Associations between plant-based diets and cardiovascular disease, frailty, and cognitive dysfunction in middle and old age: a systematic review and meta-analysis of cohort studies.

: Evidence suggests that plant-based diets are associated with multiple health outcomes. However, in previous pooled studies, the lack of a standardized definition of plant-based diet has led to conflicting evidence regarding its relationship with health outcomes in middle-aged and elderly people. : Searches were conducted on PubMed, Embase, Cochrane Library and Web of Science databases from inception until July 10, 2024. We included studies that examined the association between (1) the standardized healthy plant-based diet index (hPDI) and unhealthy plant-based diet index (uPDI) and (2) cardiovascular disease (CVD), cardiovascular mortality (CVD mortality), frailty, and cognitive dysfunction. Dose-response analysis was performed to assess the relationships between (1) hPDI and uPDI and (2) CVD and frailty. Statistical analyses were performed using an inverse variance random-effects model, and results are reported as risk ratio (RR) with 95% confidence interval (CI) by combining the most adjusted RR, odds ratio (OR) and hazard ratio (HR) under the rare outcome assumption. A total of 25 cohort studies were included. Higher hPDI scores were associated with lower risks of CVD (RR = 0.81, 95% CI 0.71-0.93), CVD mortality (RR = 0.83, 95% CI 0.75-0.90), coronary heart disease (CHD) (RR = 0.79, 95% CI 0.70-0.88), stroke (RR = 0.91, 95% CI 0.86-0.96), ischemic stroke (RR = 0.86, 95% CI 0.79-0.94), cognitive dysfunction (RR = 0.75, 95% CI 0.66-0.84) and frailty (RR = 0.72, 95% CI 0.60-0.86). By contrast, higher uPDI scores were associated with increased risks of CVD (RR = 1.16, 95% CI 1.09-1.24), CVD mortality (RR = 1.14, 95% CI 1.05-1.23), frailty (RR = 1.52, 95% CI 1.10-2.08) and cognitive dysfunction (RR = 1.24, 95% CI 1.11-1.38). Dose-response analyses showed that increasing adherence to hPDI was associated with reduced risks of CVD and frailty, whereas increasing intake of hPDI was linked to increased risk of CVD and frailty. : Our study suggests that adherence to hPDI is associated with favourable health outcomes in middle-aged and elderly people, except for hemorrhagic stroke. These findings highlight the potential benefits of hPDI for promoting healthy ageing.