Does co-morbid depressive illness magnify the impact of chronic physical illness? A population-based perspective

OBJECTIVE: To examine the relative and combined impact of depressive and chronic physical conditions on functional status and health-care use in the general population. METHOD: Canadian, representative, population-based cross-sectional survey (n=130,880). Major depressive disorder (MDD) in the past 12 months was assessed by structured interview, and physical disorders, activity reduction, role impairment and work absence by self-report. The relative impact of MDD and six common chronic physical illnesses (asthma, arthritis, back problems, chronic obstructive pulmonary disease, heart disease and diabetes) was estimated using multivariate regression, adjusting for sociodemographic characteristics and overall chronic physical illness burden. RESULTS: After adjusting for sociodemographic characteristics, alcohol dependence and chronic physical illness burden, the presence of co-morbid MDD was associated with significantly greater (approximately double the) likelihood of health-care utilization and increased functional disability and work absence compared to the presence of a chronic physical illness without co-morbid MDD. This impact of MDD was seen across each of the six chronic physical illnesses examined in this study, with the strongest associations seen for work absence. CONCLUSIONS: These observations confirm prior findings of a strong association at the population level between major depression and health-care use and role impairment among persons with chronic physical disorders. They also point to the significant impact of co-morbid major depression on health-care seeking, disability and work absence in persons with chronic physical illness, underscoring the need for greater efforts to design and test the impact of detection and treatment programs for such individuals.