Increased risk of depression in COPD patients with higher education and income.

This study examined potential modifying effects of income and education on the relationship between chronic obstructive pulmonary disease (COPD) and depression. The analysis was based on 44,963 Canadians aged 35 years or more who participated in the Canadian National Population Health Survey in 1996-1997. Logistic regression analysis was used to examine the association between prevalence of depression and COPD according to sex, income adequacy or educational level. We used a bootstrap procedure to take sampling weights and design effects into account. People with COPD had twice the prevalence of depression compared to those without COPD. The association tended to be stronger in well-educated men [adjusted odds ratio (OR) = 3.02, 95% confidence interval (CI) = 1.04, 8.75] and women (OR = 2.60, 95% CI = 1.55, 4.38) than those less educated (men: OR= 1.19, 95% CI = 0.47, 3.05; women: OR = 1.93, 95% CI = 0.96, 3.87). An increased prevalence of depression associated with COPD was also found in women with higher household income (adjusted odds ratio = 4.57, 95% CI = 2.27, 9.19) than those with lower income. However, this pattern was not found in men. In conclusion, COPD patients with higher education are more likely to be depressed. The modifying effect of income may vary by gender. Possible reasons for these findings are explored.