Prevents cancer: After five years of tantalizing evidence that selenium might prevent cancer, a groundbreaking new study seems to confirm it. Physician Larry Clark, of the University of Arizona, found that a modest dose of a selenium supplement reduced overall cancer incidence by 42 percent. Further, taking selenium slashed cancer death rates in half. Clark's randomized double-blind study (the "gold standard" in medical research) followed 1,312 older people with common skin cancer an average of seven years. Half took 200 micrograms of selenium daily; the others took a placebo (inactive pill). Clark had expected selenium to block the recurrence of skin cancers. It did not. But he began to notice a striking drop in other cancers. His final analysis shows that taking selenium slashed the occurrence of prostate cancer by 69 percent; colorectal cancer, 64 percent; and lung cancer, 39 percent. The finding is unprecedented - the first real scientific proof of any nutrient's power to prevent cancer in humans.