Plant-based diets are increasingly advocated for their health benefits, yet their associations with dementia risk remains inconclusive. We evaluated the associations between plant-based dietary patterns and dementia risk across three prospective cohorts and a meta-analysis.

Cohort analyses included the Health and Retirement Study (HRS; N=6,642), Framingham Heart Study Offspring cohort (FOS; N=3,045), and Whitehall II study (WHII; N=8,219). Participants were aged ≥45 years and free of dementia at baseline. The overall plant-based diet index (PDI), healthful plant-based diet index (hPDI) and unhealthful plant-based diet index (uPDI) were calculated from validated food frequency questionnaires. Further, a meta-analysis was conducted incorporating data from 5 cohort studies (N=207,981).

In the cohort analyses, 891 incident dementia cases were identified over 166,762 person-years. In multivariable-adjusted Cox proportional hazard models, higher adherence to PDI and hPDI was associated with lower risk of dementia (highest vs. lowest tertile: pooled HR for PDI=0.70, 95% CI, 0.53-0.92, p for trend < 0.001; pooled HR for hPDI=0.71, 0.48-1.06, p for trend=0.03). Conversely, uPDI was associated with higher dementia risk (pooled HR _{Tertile3 vs. Tertile1} =1.42, 95% CI, 1.19-1.70, p for trend < 0.001). Main protective contributors were vegetables, nuts, tea or coffee, and legumes. In the meta-analysis, individuals in the highest hPDI tertile had 21% lower dementia risk, while the highest uPDI tertile had 24% higher risk.

The healthful plant-based diet is associated with lower risk of dementia. These findings support recommendations to adopt diets rich in healthy plant foods and minimizing in unhealthy plant foods and animal products for dementia prevention.