Adherence to the Mediterranean diet and the risk of lung cancer: A systematic review and dose-response meta-analysis of observational studies

Context: The literature supports the protective role of the Mediterranean diet (MD) in the prevention of some types of cancer, such as colorectal and liver cancer. The link between the MD and lung cancer, however, is still unclear. Objective: The aim of this systematic review and meta-analysis was to investigate the association between the MD and risk of lung cancer. Data Sources: Electronic databases (PubMed, Scopus, Embase, and Web of Science) were searched up to May 2021. Study Selection: Case-control and cohort studies reporting the association between intake of the MD and risk of lung cancer and with accessible full texts published in English were included. Review articles, laboratory and animal studies, abstracts, letters to the editor, and studies lacking sufficient data were excluded. Data Extraction: The risk ratio (RR) was extracted from eligible studies, and meta-analysis was performed to calculate the pooled RR of the included studies. Results: Nine studies (8 cohort, 1 case-control) were included in the meta-analysis. High adherence to the MD was associated with a lower likelihood of lung cancer compared with low adherence (RR = 0.84; 95%CI, 0.77-0.91; I2 = 52%, heterogeneity P = 0.03). Dose-response analysis showed that a 2-score increment in MD adherence was associated with a 6% lower risk of lung cancer (RR = 0.94; 95%CI, 0.91-0.96; nonlinearity P = 0.97). Subgroup analyses showed a protective association between MD adherence and risk of lung cancer among former smokers (n = 3 studies) (RR = 0.81; 95%CI, 0.74-0.89), but no significant association was observed for never smokers (n = 3 studies) (RR = 0.78; 95%CI, 0.29-2.07) or current smokers (n = 3 studies) (RR = 0.82; 95%CI, 0.58-1.16). In addition, an inverse association between the MD and lung cancer was observed in both males (RR = 0.84; 95%CI, 0.74-0.96) and females (RR = 0.87; 95%CI, 0.77-0.98). Conclusions: High adherence to the MD is associated with a lower risk of lung cancer, especially in former smokers. Systematic Review Registration: PROSPERO registration no. CRD42019146460.