Fig 3. The relationship between dietary niacin intake and COPD stratified using different characteristics.

Except for the stratification component itself, each stratification factor was adjusted for all other variables (sex, age, race/ethnicity, family income, physical activity, smoking status, education level, marital status, body mass index, Serum cotinine, total energy, hypertension, high cholesterol, diabetes, coronary heart disease, stroke, cancer.).Abbreviations: COPD, chronic obstructive pulmonary disease; OR, odds ratio; 95% CI, 95% confidence interval.