Dietary Flavonoids and Lung Cancer: A GRADE-Assessed Systematic Review and Meta-Analysis of Observational Studies

Individual observational studies examining the association between polyphenols and the risk of lung cancer have reported mixed findings. Therefore, we performed a systematic review and meta-analysis to determine the pooled effects between polyphenol intake and lung cancer risk. A systematic search was performed on PubMed, Scopus, and Web of Science databases in April 2023. Random-effect models were used to estimate odd ratios (OR) and 95% confidence intervals (95% CI). In total, 20 studies were included in the systematic review. The pooled analyses indicated that a higher intake of flavonoids (OR = 0.81; 95% CI: 0.67,0.98; p = 0.03) and isoflavone (OR = 0.82; 95% CI: 0.74,0.92; p < 0.001) were associated with lower odds of lung cancer. In addition, the ingestion of anthocyanidin (OR = 0.80; 95% CI: 0.65,0.98; p = 0.04), kaempferol (OR = 0.78; 95% CI: 0.64,0.96; p = 0.02), quercetin (OR = 0.66; 95% CI: 0.48,0.91; p = 0.01) and flavanones (OR = 0.71; 95% CI: 0.59,0.85; p < 0.001) reduced the likelihood of developing lung cancer. Overall, our findings suggest that flavonoids, isoflavones, anthocyanidin, kaempferol, quercetin, and flavanones may protect against lung cancer.