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.