Q:I was watching RTÉ news a few days ago and it was reported that selenium and vitamin E do not prevent prostate cancer.
This seems completely different from what I read a few years ago where men were being advised to take these substances to help decrease the chances of prostate cancer. Can you please clarify this for me as I am a little confused?
A:You are correct in what you say about previous reports and this has left people confused as to the benefits of vitamin supplements for prostate cancer. A number of trials had suggested that taking vitamin C and E and selenium could cut the risk of certain cancers including prostate cancer by boosting levels of beneficial antioxidants which work to minimise damage in the tissues, but the results were mixed. A report in the New England Journal of Medicine in 1994 showed that men taking vitamin E had a reduced chance of developing cancer, however, a later report on the same group of men showed no benefit when these patients were followed for a longer period of time.
Recent studies have come out with more definitive results, by involving large numbers of volunteers.
Two large trials were set up in the United States due to the previous evidence suggesting the beneficial effects but one study of 35,533 men, and a second of 15,000 doctors, found no evidence that cancer rates were any lower in those taking supplements. Both studies were published in The Journal of the American Medical Association (JAMA).
The first of the two studies - the Selenium and Vitamin E Cancer Prevention Trial (Select) - found that vitamin E or selenium supplements, whether taken alone or in combination, appear not to reduce the risk of prostate cancer.
In this study, researchers from University of Texas and the Cleveland Clinic Lerner College of Medicine gave healthy men either the trace mineral selenium, vitamin E, both or a dummy pill. The team intended to monitor all the participants for at least seven years but the trial was stopped early because the results were so disappointing. The researchers found there were no statistically significant differences in the numbers of men who developed prostate cancer in the four groups. In all cases, the proportion of men diagnosed with prostate cancer over a five-year period was 4-5 per cent.
In the second study, researchers at Boston's Brigham and Women's Hospital tested the impact of regular vitamin E and C supplements on cancer rates among 14,641 male doctors. Over eight years, taking vitamin E had no impact at all on rates of either prostate cancer, or cancer in general. Vitamin C had no significant effect.
The results are clearly disappointing in that it would be great if dietary supplements could decrease the chance of developing cancer. These findings are disappointing news for the significant number of men who take vitamin supplements - many in the hope of warding off illness. They appear to refute earlier observational studies that linked use of vitamins E and C with reduced risk of certain forms of cancers, including cancer of the prostate.
Dr Jodie Moffat, of the charity Cancer Research UK, says: "There are a lot of studies looking at whether vitamin and mineral supplements can reduce the risk of cancer but many of them, like this one, don't support a link.
"This new research means it is even less likely than we previously thought that supplements can protect against prostate cancer.
"It may be time to give up the idea that the protective influence of diet on prostate cancer risk can be emulated by isolated dietary molecules given alone or in combination to middle-aged and older men," Peter Gann of the University of Illinois at Chicago reflects in a JAMA editorial.
Until that next generation of trials, "physicians should not recommend selenium or vitamin E or any other antioxidant supplements to their patients for preventing prostate cancer", says Gann.
The European School of Oncology also believes that current evidence is not sufficient to advise an increase in vitamin E intake. "Routine vitamin E supplementation cannot be recommended for all men . . . in fact, some studies have shown more deaths from strokes in those groups taking vitamin supplements."
Supplements don't substitute for a healthy diet and it is often recommended that reducing the amount of saturated fat eaten, keeping weight under control, and increasing the intake of fruit and vegetables can reduce the chances of developing prostate cancer.
• This weekly column is edited by Thomas Lynch, consultant urological surgeon, St James's Hospital, Dublin