The effect of psychiatric co-morbidity on cognitive functioning in a population-based sample of depressed young adults.

BACKGROUND: Psychiatric co-morbidity is often inadequately controlled for in studies on cognitive functioning in depression. Our recent study established no major deficits in cognition among young adults with a history of pure unipolar depression. The present study extends our previous work by examining the effects of psychiatric co-morbidity and other disorder characteristics on depression-related cognitive functioning.

METHOD: Performance in verbal and visual short-term memory, verbal long-term memory and learning, attention, processing speed, and executive functioning was compared between a population-based sample aged 21-35 years with a lifetime history of unipolar depressive disorders (n=126) and a random sample of healthy controls derived from the same population (n=71). Cognitive functioning was also compared between the subgroups of pure (n=69) and co-morbid (n=57) depression.

RESULTS: The subgroups of pure and co-morbid depression did not differ in any of the cognitive measures assessed. Only mildly compromised verbal learning was found among depressed young adults in total, but no other cognitive deficits occurred. Received treatment was associated with more impaired verbal memory and executive functioning, and younger age at first disorder onset with more impaired executive functioning.

CONCLUSIONS: Psychiatric co-morbidity may not aggravate cognitive functioning among depressed young adults. Regardless of co-morbidity, treatment seeking is associated with cognitive deficits, suggesting that these deficits relate to more distress.