Plant-based diet and risk of cognitive decline among older adults: a community-based prospective cohort study

Background: Diet serves as a modifiable risk factor for cognitive decline, yet evidence on plant-based diets and cognitive ageing remains limited. We examined the association between plant-based diets and cognitive decline.Methods: A total of 6,721 participants from the Chinese Longitudinal Healthy Longevity Survey (CLHLS) were included. Dietary intake was assessed using a simplified food frequency questionnaire to derive the Plant-based Diet Index (PDI), healthy PDI (hPDI), and unhealthy PDI (uPDI). Global cognitive function and six specific domains were assessed using the Mini-Mental State Examination (MMSE). Z-scores were calculated using baseline mean and standard deviation. Linear mixed-effects and Cox models were used to evaluate the associations between plant-based diets and cognitive decline.Findings: Over 5·57 years of follow-up, 1,580 participants developed cognitive impairment. Participants in the highest tertiles of PDI and hPDI showed a 32·04% and 31·43% slower rate of cognitive decline (β = -0·071, 95% CI: -0·079 to -0·062; β = -0·071, 95% CI: -0·080 to -0·063), while those in the highest uPDI tertile showed a 21·79% faster decline rate (β = -0·095, 95% CI: -0·104 to -0·087). The highest tertile of hPDI was associated with a 6·6% reduction in cognitive impairment risk (HR = 0·934, 95% CI: 0·828–1·055), whereas high uPDI increased risk (HR = 1·263, 95% CI: 1·116–1·430). Similar associations were observed in the competing risk model.Interpretation: Higher adherence to the hPDI was associated with a slower rate of cognitive decline and a reduced risk of incident cognitive impairment, whereas greater adherence to the uPDI corresponded to accelerated cognitive decline.