Association Between Metabolic Syndrome and the Risk of Lung Cancer: A Meta-Analysis

Previous studies showed conflicting results regarding the association between metabolic syndrome (MetS) and risk of lung cancer. We performed a systemic review and meta-analysis to determine the relationship between MetS and lung cancer incidence and mortality in adults. Longitudinal follow-up studies were identified by search of Medline, Embase, Cochrane Library, and Web of Science. By incorporating potential heterogeneity into the model, a randomized-effects model was selected to pool the results. Fourteen observational studies were included. Pooled results showed that MetS was associated with a higher risk of lung cancer incidence [risk ratio (RR): 1.15, 95% confidence interval (CI): 1.05 to 1.26, p=0.002; I²=89%). Subgroup analysis suggested that the association was not significantly affected by study country, design, sex of the participants, adjustment of smoking, or different study quality scores (p for subgroup difference all>0.05). The association was predominantly contributed by studies with MetS defined by the National Cholesterol Education Program Adult Treatment Panel-III rather than those with MetS defined by the International Diabetes Foundation criteria, and the association seemed to be stronger in studies with follow-up within 6 years than those over 6 years (p for subgroup difference=0.03 and 0.04, respectively). In addition, pooled results also showed that MetS was associated with a higher risk of lung cancer mortality (RR: 1.46, 95% CI: 1.19 to 1.79, p <0.001; I²=0%). In conclusion, in adult population, MetS may be a risk factor of lung cancer incidence and mortality.