Background: While cross-sectional and longitudinal studies have consistently found depressive illness and disability to be related, understanding whether depression leads to subsequent onset of disability is limited.
Methods: In the context of the multi-centre international WHO Collaborative Study on Psychological Problems in General Health Care, we followed prospectively consulting non-elderly primary care patients who were essentially disability free at baseline but who differed in baseline depression status, comprising 1051 patients free of physical disability at baseline including 14% depression; 914 free of social disability including 9% depression. Depression status was assessed with the CIDI; patient-reported physical disability with the MOS physical functioning scale and social disability with the BDQ role functioning and number of disability days measures; investigator-rated social disability with the Occupational section of Groningen Social Disability schedule; and the treating physicians rated the severity of physical illness.
Results: In patients essentially disability free at baseline, depressive illness resulted in a 1.5-fold (at 3 months) and a 1.8-fold (at 12 months) increase in risk of onset of physical disability, after controlling for physical disease severity. Depressive illness also resulted in a 2.2-fold (at 3 months) and a 23-fold (at 12 months) increase in risk of onset of social disability, after controlling for physical disease severity, physical disability and onset of physical disability.
Conclusions: Among non-elderly primary care patients, depressive illness is associated with onset of physical disability and shows an even stronger association with onset of social disability.