BACKGROUND: Some studies have suggested that beta-carotene supplementation may increase the risk of lung cancer, particularly among smokers or former smokers. Beta-carotene, a provitamin A, is available in multivitamins. In the current study, the authors investigated the risk of lung cancer associated with beta-carotene in smokers or former smokers and surveyed the beta-carotene content in national brand multivitamins. METHODS: The authors systemically reviewed the published literature using a search of the MEDLINE database and performed a meta-analysis of large randomized trials that reported on the effect of beta-carotene supplementation on the incidence of lung cancer among smokers or former smokers. A sample of multivitamins was evaluated for their beta-carotene content and the suggested daily dosage. RESULTS: Four studies contributing 109,394 subjects were available for analysis. The average daily beta-carotene dosage in these trials ranged from 20 to 30 mg daily. Among current smokers, beta-carotene supplementation was found to be significantly associated with an increased risk of lung cancer (odds ratio [OR], 1.24; 95% confidence interval [95% CI], 1.10-1.39). Among former smokers, there was no significant increase noted (OR, 1.10; 95% CI, 0.84-1.45). In a sample of 47 common multivitamins, beta-carotene was present in 70% of the identified formulas. The median dosage of beta-carotene was 0.3 mg (range, 0-17.2 mg) daily. The beta-carotene content was found to be significantly higher among multivitamins sold to improve visual health than among other multivitamins, with a median daily dosage of 3 mg (range, 0-24 mg). CONCLUSIONS: High-dose beta-carotene supplementation appears to increase the risk of lung cancer among current smokers. Although beta-carotene was prevalent in multivitamins, high-dose beta-carotene was observed among multivitamin formulas sold to promote visual health. (Copyright) 2008 American Cancer Society.