Research report
Risk factors for depression in later life; results of a prospective community based study (AMSTEL)

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Abstract

Background: Depression in the elderly was found to be associated with a variety of risk-factors in cross sectional designs. Based on the vulnerability-stress model, etiologic pathways for depression have been suggested, with vulnerability modifying the effect of stress factors. The current prospective study tests an etiologic model for depression incidence, by assessing modifying effects of three types of vulnerability: genetic/familial vulnerability, organic vulnerability, and environmental vulnerability. Methods: 1940 non-depressed community-living elderly were interviewed at baseline, and at follow-up three years later. Bivariate and multivariate relationships between risk factors and incident depression (GMS–AGECAT) were studied. Results: Higher age, personal history of depression, death of spouse, health related factors and comorbid organic or anxiety syndrome showed significant bivariate associations with depression incidence. In multivariate analysis, the effect of stress factors on incident depression was not modified by a genetic/familial vulnerability, nor by an organic vulnerability. Effect modification by environmental factors was however evident; having a marital partner, and if unmarried having social support, significantly reduced the impact of functional disabilities on the incidence of depression. Limitations: The study consisted of two measurements with a three years interval, depressive episodes with a short duration may be under-represented. Conclusions: In the elderly, the effect of stress on incident depression is modified by environmental vulnerability. No evidence was found of effect modification by either genetic/familial or organic vulnerability. The results have implications for both recognition and treatment of late-life depression.

Introduction

Current knowledge about risk factors of late-life depression is largely derived from either clinical populations, or from cross-sectional studies in the community. Studies of clinical patients have the disadvantage of not being representative of the vast majority of depressive subjects in the community. Cross-sectional studies in the community suffer from methodological limitations such as recall and report bias in depressed subjects (Raphael and Cloitre, 1994), and contamination of the results as risk factors are not measured independently from depression. Temporal relations remain unclear since a characteristic found to be associated with depression may have antedated (or caused) the disorder, but it may also be its consequence. Likewise, cross-sectional designs cannot distinguish whether a characteristic has prognostic value for the course of depression once depression is present, or is actually associated with its aetiology. Finally, in cross-sectional designs chronic depression is over-represented, which may bias findings with regard to aetiology.

Prospective studies of the incidence of depression among the elderly are relatively scarce and have used different sets of risk factors and research methods. Green et al. (1992) found lack of satisfaction with life, feelings of loneliness and smoking to be significantly associated with the development of depression as measured by GMS–AGECAT three years later in a cohort of community living elderly. Multivariate analysis yielded two more factors; female gender, and bereavement of a close person within six months of the third-year diagnosis. Phifer and Murrell (1986) found the incidence of significant depression in a six months period to be closely associated with changes in physical health. Kennedy et al. (1990) also found aspects of physical health to be closely related to incidence of depression in a large sample of community-dwelling elderly in a two year follow-up. In a one year follow-up study with 3-monthly assessment of depressive symptomatology by Beekman et al. (1995a), depression incidence was also found to be associated with health related variables. A recent publication by Prince et al. (1998) revealed disablement, and more specifically handicap, to be the chief cause of onsets of depression in late-life in a one-year follow-up of community living elderly.

According to the Brown and Harris (1978) etiologic model, depression in adults may be the result of ‘social stress’ factors such as life events (loss) or long term difficulties, combined with vulnerability/protective factors such as social disadvantage, lack of intimate relationships, early traumatic life events, lower intelligence/education, personal history of depressive illness and family history. Earlier cross-sectional work from the Amsterdam Study of the Elderly (AMSTEL) (Van Ojen et al., 1995a, Van Ojen et al., 1995b, Van Ojen et al., 1995c) was inspired by the work of Brown and Harris. The AMSTEL data suggested three different subtypes of geriatric depression based on etiologic determinants. Early-onset depression was found to be associated with long-standing inborn susceptibility (Kendler et al., 1993a) and vulnerability due to previous episodes: ‘sensitization’ or ‘kindling’ (Post, 1992). Late-onset depression with cognitive impairment was mainly associated with the presence of organic vulnerability factors. Late-onset depression without cognitive impairment was found to be associated with factors related to current life-stresses.

The primary aim of the present study was to further investigate the aetiology of late life depression, studying incident cases in the community in a prospective longitudinal design using a comprehensive set of risk factors generally believed to be associated with depression. In this way we hoped to avoid the above-mentioned methodological pitfalls and develop more insight into the temporal and causal relations between risk factors and late-life depression. Secondly we wanted to investigate whether the differential etiologic pathways of late-life depression suggested by earlier cross-sectional data are confirmed using a longitudinal design.

Section snippets

Sampling and non-response

The population base for the study included all non-institutional individuals in the 65–84 age bracket who lived in the city of Amsterdam and were registered with a general practitioner at baseline (Van Ojen et al., 1995a). The sample was drawn from a list of 30 general practices spread throughout the city. The mean proportion of elderly individuals (15%), and the profile of the over-65 general practice-population in terms of age and gender, correspond to the non-institutionalised Amsterdam

Sample characteristics and response pattern

The demographic and functional profiles of the study sample at baseline and follow-up are presented in Table 1. Bivariate analyses showed significant differences between responders and subjects lost to follow-up on a number of baseline variables. Higher age, lower education, lower social-economic status and the existence of functional impairments, chronic disease, a lower MMSE score, an organic syndrome and depression all showed associations with non-response (p<0.001). When excluding the

Discussion

The aim of the present study was to model the aetiology of late life depression, studying incident cases in the community in a three-year prospective design. Of the subjects without depression at baseline, 15.9% had developed a GMS–AGECAT depressive syndrome at follow-up. Compared to previous studies of depression incidence in the elderly this is relatively high. Phifer and Murrell (1986) noted an incidence of 10.7% after only six months, using a Center for Epidemiologic Studies Depression

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