Cognitive impairment: an independent predictor of excess mortality: a cohort study

Abstract

Background: Dementia is a leading cause of death among older adults, but less is known about the mortality risk associated with milder forms of cognitive impairment.

Objective: To determine whether cognitive impairment is independently associated with increased long-term mortality in primary care patients aged 60 years and older.

Design: Linkage of electronic health records from a cohort recruited between January 1991 and May 1993 with data from the National Death Index through 31 December 2006.

Setting: A public safety-net hospital and its community health centers.

Patients: 3957 older adults aged 60 to 102 years who were screened at scheduled primary care appointments.

Measurements: At baseline, patients were screened for cognitive impairment by using the Short Portable Mental Status Questionnaire and were categorized into groups with no, mild, or moderate to severe cognitive impairment. Baseline data from comprehensive electronic health records were linked with vital status obtained from the National Death Index. Kaplan-Meier survival curves compared time to death for the groups with cognitive impairment. Cox proportional hazards models controlled for mortality risk factors.

Results: At baseline, 3157 patients had no cognitive impairment, 533 had mild impairment, and 267 had moderate to severe impairment. Overall, 2385 of the 3957 patients (60.3%) died during the observation period: 1812 (57.4%) patients with no cognitive impairment, 363 (68.1%) patients with mild impairment, and 210 (78.7%) patients with moderate to severe impairment. Both mild and moderate to severe cognitive impairment were associated with increased mortality hazard independent of other mortality risk factors (hazard ratio, 1.184 [95% CI, 1.051 to 1.334] and for mild impairment 1.447 [CI, 1.235 to 1.695] for moderate to severe impairment). Median survival for all 3957 participants was 129 months. Median survival for participants with no, mild, and moderate to severe cognitive impairment was 138, 106, and 63 months, respectively.

Limitations: Cognition was assessed only at enrollment by using a screening instrument. Participants were drawn from a single safety-net health system and had low educational and socioeconomic status, which limits generalizability to other populations. Changes in cognition, function, and comorbid conditions were not measured over time.

Conclusion: Both mild and moderate to severe cognitive impairment as identified by the Short Portable Mental Status Questionnaire are associated with an increased risk for mortality.

Primary funding source: Agency for Healthcare Research and Quality.