Coexisting Asthma and Diabetes Are Associated With Adverse Metabolic and Inflammatory Profiles

AIMS: Asthma and diabetes frequently co-occur and share metabolic and inflammatory features, yet the cardiometabolic profile associated with their coexistence is not well defined. We examined differences in cardiometabolic and inflammatory biomarkers by joint asthma-diabetes status in U.S. adults and evaluated whether current asthma modifies diabetes-associated alterations. METHODS: We conducted a cross-sectional analysis of 5295 non-pregnant adults aged 20-85 years from NHANES 2015-2020 with complete fasting data. Participants were categorized as having neither condition (77.0%), asthma only (7.0%), diabetes only (14.1%), or both conditions (1.9%). Survey-weighted multivariable linear regression estimated associations with glycaemic, lipid, insulin-resistance and inflammatory biomarkers. Multiplicative and additive interactions were assessed using product terms and the relative excess risk due to interaction (RERI). Models were adjusted for sociodemographic and behavioural factors and waist circumference. RESULTS: Participants with both asthma and diabetes displayed the most adverse biomarker profile. Compared with those with neither condition, the comorbid group had higher fasting glucose (β 58.86 mg/dL, 95% CI 45.49-72.23), HbA1c (β 1.70%, 95% CI 1.38-2.03), HOMA-IR (β 5.93, 95% CI 3.43-8.42), TyG index (β 0.75, 95% CI 0.56-0.95) and ln(triglycerides) (β 0.35, 95% CI 0.14-0.56). The largest differences were observed for inflammatory markers, including ln(hs-CRP) (β 0.74, 95% CI 0.35-1.12) and hs-CRP (β 6.88 mg/L, 95% CI 2.08-11.67). Adjusted predicted means for fasting glucose (158.8 mg/dL, 95% CI 144.9-172.8) and HbA1c (7.07%, 95% CI 6.74-7.41) were also highest in the comorbid group. Multiplicative interaction tests indicated no interaction for glycaemic or lipid outcomes; significant interactions were limited to HDL-C (p = 0.039) and SIRI (p = 0.003), both reflecting sub-additive effects. No additive interaction remained significant after multiple-testing correction. CONCLUSIONS: Coexisting asthma and diabetes are associated with a substantially greater burden of dysglycaemia, insulin resistance and inflammation than either condition alone. However, formal interaction analyses suggest that these joint effects are not synergistic and instead follow additive or sub-additive patterns.