Unfortunately, results in humans have been more mixed. In one study, male smokers were given supplements of beta-carotene, a form of vitamin A, and an antioxidant. Surprisingly, their incidence of lung cancer was slightly higher than in those smokers taking placebo. In the Women's Health Study, taking supplements of beta-carotene neither prevented nor promoted cancer in smokers. Other studies suggest that taking Vitamin C and E supplements is associated with decreased rates of cancer, as well.
Some researchers speculate that caloric reduction works in part by inducing more DNA repair.