Background: Obesity is a risk factor for asthma and uncontrolled asthma, and a plethora of other non-communicable diseases. However, little is known about the association between body mass index (BMI) and mortality among adults with asthma.

Aim: To compare all-cause mortality and cause of death between obese, overweight and normal weight adults with asthma.

Methods: A population-based adult asthma cohort was recruited and clinically examined between 1986 and 2001 within the Obstructive Lung Disease in Northern Sweden (OLIN) Studies. The sample (n=1970, median age 45y) was grouped into BMI categories. Underlying causes of death until 2020 were categorized as cardiovascular, respiratory, cancer and other. Hazard ratios (HR) with 95% confidence intervals (CI) for all-cause and cause-specific mortality regarding overweight and obesity were calculated via Cox proportional hazard models adjusted for age, sex, smoking habits, ischemic heart disease (IHD) and COPD at recruitment.

Results: In total, 940 individuals were normal weight, 689 overweight and 328 obese, while only 13 were underweight. Obesity increased the hazard for all-cause mortality (HR 1.36, 95%CI 1.11-1.67) and cardiovascular mortality (HR 1.54, 1.11-2.14). Obesity was however not significantly associated with respiratory (HR 0.94, 0.48-1.83), cancer (HR 1.29, 0.84-1.97) or other (HR 1.49, 0.99-2.25) mortality. Overweight did not increase all-cause or any cause-specific mortality.

Conclusion: Obesity, but not overweight, was significantly associated with increased hazard of all-cause mortality, driven by cardiovascular mortality. Neither obesity nor overweight was associated with respiratory mortality in this adult asthma cohort study.