Increased risk of mortality in Alzheimer's disease patients with higher education? A replication study

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Abstract
The objective of this study was to replicate findings from an earlier study by Stern et al. of an increased risk of mortality in Alzheimer's disease (AD) patients with higher levels of education and to compare this risk with the risk of death in the elderly population. As part of a community-based follow-up study on dementia (Amsterdam Study of the Elderly[AMSTEL]) a cohort of 4,051 noninstitutionalized elderly age 65 to 84 years stratified in four 5-year strata of equal size was screened for dementia using the MMSE (Mini-Mental State Examination). Those suspected of dementia received diagnostic evaluation using the CAMDEX (Cambridge examination for mental disorders in the elderly). Clinical diagnoses of probable AD were made according to NINCDS-ADRDA criteria. Thirty-six prevalent patients were diagnosed as having AD. The suspected subcohort was followed up yearly over a period of 4 years. During the three yearly follow-ups, 30 incident patients received a diagnosis as well. After 6 years mortality data were obtained from municipality records. Cox proportional hazards models adjusted for age and sex were used to estimate the relative risk of death associated with the level of education. Relative risk of death decreased (although not statistically significant) in AD patients as level of education increased (RR= 0.86; 95% CI, 0.63 to 1.19). In the full baseline sample, relative risk of death decreased as level of education increased (RR = 0.86; 95% CI, 0.89 to 0.97). In this study we could not replicate the findings of Stern et al. of an increased risk of death in more highly educated AD patients. Several major differences between the two studies, among which difference in populations used is considered to be most important, are discussed that might explain the conflicting results. We conclude that higher education is not associated with increased risk of mortality in AD patients.