The Beta-Carotene and Retinol Efficacy Trial (CARET):
The CARET trial showed that among 18,314 men and women who smoked heavily or were exposed to asbestos, daily intake of 30 mg (100,000 IU) of beta-carotene and 25,000 IU vitamin A failed to decrease the risk of cancer. The study was stopped early because it showed that beta-carotene/vitamin A users who were heavy smokers, ex-smokers or asbestos workers were showing a 28% increased risk of lung cancer in smokers (versus placebo) and a 17% more likely chance of dying, mostly of lung cancer or heart disease. Results of a 6-year follow-up of study participants showed that compared to the placebo or no intervention group, participants who had taken the intervention had a 12% and 8% increase in relative risk of lung cancer and all-cause mortality among the intervention group, respectively. They found that women were more affected by the supplements with a larger relative risk of lung cancer mortality (1.33 versus 1.14; P = .36), and all-cause mortality (1.37 versus 0.98; P = .001) than males. (3)