Investigation of possible risk factors for depression in Alzheimer's disease: A systematic review of the evidence

Abstract

Background: Depression is common in people with Alzheimer's disease (AD), and is associated with increased risk of institutionalization and mortality. Understanding risk factors for depression in AD is key to its development and treatment.

Methods: We searched the MEDLINE, EMBASE, PsycINFO, and CINAL databases for longitudinal prospective cohort studies that evaluated risk factors for depression in people with AD. Two authors independently selected articles for inclusion and assessed quality of studies using predetermined criteria.

Results: In seven studies that met the inclusion criteria, 2029 participants were followed up for a median of 5 years. Gender and educational attainment were not predictors of depression risk. History of a past psychiatric disorder and greater cognitive impairment predicted increased risk of depression in more than one study. In single studies, younger age, having a family history of psychiatric disorder, neuroticism, functional decline, presence of sleep disturbance and aggression, and increased cardiovascular risk predicted depression risk. Not being within 6 months of dementia onset and, counterintuitively having two comorbid disorders were protective factors in one study.

Limitations: A small number of studies exist overall and only a few have examined the same risk factors. Most of the studies have measured depression using scales that are not validated in AD.

Conclusions: These results inform a preliminary model of depression risk in people with AD. Unlike in the general population, men and women and those with higher and lower educational levels of attainment may be equally at risk of depression. Clinicians should be aware of these possible differences in the risk profile for depression in AD populations, to assist detection and enable early treatment. Interventions to delay cognitive and functional decline may reduce depression risk.

Keywords: Affective disorders; Affective symptoms; Alzheimer's disease; Depression; Depressive symptoms; Protective factors; Risk factors; Vulnerability.