A large trial reported in 1994 that daily megadoses of the antioxidant beta-carotene increased the risk of lung cancer in male smokers by 18 percent and a 1996 trial was stopped early after researchers discovered that high-dose beta-carotene and retinol, another form of vitamin A, increased lung cancer risk by 28 percent in smokers and workers exposed to asbestos. More recently, a 2011 trial involving more than 35,500 men over 50 found that large doses of vitamin E increased the risk of prostate cancer by 17 percent.