Cognitive function assessed by Mini-mental state examination and risk of all-cause mortality: a community-based prospective cohort study

Background The Mini-Mental State Examination (MMSE) is the most widely used instrument to test cognitive functioning. The present study prospectively investigated the association between MMSE scores, MMSE domains, and all-cause mortality. Methods A total of 2134 participants aged 60 years or over, selected from one urban community-dwelling population in China, were enrolled in the study. The cognitive test was performed by use of the MMSE at baseline, and covariates were recorded simultaneously. Cox regression models were used for examining the cognitive function, expressed by different MMSE transformations, and all-cause mortality. After followed up for a median of 10.8 years (ranging from 1.0 to 11.3 years), loss to follow-up was 13.1% and 1854 individuals were finally included in the analyses. Results The subjects had the mean (SD) age of 71.01 (7.00) years, and 754 (40.67%) of them were women. Per point increase on MMSE scores was associated a 4% decreased risk of all-cause mortality [hazard ratio (HR): 0.96; 95%confidence interval (CI): 0.93-0.98]; compared to MMSE scores of >= 24, MMSE scores of < 24 was associated with a 43% increased risk of all-cause mortality (HR: 1.43; 95% CI: 1.05-1.95); compared to MMSE scores of 30, MMSE scores of 27-29 (HR: 1.27; 95% CI: 0.89-1.82), 24-26 (HR: 1.30; 95% CI: 0.86-1.99), and < 24 (HR: 1.79; 95% CI: 1.15-2.77) had a graded increase in risk of all-cause mortality (p for trend =0.003). Of MMSE domains, orientation to time (HR: 2.00; 95% CI: 1.29-3.11), attention and calculation (HR: 1.49; 95% CI: 1.16-1.92), recall (HR: 2.59; 95% CI: 1.22-5.47), and language (HR: 1.68; 95% CI: 1.25-2.26) were significantly associated with all-cause mortality in the unadjusted model; for one increase in the number of impaired MMSE domains, the unadjusted HR (95% CI) of mortality is 1.51 (1.38, 1.65), and the HR (95% CI) of mortality is 1.12 (1.01, 1.25) with full adjustment; compared to 0 and 1 impaired MMSE domains, the HRs of all-cause mortality associated with 2, 3, 4, and >= 5 impaired MMSE domains were 1.14 (95% CI: 0.84-1.54), 1.50 (95% CI: 0.98-2.28), 2.14 (95% CI: 1.12-4.09) and 2.29 (95% CI: 1.24-5.04), respectively, and a dose-dependent relationship was significant (p for trend =0.003). Conclusion Cognitive impairment is associated with the increased risk of all-cause mortality in the Chinese elderly. Similarly, reduced MMSE scores, as well as impaired MMSE domains, are also associated with the increasing risk of all-cause mortality.