Socioeconomic status (SES) and perceived stress associate with increased asthma morbidity in observational studies. We investigated whether SES and perceived stress are independent risk factors for treatment failure and asthma exacerbations in a randomized clinical trial (RCT) of vitamin D and asthma morbidity.
The effect of household income (low defined as <$50,000/year), educational level (low defined as less than bachelor’s degree), and perceived stress (high defined as score of >20 on a perceived stress scale) on asthma morbidity was analyzed in 381 participants utilizing Poisson regression models. The primary outcome was treatment failure (defined in the trial protocol as a significant clinical or airflow deterioration), and the secondary outcome was asthma exacerbations requiring steroids.
54% of participants had low income, 40% had a low educational level, and 17% had high levels of perceived stress. African American race and SES (income and education) were significantly associated (p<0.001) with each other. However, their level of association still met criteria for inclusion in a regression model. After adjusting for study site, African American race, ethnicity, number of people in household, and BMI, participants with lower income had a 1.5x higher rate of treatment failure [95%CI 1.05-2.25, p=0.026] and 1.9x higher rate of asthma exacerbations [95%CI 1.12-3.33, p=0.019]. African American race and vitamin D treatment were not effect modifiers of this association. Education and perceived stress were not significantly associated with treatment failures or exacerbations.
In the context of a RCT, lower income associates with adverse asthma outcomes independent of race, education, and stress.