Asthma at mid-life is associated with physical activity limits but not obesity after 10years using matched sampling in a nationally representative sample

Asthma and obesity are both prevalent conditions that appear related, but the etiology for this association remains unclear. This study examines whether asthma is associated with obesity and physical activity limits 10years later among a subsample from the National Longitudinal Survey of Youth 1979 who were age 40 at baseline. We addressed selection bias using inverse-propensity score weighting (N=5077), and confirmed the results with full matching (N=5041), and with both methods we estimated new sampling weights so that the sample would remain nationally representative. Both matched sampling methods balanced adults with asthma versus those without asthma on all 7 covariates: baseline obesity, sex, race/ethnicity, family income, poverty status, general health status and physical activity limits. Before matching, baseline asthma was significantly associated with developing obesity 10years later in an unadjusted model [OR=1.44 (1.10-1.90)], but not in the multivariable model [OR=1.15 (0.80-1.67)]. Baseline asthma was not associated with obesity 10years later after inverse propensity weighting [OR (95% CI=1.03 (0.69-1.53)] and full matching [1.16 (0.75-1.80)]. Results remained similar after excluding subjects with baseline obesity. In a cumulative logistic model using complex survey and full matching weights, those with baseline asthma had 83% greater odds of reporting physical activity limits compared to those without asthma, OR=1.83 (1.21-2.76). Baseline asthma was not associated with obesity among either a nationally representative sample of middle-aged adults or a non-obese subset. However, asthma was associated with physical activity limits in the full matched sample. Asthma disease management programs should communicate that asthma does not imply obesity and also encourage exercise within the physical limitations of their populations. Selection bias on factors such as low socioeconomic status may explain previous asthma-obesity associations.