Effect of antioxidant intake patterns on risks of dementia and cognitive decline.

Key summary points: Aim: This systematic review and meta-analysis aims to quantitatively investigate the relationships between the pattern of antioxidant intakes and risks of dementia and cognitive decline. Findings: For the risk of all-cause dementia, it is supplemental, not dietary, use of vitamin E or vitamin C that can significantly reduce the risk. For AD risk, dietary plus supplemental, not supplemental alone, intakes of vitamin E or vitamin C decrease markedly the risk. Furthermore, linear dose-response analyses further verified the positive effect of dietary plus supplemental intake of vitamin C on a reduced incidence of Alzheimer's dementia, with an association of every 20 mg/day increase in vitamin C and a 2% decrease in AD risk by diet plus supplement intake. Message: The findings support dietary guidelines that recommend increased intake of vitamin-C-rich foods accompanied by supplemental use of vitamin C which may be more beneficial to reduce the risk of Alzheimer-type dementia. Background: Previous studies have suggested that increased antioxidant intakes might reduce risk of cognitive disorders including Alzheimer's disease (AD). Which avenue of antioxidant intake (vitamin E/C) is more effective for decreasing risk, however, is largely unknown. Objectives: To quantitatively investigate the relationships between the pattern of antioxidant intakes and risks of dementia and cognitive decline. Methods: We searched all related prospective cohort studies reporting antioxidant intakes (diet and/or supplement) from patients with cognitive disorders. We conducted dose–response meta-analyses to assess potential linear and non-linear dose–response relationships. Summary RRs and 95% CIs were calculated using a random- or fixed-effects model. Results: 73 eligible cohort studies totaling > 28,257 participants were included in the meta-analysis; the pooled relative risks of AD were 0.75 (95% CI 0.57–0.99; I² = 59.9%) for the dietary only intake of vitamin E, 0.73 (95% CI 0.54–1.00; I² = 0%) for the dietary plus supplemental intake of vitamin E, and 0.70 (95% CI 0.51–0.95; I² = 0%) for the dietary plus supplemental intake of vitamin C. Moreover, pooled RRs of AD and vitamin C intake per 20 mg/day increase were 0.98 (95% CI 0.97–0.99) via dietary plus supplemental intake, 0.98 (95% CI 0.96–1.00) in the dietary only intake and 0.98 (95% CI 0.98–0.99) in the overall intake. There were no significant associations of all-cause dementia or cognitive impairment no dementia with the antioxidant intake. Conclusions: The risk of incident AD is significantly reduced by higher consumption of vitamin C by the intake avenue of diet plus supplement. [ABSTRACT FROM AUTHOR]