing their chance of prostate cancer, according to a large study from the US.
BMJ Group News
What do we know already?
Prostate cancer usually affects older men. The prostate makes the fluid that carries sperm out of a man’s penis when he has an orgasm. Prostate cancer can happen when cells in the prostate gland grow out of control and invade healthy cells.
Selenium is important in keeping the thyroid gland working properly. Previous research has shown that men with low levels of selenium are more likely to get prostate cancer. Scientists also think that the levels of vitamin E in the body might play a part in how selenium works. So it seemed logical to try to find out if giving supplements of these nutrients to men might reduce their chance of getting prostate cancer.
However, research hasn’t so far provided many clear answers. One large study suggested that vitamin E supplements might have actually slightly increased the chance of someone getting prostate cancer.
To get a clearer picture, researchers in the US carried out a study in more than 35,000 men who were aged at least 50 and did not have signs of prostate cancer. Some men took selenium, some took vitamin E, some took both supplements, and some took a dummy (placebo) for comparison. All men had their selenium levels measured, and researchers compared how many men in each group got prostate cancer.
What does the new study say?
The researchers planned to follow up the men for longer than they actually did. But the study was stopped early, after about six years, when it became clear that more men taking supplements were getting prostate cancer than men taking placebos.
The researchers had expected the men taking supplements to have a smaller chance of getting prostate cancer than the men taking a placebo. But this didn’t happen. The disease was more likely in the group of men taking the supplements that were supposed to reduce the chance of prostate cancer.
Overall, the study found:
- About 5 in 100 men in the study got prostate cancer.
- Men who had low levels of selenium at the start of the study got no benefit from selenium supplements. It didn’t reduce their chance of getting prostate cancer.
- Men who had high levels of selenium at the start of the study who took selenium supplements increased their chance of prostate cancer by 91%.
- Men with low selenium at the start of the study who took vitamin E increased their chance of prostate cancer by 63%.
How reliable is the research?
This was a large study with good methods but, as with most research, we can point to a few reasons to be cautious about its findings. However, when a study is stopped early, as this one was, because of real concerns that people are being harmed, that’s probably a good indication that we should take notice of what it says.
What does this mean for me?
All men want to avoid prostate cancer. But it looks like selenium and vitamin E supplements are not the way to do it. If you are worried about prostate cancer, talk to your doctor. The symptoms can include problems urinating, pain in the back and hip, and painful orgasms. But it’s important to remember that many men with prostate cancer don’t get any symptoms, and that symptoms like pain and problems urinating are common in older men, and they usually don’t mean that you have prostate cancer.