Research reportDepression and physical health in later life: results from the Longitudinal Aging Study Amsterdam (LASA)
Introduction
In both cross-sectional and longitudinal studies, late life depression and physical health have been found to be closely related (Gurland, 1983, Murrell et al., 1983, Schulberg and Saul, 1985, Berkman et al., 1986, Kennedy et al., 1989, Kennedy et al., 1991, Cole, 1990, Beekman et al., 1995a, Beekman et al., 1995b). Compared with younger adults, the importance of declining physical health as a risk factor for depression increases in later life. Indeed, previous studies suggest that the effect of ill health overwhelms the impact of other risk factors in later life (Kennedy et al., 1989, Prince et al., 1997).
Although the association between physical health and depression is firmly established, a number of issues remain unresolved. The first of these concerns the heterogeneity of late life depression (Caine et al., 1994). Clinical heterogeneity is reflected by the fact that most of the depressive syndromes experienced by older persons do not fulfil rigorous diagnostic criteria. They are not accounted for by the diagnoses of major depression or dysthymic disorder (Snowdon, 1990, Blazer, 1994). This has led to a serious questioning of the validity of current diagnostic criteria for depression among the elderly and to ongoing controversy about the prevalence of depression in later life (Snowdon, 1990, Blazer, 1994, Beekman et al., 1995c). Consequently, it has been concluded that epidemiological studies in the elderly should include both major depression and those depressive syndromes not fulfilling rigorous diagnostic criteria. The latter group of mostly ill-defined depressive syndromes is receiving increasing attention and will be collectively named minor depression in this paper (Blazer, 1994, Tannock and Katona, 1995). The etiological heterogeneity of late life depression is reflected by the finding that major and minor depression appear to be associated with different sets of risk factors. In previous studies we found that risk factors indicative of long-standing vulnerability for depression, such as family history, previous history and personality factors, had stronger associations with major depression than with minor depression (Beekman et al., 1995c). Conversely, risk factors reflecting stresses commonly experienced in older age, such as having functional limitations, smaller contact networks and less exchange of social support, were more strongly associated with minor depression. In most previous studies depression has either been defined according to rigorous diagnostic criteria, or in broader terms, according to the level of symptoms. To address the clinical and etiological heterogeneity of late life depression, which may obscure associations with physical health, it seems necessary to define and measure depression at both levels.
A second issue is which aspects of physical health are more salient for late life depression (Kinzie et al., 1986). There are a number of diseases which have a direct etiological link with depression. The best known examples are stroke and Parkinson's disease (Eastwood et al., 1989, Cummings, 1992). However, a repeated finding of community-based studies has been that general aspects of physical health, such as the level of functional impairment and perceived health, are more important correlates of depression than specific diagnosis (Kinzie et al., 1986, Kennedy et al., 1989, Beekman et al., 1995a). For both clinical practice and public health purposes it is important to know which diseases pose a greater risk of depression, and which aspects of physical health have the stronger associations with depression.
A third issue is whether the risk of depression associated with a decline in physical health may be attenuated by factors such as social support or the presence of a partner. If so, this may lead to the formulation of treatment strategies which, recognising that chronic physical diseases can only rarely be cured, may help improve the quality of life of older people.
The primary aim of the present study was to compare the risk of major and minor depression associated with common physical illnesses and with more general aspects of physical health, such as functional limitation. Moreover, the influence of potential stress-buffering factors (Cassel, 1976), such as the presence of a partner and the presence of a contact network with which social support is exchanged (Cohen and Wills, 1985), will also be explored. The consequences these findings may have for the treatment of late life depression will be discussed in the conclusion of the paper.
Section snippets
Sampling and procedures
The Longitudinal Aging Study Amsterdam (LASA) is a 10-year longitudinal study on predictors and consequences of changes in well-being and autonomy in the older population (Deeg et al., 1993). Full details on sampling and response are described elsewhere (Beekman et al., 1995c). In short, a random sample of older (55–85) persons, stratified for age, sex and level of urbanization was drawn from the population registers in 11 municipalities in the Netherlands. The sample was used in two studies.
Characteristics of the sample
In Table 1, demographic and health-related characteristics of the sample are shown. Due to the sampling procedure men and women are roughly evenly represented. The higher proportion of older old reflects the intended even distribution of subjects 5 years into the study. The relatively high number of subjects unmarried, with cognitive impairment or physical health problems is a function of oversampling among the older old. It also shows that attrition has not caused the sample to become a sample
Discussion
The results suggest that there is an important, but not an overwhelming association between physical health and depression in later life. As in earlier studies, the more general and subjective aspects of physical health, such as functional limitations and self-perceived health, were more strongly associated with depression than specific disease categories (Kinzie et al., 1986, Beekman et al., 1995a). Because data were available covering a wide range of the known risk factors of depression in
Acknowledgements
This study was based on data collected in the context of the Longitudinal Aging Study Amsterdam (LASA), which is funded primarily by the Ministry of Welfare, Health and Sports of the Netherlands. The authors thank M.J. Prince for his valuable comments.
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