Association between arthritis and asthma: An observational analysis of NHANES and a Mendelian randomization study

Observational studies have linked arthritis and asthma, but establishing causality is challenging due to confounding. We analyzed 30,001 adults from the National Health and Nutrition Examination Survey (2003–2018) using survey-weighted logistic regression to assess observational associations. To infer causality, we conducted a two-sample Mendelian randomization analysis using publicly available genetic data. In the observational analysis, arthritis was significantly associated with a higher risk of asthma (adjusted odds ratio = 1.96, 95% confidence interval = 1.75–2.19), with similar findings for rheumatoid arthritis (RA) and osteoarthritis (OA). Mendelian randomization analysis provided evidence for a positive causal effect of genetic predisposition to RA on asthma (inverse-variance weighted odds ratio = 1.037, 95% confidence interval = 1.007–1.068), but found no significant causal effect for OA. This study provides dual evidence supporting a significant and potentially causal relationship between RA and asthma. In contrast, the association with OA appears to be noncausal, likely driven by confounding factors.