Serum total bilirubin and childhood asthma: Results of the NHANES 2007–2018 and Mendelian randomization study

Total bilirubin possesses antioxidant and immunomodulatory properties, and its role in childhood asthma is a topic of ongoing debate. We employed both a cross-sectional study and Mendelian randomization (MR) analysis to explore the link between serum total bilirubin and childhood asthma. In the cross-sectional study from the National Health and Nutrition Examination Survey 2007 to 2018, weighted logistic regression models were utilized to investigate the association between serum total bilirubin and childhood asthma. We also used restricted cubic splines to explore the dose-response relationship between the 2. The inverse-variance weighted method was used as the main method of MR analysis to explore the causal effect of exposure on outcomes. A total of 3238 participants were included in the cross-sectional study. Weighted logistic regression analysis encompassing all participants revealed no significant association between total bilirubin levels and the risk of childhood asthma ( P  > .05). The same results were obtained after categorizing participants into tertiles based on total bilirubin levels. The restricted cubic splines curve revealed an S-shaped relationship between total bilirubin levels and childhood asthma. MR analysis reveals no causal association between serum total bilirubin and childhood asthma (odds ratio [OR] = 0.974, P  = .752), peak expiratory flow (OR = 1.002, P  = .831), and forced expiratory volume in 1-second (OR = 1.005, P  = .554). Our study did not support a causal relationship between serum total bilirubin and childhood asthma. Further studies with a larger number of cases are crucial to validate our findings.