The effectiveness of the Mediterranean Diet for primary and secondary prevention of cardiovascular disease: An umbrella review

Aims: This study aimed to review meta-analyses of randomised controlled trials that evaluated the effectiveness of the Mediterranean Diet for the primary and secondary prevention of cardiovascular disease. Methods: Five databases (Medline, Embase, Cochrane, CINAHL and ProQuest) were searched from inception to November 2022. Inclusion criteria were: (i) systematic review of randomised controlled studies with metanalysis; (ii) adults >= 18 years from the general population with (secondary prevention) and without (primary prevention) established cardiovascular disease; (iii) Mediterranean Diet compared with another dietary intervention or usual care. Review selection and quality assessment using AMSTAR-2 were completed in duplicate. GRADE was extracted from each review, and results were synthesised narratively. Results: Eighteen meta-analyses of 238 randomised controlled trials were included, with an 8% overlap of primary studies. Compared to usual care, the Mediterranean Diet was associated with reduced cardiovascular disease mortality (n = 4 reviews, GRADE low certainty; risk ratio range: 0.35 [95% confidence interval: 0.15-0.82] to 0.90 [95% confidence interval: 0.72-1.11]). Non-fatal myocardial infarctions were reduced (n = 4 reviews, risk ratio range: 0.47 [95% confidence interval: 0.28-0.79] to 0.60 [95% confidence interval: 0.44-0.82]) when compared with another active intervention. The methodological quality of most reviews (n = 16/18; 84%) was low or critically low and strength of evidence was generally weak. Conclusions: This review showed that the Mediterranean Diet can reduce fatal cardiovascular disease outcome risk by 10%-67% and non-fatal cardiovascular disease outcome risk by 21%-70%. This preventive effect was more significant in studies that included populations with established cardiovascular disease. Better quality reviews are needed.