Prostate cancer risk from vitamin E supplements

By Lilian Anekwe

BMJ Group News

What do we know already?

Previous research had suggested that selenium and vitamin E might reduce the risk of prostate cancer. To find out more, researchers studied more than 35,000 healthy men aged 50 years or older, with an average risk of prostate cancer. They were randomly chosen to take either selenium, vitamin E, a combination of the two, or a dummy pill (placebo). The aim was to see how many men in each group had prostate cancer by the end of the trial.

The trial began in 2001, and in winter 2008 the researchers asked the men in the trial to stop taking the supplements because the results showed no benefit, and, instead, showed a possible increase in the risk of prostate cancer for the men taking vitamin E pills. This group did have more men diagnosed with prostate cancer compared to other groups, but because the numbers of cancers were small, the researchers could not tell if the difference was due to chance.

After the trial was stopped in 2008, the researchers continued to record how many men in each group were diagnosed with prostate cancer.

What does the new study say?

The record up until July 2011 shows that more prostate cancers were diagnosed in all three groups of men who took supplements, compared with the number diagnosed in men who took dummy pills. But only the group taking vitamin E showed a difference big enough to be sure it wasn’t down to chance.

There were 529 men in the placebo group diagnosed with prostate cancer, 620 in the vitamin E group, 575 in the selenium group, and 555 in the group taking vitamin E and selenium. For every 1,000 men, there were 76 prostate cancers in men who took vitamin E supplements, compared with 65 in the placebo group.

This difference became apparent in the third year of the trial, and increased slightly each year after.

How reliable is the research?

This research should be very reliable. This is a large study of more than 35,000 men who took part in a randomised controlled trial. This type of study compares the effect of a drug with a dummy pill, or placebo, and is the best way to find out cause and effect. This means we can be sure the difference in the number of men with prostate cancer is due to their different treatments.

Also, the study lasted for ten years. The longer the period of time over which information is gathered, the more confident we can be that the effect is genuine and not due to chance. Also, the effect of taking vitamin E on the risk of prostate cancer began to show as early as the third year. This suggests that the number of men with prostate cancer in the vitamin E group is not artificially high.

The final count of how many men were diagnosed with prostate cancer included those that the researchers had not been able to confirm themselves. This accounted for 17 percent of all the reported prostate cancers, and may have resulted in a small over-estimation of the numbers of cancers.