Associations between the Dietary Inflammatory Index and fractional exhaled nitric oxide among United States adults: A cross‐sectional study

BACKGROUND: Fractional exhaled nitric oxide (FeNo) is a convenient and noninvasive test that measures the concentration of nitric oxide in exhalation as a surrogate biomarker of airway inflammation. This cross-sectional study aimed to determine the associations between Dietary Inflammatory Index (DII) and FeNo in US adults. METHODS: Adults participating in the 2007-2012 cycles of the US National Health and Nutrition Examination Survey with complete information and available measurement data of DII and FeNo were included. Associations between DII and FeNo were assessed using univariable and multivariable logistic regression models, restricted cubic spline analysis, stratified analysis, and sensitivity analysis. RESULTS: A total of 7677 participants (mean age 45.68 years, 53.03% men) with a mean DII of 1.28 and FeNo of 17.33 ppb were included. The multivariable-adjusted linear regression analysis showed that a one-unit increase in DII was associated with a 0.283-ppb reduction in FeNo level. The beta and 95% CI for the second, third, and fourth DII quartile groups were -1.19 (-2.04 to -0.35), -1.07 (-2.26 to 0.12), and -1.60 (-2.85 to -0.36), respectively (P for trend = 0.04), with the lowest quartile group as the reference. The restricted cubic spline curve showed an inversely linear relationship between DII and FeNo. The study result is robust and did not appear to be affected by the participant's age, sex, race, body mass index, physical activity, diabetes status, or white blood cell or eosinophil counts. CONCLUSION: A proinflammatory diet, as indicated by a higher DII, is cross-sectionally associated with lower FeNo levels in US adults.