The effect of comorbidities on survival in persons with Alzheimer's disease: a matched cohort study

Alzheimer's disease (AD) is one of the leading causes of death world-wide, but little is known on the role of comorbidities on mortality among people with AD. We studied how comorbidities and age at AD diagnosis impact the survival of people with AD. The Medication Use and Alzheimer's disease (MEDALZ) cohort study included 70,718 community-dwelling persons in Finland with AD diagnosis from 2005 to 2011 and were matched 1:1 (age, gender, and hospital district) to people without AD (mean age 80 years, 65% women, and the mean follow-up 4.9 and 5.6 years, respectively). Covariates (age, gender, and socioeconomic position), comorbidities (cardiovascular disease, stroke, diabetes, asthma/ chronic obstructive pulmonary disease (COPD), hip fracture, cancer treatment, and mental or behavioral disorders excluding dementia) and survival data were obtained from nationwide registers. Cox proportional hazard models were used to compare risk of death between people with and without AD. During the follow-up period a greater proportion of the AD cohort died compared to the non-AD cohort (63% versus 37%). In both cohorts, older age, male gender, lower socioeconomic position, and history of comorbidities were associated with shorter survival and higher risk of death. The associations of comorbidities with survival is weaker in the older age groups and people with AD. Hip fracture (adjusted HR 1.35, 95% CI 1.30-1.41), stroke (1.30, 1.27-1.34), and recent cancer treatment (1.29, 1.26-1.32) had the strongest associations in the AD cohort. Age modified the associations in both cohorts (weaker associations among older people). Alzheimer's disease is the major factor affecting survival, but comorbidities further decrease survival also in individuals with Alzheimer's disease. Therefore, appropriate management of care of these comorbidities might affect not only survival but also the wellbeing of this vulnerable population.