Objective: To examine the temporal relationship between depression diagnoses and cognitive function in older medical patients.
Design: Prospective cohort study with repeated follow-up assessments at 3, 6, and 12 months after hospitalization.
Setting: The medical services of two acute care hospitals in Montreal, Quebec, Canada.
Participants: Two hundred eighty-one medical inpatients aged 65 and older without apparent cognitive impairment at study entry.
Measurements: Diagnostic Interview Schedule for depression and Mini-Mental State Examination (MMSE) for cognitive function.
Results: At study entry, 121 (43.1%) and 51 (18.1%) patients, respectively, met Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria for major or minor depression. Based on a mixed effects regression model, depression diagnoses were associated with poorer cognitive function, independent of age, education, baseline cognitive and physical function, cardiovascular diseases and other comorbidities, previous history of depression and antidepressant treatment, and fluctuation in the severity of depression symptoms over time. On average across three follow-up assessments, patients with major or minor depression, respectively, had a 0.8 (95% confidence interval: 0.1-1.5) and 1.0 (0.3-1.8) point lower performance on the MMSE than those without depression. In contrast, there was no significant association when depression diagnoses and cognitive function were assessed over shorter intervals or cross-sectionally. A general linear regression model yielded consistent results, with adjusted effect estimates of 0.9 (0.03-0.8) for major and 1.5 (0.5-2.5) for minor depression over 12 months.
Conclusion: A diagnosis of major or minor depression at hospital admission is an independent risk factor for poorer cognitive function during the subsequent 12 months in older medical patients.