WASHINGTON : Men should not take high doses of vitamin E or selenium supplements because they have no health benefits and increase the risk of prostate cancer by up to a fifth, scientists have claimed. Vitamin E, naturally found in nuts, spinach and broccoli, is taken to boost the body’s immune system and the mineral selenium, found in fish and meat, is taken to ward off heart disease. But US researchers claim large doses of both can increase the risk of prostate cancer by 17 per cent. This can rise to as much as 91 per cent if a man already has high levels of selenium before taking supplements.