Background: Both obesity and low income are risk factors of asthma and their joint effect on the disease has not been studied previously.
Objective: To examine the influence of obesity and household income and their joint effect on asthma.
Methods: The authors conducted an analysis based on data from 115,722 subjects 18+ years of age who participated in a national survey in 2005. Logistic regression analysis was used to adjust for covariates. The joint effect of household income and body mass index (BMI) on asthma was assessed on an additive scale.
Results: Obesity associated with an increased risk of asthma was significant in all income categories in women but was only significant in the low-income group in men. A stronger association between obesity and asthma was observed in low- than in high-income families. For men and women combined, the adjusted odds ratio for those with a BMI value of 35 kg/m(2) or more versus those with a BMI less than 25 kg/m(2) was 2.01 in the low-household income group compared with only 1.47 in the high-income group. The corresponding adjusted relative excess risk of interaction was 1.50 (95% confidence interval [CI]: 0.88, 1.65) for men and women combined and was 2.73 (95% CI: 1.50, 5.39) for women.
Conclusion: These data suggested an interactive effect of obesity and low-household income on the prevalence of asthma.