Background: While considerable research exists on the role of physical illness in initiating depressive reactions, the role of depression in the onset of physical illness is much less studied. Moreover, whereas almost all previous research on depression and incident physical illness has involved specific physical illnesses, the present study examines the link between depression and incident physical illness more generally.
Methods: The study followed 388 clinically depressed patients who were entering treatment for unipolar depressive disorders and 404 matched community controls across 10 years. In self-report surveys, sociodemographic and health behavior data were indexed at baseline and physician-diagnosed medical conditions were indexed at baseline and at 1, 4, and 10 years during the follow-up period.
Results: After accounting for prior physical illness and key demographic and health behavior factors, membership in the depressed group was significantly linked to physical illness during the follow-up period. In these prospective analyses, depressed patients showed an almost two-thirds higher likelihood of experiencing physical illness during the follow-up period compared to community controls. The prospective association between depression and subsequent physical illness was evident for both less serious and more serious physical illness.
Limitations: Although participants were asked to report only physician-diagnosed conditions, the association between depression and physical illness may have been due to depressed individuals perceiving themselves as more ill than they were.
Conclusions: The World Health Organization has included the co-morbidity between depression and chronic physical illness among its ten concerns in global public health. The current findings broaden the growing awareness of the co-morbidity between depression and physical illness to encompass a vulnerability of depressed individuals to physical illness more generally.
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