Serum Retinol Levels and Risk of Asthma: Evidence From the NHANES and Mendelian Randomization

Given the ongoing controversy regarding the relationship between serum retinol levels and asthma, this study aims to clarify their association in adults through an integrated analysis of National Health and Nutrition Examination Survey (NHANES) data and a two‐sample Mendelian randomization (MR) study. Cross‐sectional analysis of 10,136 participants from NHANES (1999–2006 and 2017–2018), using weighted multivariate logistic regression, revealed that serum retinol levels were negatively associated with adult asthma (OR = 0.89, 95% CI: 0.74–0.99, p = 0.044). Subsequent two‐sample MR analysis with genome‐wide association study (GWAS) statistics (serum retinol: ukb‐b‐17406, N = 62,991; asthma: ebi‐a‐GCST006862, N = 127,669) employed Inverse Variance Weighted method (instrument selection threshold: p < 1×10 −5 , F ‐statistic > 10), confirming a causal effect in which genetically predicted higher retinol levels reduced asthma risk (OR = 0.62, 95% CI: 0.41–0.93, p = 0.021). Sensitivity analyses (MR‐Egger/MR‐PRESSO) detected no significant pleiotropy ( p > 0.05 in both tests). This study suggests a potential causal link between higher serum retinol levels and a reduced prevalence of adult asthma.