A meta-analysis of peripheral tocopherol levels in age-related cognitive decline and Alzheimer's disease

Abstract

Objectives: Findings from observational studies and clinical trials on the associations between vitamin E and dementia remain controversial. Here we conducted a meta-analysis to determine the difference in blood tocopherols levels between patients with Alzheimer's disease (AD) or age-related poor cognitive function and healthy controls.Methods: Standardised mean difference (SMD) and 95% confidence intervals (CIs) were calculated and entered into a random effects model. Study quality, heterogeneity and publication bias were also investigated.Results: Thirty-one articles were included in the meta-analysis, which included analyses for α-, β-, γ- and δ-tocopherols. These results indicated that individuals with AD or age-related cognitive deficits and mild cognitive impairment (MCI) had lower circulatory concentrations of α-tocophenol compared with healthy controls (AD: SMD = -0.97, 95% confidence interval [CI] = -1.27 to -0.68, Z = 6.45, P < 0.00001; age-related cognitive deficits and MCI: SMD = -0.72, 95% CI = -1.12 to -0.32, Z = -3., P < 0.0005). Levels of β-, γ- and δ-tocophenols did not significantly differ between groups of AD and age-related cognitive deficits compared to controls.Discussion: These results suggest that lower α-tocopherol levels have a strong association with AD and MCI supporting evidence for the role of diet and vitamin E in AD risk and age-related cognitive decline.

Keywords: Alzheimer's disease; MCI; Vitamin E; diet; meta-analysis; α-tocopherol; γ-tocopherol.