A J-shaped association between dietary inflammatory index and COPD: A cross-sectional study from NHANES 1999 to 2018

Inflammation is a crucial factor in the development of chronic obstructive pulmonary disease (COPD). Dietary interventions that reduce inflammation are effective in managing COPD. However, little is known about the association between the DII and COPD in the general adult population in the United States. This study aimed to investigate the association between the inflammatory potential of diet and COPD in an adult population in the U.S. Data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018 were used, with COPD as the dependent variable and DII as the independent variable. Multifactor logistic regression, curve fitting, and threshold effect analyses were performed to examine this relationship. A total of 39,195 participants were included in this study, and DII was positively associated with COPD in a model adjusted for all confounders (odds ratio [OR] = 1.05; 95% confidence interval [CI], 1.02-1.09). Delineation of DII into tertiles revealed that those with the highest DII scores (T3; 2.59 to 5.48) were 23% more likely to have COPD than those in the lowest tertile (T1; -5.28 to 0.84). There was a J-shaped association between the DII and COPD (P = .003), with a turnaround point of 2.71. After the turnaround (≥2.71), a significant positive association emerged (OR = 1.268; 95% CI: 1.081-1.487). Subgroup analyses suggested no significant interactions (P values for interactions were all >.05). Our study demonstrated a J-shaped association between the DII and COPD in a nationally representative sample of U.S. adults.