Association between Mediterranean diet adherence and Parkinson's disease: a systematic review and meta-analysis

•Adherence to the Mediterranean diet may reduce the risk of Parkinson's disease.•Adhering to the Mediterranean diet may help lower the risk of prodromal Parkinson's disease (pPD).•The Mediterranean diet reduces Parkinson's disease risk through anti-inflammatory effects, and improved gut microbiota and mitochondrial function. Parkinson's disease (PD) is a chronic neurodegenerative disorder, and past research suggests that adherence to the Mediterranean diet (MD) may influence the risk of PD. However, there are varying conclusions among different studies regarding the correlation between long-term adherence to the MD and the occurrence of PD. This meta-analysis aimed to investigate the association between MD adherence and PD incidence. This meta-analysis was registered on PROSPERO (CRD42024520410). We searched PubMed, Embase, Web of Science, and Cochrane databases to identify observational studies, including prospective cohorts, case-control, and cross-sectional studies, up to February 2024. Studies reported on MD adherence were included, with MD adherence categorized through a quantifying score or index. The pool odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for the highest versus the lowest categories of MD score in relation to PD risk, using random-effects models. Additionally, bias assessment, heterogeneity assessment, sensitivity analysis, and subgroup analysis were performed. A total of 12 studies were included in the meta-analysis. The overall effect size of PD risk was as follows: compared to the lowest adherence to the MD, the highest adherence to MD showed a significant negative correlation with the incidence of PD, with an overall OR of 0.75 (95% CI: 0.66, 0.84). Specifically, in studies diagnosing PD, the overall OR was 0.83 (95% CI: 0.74, 0.94), while in studies diagnosing prodromal Parkinson's disease (pPD), the overall OR was 0.67 (95%CI: 0.59, 0.76). For individuals aged