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

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.