Grodstein F, et al. A randomized trial of beta carotene supplementation and cognitive function in men: the Physicians' Health Study II. Arch Intern Med. Nov 12 2007;167(20):2184-2190.
The effects of short-term or long-term beta-carotene supplementation (50 mg every other day) on cognitive function were determined in participants from the Physicians' Health Study II. Participants (men >65 years) were analyzed for general cognition, verbal memory, and category fluency. Although participants receiving beta-carotene supplementation for a mean of 1 year did not show any improvements in cognitive function, those in the long-term group (mean duration of 18 years) had increased cognitive performance compared to the placebo-control group. Due to the possible health risks associated with beta-carotene supplementation, further studies are required to determine the risk-to-benefit ratio of beta-carotene supplementation.
Arnlov J, et al. Serum and dietary beta-carotene and alpha-tocopherol and incidence of type 2 diabetes mellitus in a community-based study of Swedish men: report from the Uppsala Longitudinal Study of Adult Men (ULSAM) study. Diabetologia. Nov 5 2008.
To determine if serum levels or dietary intake of beta-carotene influence the incidence of type 2 diabetes, 846 non-diabetic men (50 years of age) were followed up to 27 years in this longitudinal study. Participants with the highest serum levels of beta-carotene had reduced risk of developing type 2 diabetes. Conversely, impaired insulin sensitivity was associated with low serum beta-carotene. Further studies are required to determine if beta-carotene is associated with the incidence of type 2 diabetes in women.
Satia JA, Littman A, Slatore CG, Galanko JA, White E. Long-term use of beta-carotene, retinol, lycopene, and lutein supplements and lung cancer risk: results from the VITamins And Lifestyle (VITAL) study. Am J Epidemiol. 2009 Apr 1;169(7):815-28.
This study was conducted to determine associations of supplemental beta-carotene, retinol, vitamin A, lutein, and lycopene with lung cancer risk in 77,126 subjects, aged 50-76 years, in the VITamins And Lifestyle (VITAL) cohort Study in Washington State between 2000 and 2002. Participants completed a 24-page questionnaire about supplement use including duration, frequency, and dose during the previous 10 years from multivitamins and individual supplements/mixtures. Five hundred and twenty-one cases of incident lung cancers were identified. Longer duration of beta-carotene, retinol and lutein supplements was associated wtih statistically significant higher risk of total lung cancer. Gender or smoking status did not affect the risk.
The authors concluded that long-term supplementation with beta-carotene, retinol, and lutein should not be recommended for preventing lung cancer, particularly among smokers.