The vitamin instead appeared to raise risk of heart failure in some cases, shows the study in today's issue of the Journal of the American Medical Association (vol 293, pp1338-1347).
Previous data suggests that vitamin E supplementation may help prevent cancer and cardiovascular events but clinical trials have not confirmed this, possibly due to their relatively short duration. The researchers sought to find out whether a benefit could come from long-term supplement use.
Their findings could do further short-term damage to vitamin E trade, not long after a meta-analysis published on the Annals of Internal Medicine website in November also raised safety questions over the vitamin. It concluded that data from 19 studies demonstrated an increased risk of all-cause mortality from high dose (400IU) vitamin E supplements.
The team from the Population Health Research Institute and McMaster University as well as Hamilton Health Sciences Corporation in Canada followed 738 patients, aged at least 55 years old, with vascular disease or diabetes for an average of seven years. The patients were part of the extension to the Heart Outcomes Prevention Evaluation (HOPE) trial conducted from 1993 to 1999, called HOPE-TOO. This trial ran from April 1999 to May 2003.
During the researchers follow-up time, the patients took a daily dose of 400 IU natural source vitamin E or placebo.
There were no significant differences between the two groups in the primary outcomes of cancer incidence, cancer deaths and major cardiovascular events like stroke and death.
However patients in the vitamin E group had a 13 per cent higher risk of heart failure and were 21 per cent more likely to be hospitalized for heart failure.
"The potential for harm suggested by our findings strongly supports the view that vitamin E supplements should not be used in patients with vascular disease or diabetes mellitus," write the study authors.
Dr Annette Dickinson, president of the US-based trade association the Council for Responsible Nutrition, noted that since these results have not been seen in other studies, the risks to heart health could be a chance effect.
"There is certainly no evidence that these kinds of effects would occur in healthy populations," she added, pointing out that the findings applied only to an older group of patients, with an average age of over 70 and a history of heart disease, stroke or diabetes.
"This is certainly not the final word on vitamin E and should not obscure the fact that for millions of healthy people vitamin E has many long-term benefits, including protecting against oxidative damage in body cells and reducing harmful inflammation," added Dr Dickinson.
A number of clinical trials on vitamin E are ongoing, including one involving more than 34,000 men evaluating whether vitamin E and selenium can reduce the risk of prostate cancer.
The CRN has compiled information on the safety of vitamin E on its website.