Vitamin supplements do not help prevent cancer. A large trial of the potential chemopreventive effect of selenium and vitamin E show that the supplements do not reduce the risk of prostate and other cancers.

Vitamin supplements do not help prevent cancer. A large trial of the potential chemopreventive effect of selenium and vitamin E show that the supplements do not reduce the risk of prostate and other cancers.

 Summary

Prostate cancer is the second leading cause of cancer death in the United States. Therefore, there is keen interest in prevention. The largest trial of its kind, however, now shows that selenium and vitamin E supplements do not prevent prostate cancer so people should not rely on them. Other ways of cancer chemoprevention need to be found.

Introduction

Prostate cancer is a major public health concern, as it causes nearly 30,000 deaths a year in the United States. An effective prevention strategy would, therefore, be very welcome. Previous trials have suggested that antioxidant vitamins like vitamin E could be worth exploring in this respect. Selenium, too, seemed to show some promise. The SELECT (Selenium and Vitamin E Cancer Prevention Trial) which we report on here is probably the biggest cancer chemoprevention trial ever carried out.

What was done

Researchers at the University of Texas MD Anderson Cancer Center and colleagues elsewhere studied a group of 35,533 men aged 50 and over if Afro-Caribbean and 55 or more for others. The participants came from the United States, Canada, or Puerto Rico. They were assigned to one of four groups: selenium (200 micrograms a day), vitamin E (400 IU a day), selenium plus vitamin E, placebo. The trial ran between 2001 and 2004 with a planned follow up time of seven years.

What was found

The trial was stopped early, in 2008, because it was becoming obvious that there was no benefit to taking the supplements. Analysis of the data suggested that it was extremely unlikely that any benefit would emerge if the trial was continued. Rates of prostate cancer were around five percent in each of the four groups. The findings are at odds with previous evidence. The researchers say a different form of selenium was used in the earlier studies but it would have been difficult to get this in a pure enough form for a clinical trials and it raised some safety concerns. Also, the earlier trial was carried out in men who had low selenium levels so the benefit may have come from correcting a deficiency. For vitamin E, the dose used here was higher than in previous studies - a lower dose might be more effective. Vitamin E may also be more effective at preventing cancer in those who smoke. So, it may be possible to run further trials under different conditions, to show that vitamin E and selenium prevent cancer. But on current evidence, people should not rely on supplementation to protect themselves. Research would be better focused upon finding more effective ways of warding off prostate cancer.

Source

Effect of selenium and Vitamin E on risk of prostate cancer and other cancers SM. Lippman, EA. Klein,  et al, Journal of the American Medical Association, January 7 2009, vol. 301, pp. 39--51