Associations of the inflammatory diet index and smoking status with the risk of chronic obstructive pulmonary disease and lung cancer.

It remains unknown whether a low-inflammatory diet could modify the chronic obstructive pulmonary disease (COPD) and lung cancer risk related to smoking. To investigate the association between a low-inflammatory diet, smoking status, and the risk of COPD and lung cancer. A total of 171 050 COPD-free and lung cancer-free (mean age: 55.80) individuals were included in this study. COPD and lung cancer were defined as hospital admission. An inflammatory diet index (IDI) was developed based on C-reactive protein levels and was a weighted sum of 34 food groups. Participants were grouped into tertiles corresponding to IDI scores (lowest, middle, and highest). Over 2 091 071 person-years of follow-up, a total of 4007 individuals developed COPD (person-years: 2 075 579), and 1049 developed lung cancer. In comparison with the highest tertile of the IDI score, hazard ratios (HRs) and 95% confidence intervals (CIs) of COPD and lung cancer related to a low-inflammatory diet were 0.66 (0.61, 0.72) and 0.76 (0.65, 0.89), respectively. A low-inflammatory diet may prolong COPD onset by 1.88 (1.50, 2.27) years and lung cancer onset by 1.05 (0.45, 1.65) years. In joint effect analyses, participants with the lowest/middle IDI score and smoking had a significant 37% decrease in COPD risk and a 35% decrease in lung cancer risk compared to the participants with the highest IDI score and smoking. Replacing each standard deviation unit (≈1080.426 g day) of pro-inflammatory foods with anti-inflammatory foods was associated with a 30% lower COPD risk. Our findings suggest that a low-inflammatory diet may significantly mitigate the risk of smoking on COPD development, and delay the COPD onset by about 2 years. However, a low-inflammatory diet is associated with a reduced risk of lung cancer among only smokers. Substituting equal intake of pro-inflammatory foods with anti-inflammatory foods is related to a decreased risk of COPD, but not lung cancer.