Overdosing on the mineral selenium by taking supplements raised the chances of developing high-grade cancer by 91%, scientists found. Vitamin E pills also raised the risk of aggressive cancer, more than doubling it for men lacking selenium.
The researchers believe selenium can turn toxic in the body at excessively high levels. At the same time, the mineral appeared to protect against the harmful effects of too much vitamin E.
The US study was a follow-up of Select, the Selenium and Vitamin E Cancer Prevention Trial, which originally recruited more than 35,000 men to see if the supplements could help prevent prostate cancer.
Researchers stopped the trial three years early in 2008 after there were hints that instead of protecting men, vitamin E was putting them at greater risk.
Dr Alan Kristal, from Seattle's Fred Hutchinson Cancer Research Centre, said: "Men using these supplements should stop, period. Neither selenium nor vitamin E supplementation confers any known benefits, only risks."