The Beta-Carotene and Retinol Efficacy Trial (CARET), 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 heart disease. The study was stopped early because it showed that beta-carotene/vitamin A takers 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. Researchers also found that after the intervention was stopped relative risk of cardiovascular disease mortality dropped and there was no difference in risk between the two groups. Finally, they found that women were more affected by the supplements with a larger relative risk of cardiovascular disease mortality (1.44 versus 0.93; P = .03), and all-cause mortality (1.37 versus 0.98; P = .001) than males. (10)
According to Martini et al in the University of Minnesota Cancer Prevention Research Unit Feeding Studies, an intake of 5 mg per day of beta carotene was required to establish beta carotene levels to a plasma level of 0.37 umol/L. When food based beta carotene was consumed in the form of about 1.5 cups of carrots, and about 0.9 cups of spinach which equated to just over 42 mg of beta-carotene per day, levels increased to 0.83 umol/L. (11)
