Effect of Daily Coffee Consumption on the Risk of Alzheimer's Disease: A Systematic Review and Meta-Analysis.

Alzheimer's disease (AD) is a highly prevalent neurodegenerative disorder that affects millions of individuals globally. The identification of the lifestyle factors that potentially help prevent or postpone disease onset is of interest to the researchers. Although the study results are inconsistent, one such factor that has been extensively studied is coffee consumption. Therefore, this meta-analysis primarily aimed to investigate the effects of coffee consumption on the risk of AD. Pubmed, Embase, and Web of Science (Only Writing Web of Science is Fine) databases were searched for relevant studies with the keywords in various combinations, including "coffee", "caffeine", and "Alzheimer's disease". This meta-analysis included 11 studies. The relative risk (RR) with 95% confidence intervals (CI) was calculated to estimate the effect size. The study used the restricted maximum-likelihood method for a generic-inverse-variance analysis with random-effect (when heterogeneity, I2 > 50%) or fixed-effect (when heterogeneity, I2 < 50%) modeling. The study protocol has been registered at International Prospective Register of Systematic Reviews (CRD42023429016). Individuals that regularly consumed 1-2 cups and 2-4 cups coffee/day demonstrated a significantly lower risk of developing AD (1-2 cups/day: RR = 0.68, 95% CI = 0.54 to 0.83, I2 = 50.99%, p = 0.00 [the software used for analysis, shows the results of p value like this (0.00), I prefer not to change this as this is also fine]; 2-4 cups/day: RR = 0.79, 95% CI = 0.56 to 1.02, I2 = 71.79%, p = 0.00). However, individuals who consumed > 4 cups/day demonstrated an increased risk of developing AD (RR = 1.04, 95% CI = 0.91 to 1.17, I2 = 0.00%, p = 0.00). This meta-analysis indicates that limited (1-4 cups/day) daily coffee consumption reduces the risk of AD, whereas excessive consumption (> 4 cups/day) might increase the risk.