History of Coffee Consumption and Risk of Alzheimer's Disease: a Meta-epidemiological Study of Population-based Cohort Studies.

Background and purpose: Four published quantitative systematic reviews showed conflicting results involving coffee consumption and the risk of Alzheimer's disease (AD). The aim of this meta-epidemiological meta-analysis (MEMA) was to evaluate the factors underlying the conflicting results and estimate the effect size and direction of the AD risk associated with coffee consumption in population-based cohort studies.

Methods: The primary subjects of MEMA were derived from 3 cohort studies selected by the related systematic reviews. Additional studies involving the primary subjects were searched using citation discovery tools. Prospective cohort studies evaluating the association between coffee consumption and AD risk were selected. A fixed effects model was applied to estimate the summary relative risk (sRR) and its 95% confidence intervals (CIs). Subgroup analysis was conducted according to the level of coffee consumption. Egger's test was used to evaluate publication bias.

Results: Four cohort studies were finally selected. A total of 36,300 participants from Finland, Sweden, Germany, and the United States of America were selected. The sRR (and its 95% CI) (I-squared value) by highest-versus-lowest method was 0.98 (0.92-1.05) (0.0%). In addition, none of the results of subgroup analyses by the level of coffee consumption showed any statistical significance.

Conclusions: This MEMA found that there was no association between coffee consumption and AD risk. Based on recent evidence suggesting that gene-environment interactions contribute to AD pathogenesis, it is necessary to conduct population-based cohort studies involving non-Caucasians.