Plant-Based Dietary Patterns and Risk of Alzheimer Disease and Related Dementias in the Multiethnic Cohort Study.

BACKGROUND AND OBJECTIVES: Plant-based diets have been linked to slower cognitive decline, but data on long-term dietary changes and from diverse populations are limited. The primary aim of this study was to examine plant-based dietary patterns and their change over time in relation to Alzheimer disease and related dementias (ADRDs). METHODS: This prospective longitudinal analysis of the Multiethnic Cohort Study, based in Hawaii and California (primarily Los Angeles County), included data on African American, Japanese American, Latino, Native Hawaiian, and White participants who completed food frequency questionnaires at baseline (1993-1996; age 45-75 years) and at 10-year follow-up (2003-2008) and whose Medicare claims were linked to identify incident ADRDs. A priori indices for the overall plant-based diet index (PDI), the healthful plant-based diet index (hPDI), and the unhealthful plant-based diet index (uPDI) were analyzed in Cox regression models for ADRD. RESULTS: The analysis included 92,849 participants (mean age 59.2 years, 55.1% female, 21,478 with ADRDs) for the baseline diet and 45,065 participants (8,360 with ADRDs) for the 10-year dietary change. For the baseline diet, comparing the highest vs lowest quintile, PDI and hPDI were associated with 12% (hazard ratio [HR] 0.88; 95% CI 0.85-0.92) and 7% (HR 0.93; 95% CI 0.89-0.97) lower risks of ADRD, respectively, whereas uPDI was related to a 6% higher risk (HR 1.06; 95% CI 1.01-1.10). For the dietary change over time, the strongest association with ADRD was observed for uPDI rather than for PDI or hPDI. Compared with those with a stable score (<0.5 SD change), participants with a large increase in uPDI (≥1 SD) showed a 25% higher risk (HR 1.25; 95% CI 1.15-1.36) and those with a large decrease in uPDI showed an 11% lower risk (HR 0.89; 95% CI 0.84-0.94). The associations between the plant-based diet indices and ADRD were generally similar by age group (<60 vs ≥60 years at baseline), race and ethnicity, or DISCUSSION: These findings suggest that adopting plant-based diets, specifically refraining from low-quality plant-based diets, even at an older age, is associated with a lower risk of ADRDs.