Associations between dietary fat-soluble vitamins and pulmonary function and airway inflammation: A cross-sectional study.

Pulmonary function and airway inflammation are key indicators of respiratory health. Dietary factors, particularly fat-soluble vitamins, may be related to these outcomes, yet their associations in general populations remain inadequately characterized. We analyzed data from the National Health and Nutrition Examination Survey 2007 to 2012, including 9328 adults. Fat-soluble vitamin intake (A, D, E, K) was assessed via 24-hour dietary recalls. Spirometry measures (forced vital capacity, forced expiratory volume in the first second [FEV1], forced expiratory flow between 25% and 75% of vital capacity) and fractional exhaled nitric oxide (FeNO) were used to assess pulmonary function and airway inflammation, respectively. Multivariable linear regression and generalized additive models were employed to evaluate associations, with adjustment for sociodemographic, lifestyle, and clinical factors. In fully adjusted models, vitamins A and D were positively associated with forced vital capacity (β = 0.04 mL and 3.72 mL per µg/day, respectively). Vitamins A and K were positively associated with FeNO (β = 1.1 ppb and 3.3 ppb per unit increase, respectively). Exploratory analyses using generalized additive models identified nonlinear inverted U-shaped relationships for vitamins A and D with FEV1, with threshold points at 958 µg/day and 11.95 µg/day. Below these thresholds, each unit increase in vitamin A and vitamin D intake was associated with an increase in FEV1 of 0.07 mL and 4.15 mL, respectively. These threshold values are exploratory and require validation in future studies. Subgroup analyses indicated significant interactions with body mass index, particularly among overweight individuals. Dietary intake of vitamins A and D is positively associated with lung function, while vitamins A and K are positively associated with FeNO in a cross-sectional analysis. These findings highlight the complex associations between fat-soluble vitamins and respiratory health indicators, providing population-level observational evidence for future research on nutritional factors and lung health. Exploratory analyses suggest inverted U-shaped relationships between vitamins A and D and FEV1, but these findings are hypothesis-generating and require validation. No causal or preventive implications can be drawn from this cross-sectional analysis.