Adherence to the Mediterranean Diet and all-cause mortality: a systematic review and meta-analysis within the Italian National Guidelines “La Dieta Mediterranea”

Background: The Mediterranean diet (MD) is a dietary pattern associated with reduced chronic disease risk and increased longevity. This systematic review and meta-analysis aimed to evaluate the association between adherence to the MD and all-cause mortality in adult populations. Methods: A comprehensive literature search was conducted in PubMed/MEDLINE, Cochrane Library, Embase, and Scopus (search date: February 28, 2024) without date restrictions. Prospective and retrospective cohort studies examining the association between MD adherence (measured by any validated score) and all-cause mortality were included. Study selection and data extraction were performed independently by pairs of reviewers using Covidence. Risk of bias was assessed using the Newcastle–Ottawa Scale. Random-effects meta-analysis was conducted, estimating pooled relative risks (RRs) per 1-point increment in MD adherence score. Heterogeneity was assessed using the I² statistic, and publication bias was evaluated by funnel plot. Certainty of evidence was graded using the NUTRIGRADE approach. Results: Out of 5,229 screened records, 54 cohort studies were included, comprising 1,833,267 participants and 346,034 deaths. Studies spanned diverse populations and geographic regions, with follow-up ranging from 2 to 60 years. The pooled RR for all-cause mortality per 1-point increase in MD adherence was 0.96 (95% CI: 0.95–0.97), indicating a statistically significant protective effect. The overall certainty of evidence was rated as moderate. Conclusions: Higher adherence to the MD is associated with a reduced risk of all-cause mortality. These findings support public health strategies promoting the MD as a sustainable dietary model for longevity.