A longitudinal cohort study demonstrating the beneficial effect of moderate consumption of green tea and coffee on the prevention of dementia: The JPHC Saku Mental Health Study

Background: While the preventive effects of green tea and coffee on cognitive decline have been demonstrated, their long-term effects on cognition remain unclear. Objective: This study aims to investigate the effect of green tea and coffee consumption in middle age on the prevention of dementia. Methods: This population-based cohort study included 1155 participants (aged 44–66 in 1995). Participants’ consumption of green tea and coffee was assessed using questionnaires in 1995 and 2000. Their cognitive levels were neuropsychologically evaluated in 2025–2015. Logistic regression analyses were conducted with significant cognitive decline (defined as multi-domain cognitive decline and more severe conditions) as the dependent variable. Stratified analyses were also conducted by sex and age. Results: Individuals who consumed 2–3 cups of green tea daily had a significantly reduced risk of cognitive decline (OR = 0.56, 95%CI: 0.35–0.91) after adjusting potential confounders. However, this effect was not significant with consumption of 4 or more cups. This protective effect was particularly observed in males (OR = 0.38, 95%CI: 0.19–0.76). A significant risk reduction was also observed in individuals consuming one or more cups of coffee daily (OR = 0.54, 95%CI: 0.34–0.84) in the older subjects (median age [53 years old] and older in 1995) in the same fully adjusted model, but not in the entire sample. Conclusions: Our findings suggest that moderate green tea consumption in midlife may have a beneficial effect on preventing dementia, particularly in males. The effects of coffee consumption may be more advantageous for older individuals.