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 = 6642), Framingham Heart Study Offspring cohort (FOS; N = 3045), and Whitehall II study (WHII; N = 8219). 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 scores in PDI and hPDI were 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). Main contributors to lower risk were higher intake of vegetables, nuts, tea or coffee, and legumes. Conversely, higher uPDI was associated with higher dementia risk (highest vs. lowest tertile: pooled HR = 1.42, 1.19–1.70, p for trend < 0.001). In the meta-analysis, individuals in the highest hPDI tertile had 21% lower dementia risk, and those in the highest uPDI tertile had 24% higher risk.

The healthful plant-based diet was associated with lower risk of dementia, whereas the unhealthful plant-based diet was linked to higher risk. These findings support recommendations to adopt diets rich in healthy plant foods for dementia prevention.