Nonlinear association between serum vitamin D levels and asthma in U.S. adolescents ‒ Evidence from NHANES 2013-2018.

Background

while vitamin D has known immunomodulatory effects, its relationship with asthma remains inconclusive. To investigate the association between serum 25-hydroxyvitamin D [25(OH)D] levels and asthma risk in U.S. adolescents using nationally representative data, with emphasis on nonlinear dose-response relationships.

Methods

data were analyzed from 2,793 adolescents aged 12-18 years participating in NHANES 2013-2018. Asthma status was determined via self-report, and serum 25(OH)D was measured using LC-MS/MS. Multivariable logistic regression and restricted cubic spline (RCS) models were applied to evaluate linear and nonlinear associations, adjusting for relevant demographic, behavioral, and dietary covariates.

Results

no significant linear association was found between categorized vitamin D status and asthma. However, RCS analysis revealed a statistically significant U-shaped association between continuous serum 25(OH)D levels and asthma risk (p for nonlinearity = 0.019). The lowest predicted odds of asthma occurred at approximately 45.3 nmol/L, with increased risk observed at both lower and higher vitamin D levels. Key risk factors for asthma included family history (OR = 3.51), low birth weight (OR = 1.78), and reduced dietary vitamin D intake (OR per µg = 0.97).

Conclusion

a U-shaped relationship was observed between serum vitamin D levels and asthma risk in adolescents, suggesting that both deficiency and excess may be associated with higher susceptibility. These findings underscore the need for individualized, balanced vitamin D strategies and nonlinear modeling approaches in asthma research and public health policy.