Adherence to Mediterranean diet and risk of cancer: an updated systematic review and meta‐analysis of observational studies

The aim of the present systematic review and meta‐analysis of observational studies was to gain further insight into the effects of adherence to Mediterranean Diet (MD) on overall cancer mortality, incidence of different types of cancer, and cancer mortality risk in cancer survivors. Literature search was performed using the electronic databases PubMed, and EMBASE until 2 July 2015. We included either cohort (for specific tumors only incidence cases were used) or case–control studies. Study specific risk ratios, hazard ratios, and odds ratios (RR/HR/OR) were pooled using a random effect model. The updated review process showed 23 observational studies that were not included in the previous meta‐analysis (total number of studies evaluated: 56 observational studies). An overall population of 1,784,404 subjects was included in the present update. The highest adherence score to an MD was significantly associated with a lower risk of all‐cause cancer mortality (RR: 0.87, 95% CI 0.81–0.93, I (2) = 84%), colorectal cancer (RR: 0.83, 95% CI 0.76–0.89, I (2) = 56%), breast cancer (RR: 0.93, 95% CI 0.87–0.99, I (2)=15%), gastric cancer (RR: 0.73, 95% CI 0.55–0.97, I (2) = 66%), prostate cancer (RR: 0.96, 95% CI 0.92–1.00, I (2) = 0%), liver cancer (RR: 0.58, 95% CI 0.46–0.73, I (2) = 0%), head and neck cancer (RR: 0.40, 95% CI 0.24–0.66, I (2) = 90%), pancreatic cancer (RR: 0.48, 95% CI 0.35–0.66), and respiratory cancer (RR: 0.10, 95% CI 0.01–0.70). No significant association could be observed for esophageal/ovarian/endometrial/and bladder cancer, respectively. Among cancer survivors, the association between the adherence to the highest MD category and risk of cancer mortality, and cancer recurrence was not statistically significant. The updated meta‐analyses confirm a prominent and consistent inverse association provided by adherence to an MD in relation to cancer mortality and risk of several cancer types.