Plasma antioxidants and risk of dementia in older adults

Introduction Plant-based diets rich in fruits and vegetables have been associated with lower risk of dementia, but the specific role of antioxidants, a key class of bioactive phytochemicals, has not been well ascertained. Methods We measured antioxidants in a case-cohort study nested within the Ginkgo Evaluation of Memory Study. We included 996 randomly selected participants and 521 participants who developed dementia, of which 351 were diagnosed with Alzheimer's disease (AD) during a median of 5.9 years of follow-up. We measured baseline plasma levels of retinol, alpha-, and gamma-tocopherol; zeaxanthin and lutein (combined); beta-cryptoxanthin; cis-lycopene; trans-lycopene; alpha-carotene; and trans-beta-carotene by organic phase extraction followed by chromatographic analysis and related these to neurologist-adjudicated risks of all-cause dementia and AD. Results Plasma retinol, alpha-, and gamma-tocopherol, and carotenoids were not significantly related to risk of dementia or AD. Associations were not significant upon Bonferroni correction for multiple testing and were consistent within strata of sex, age, apolipoprotein E epsilon 4 genotype, mild cognitive impairment at baseline, and intake of multivitamin, vitamin A or beta-carotene, or vitamin E supplements. Higher trans-beta-carotene tended to be related to a higher risk of dementia (adjusted hazard ratio [HR] per 1 standard deviation [SD] higher trans-beta-carotene: 1.10; 95% confidence interval [CI]: 1.00, 1.20) and alpha-carotene tended to be associated with higher risk of AD only (adjusted HR per 1 SD higher alpha-carotene: 1.15; 95% CI: 1.02, 1.29). Discussion Plasma antioxidants were not significantly associated with risk of dementia or AD among older adults. Similar studies in younger populations are required to better understand the association between plasma antioxidants and dementia risk.