Risk factors for functional status decline in community-living elderly people: a systematic literature review

Abstract

To lay the groundwork for devising, improving and implementing strategies to prevent or delay the onset of disability in the elderly, we conducted a systematic literature review of longitudinal studies published between 1985 and 1997 that reported statistical associations between individual base-line risk factors and subsequent functional status in community-living older persons. Functional status decline was defined as disability or physical function limitation. We used MEDLINE, PSYCINFO, SOCA, EMBASE, bibliographies and expert consultation to select the articles, 78 of which met the selection criteria. Risk factors were categorized into 14 domains and coded by two independent abstractors. Based on the methodological quality of the statistical analyses between risk factors and functional outcomes (e.g. control for base-line functional status, control for confounding, attrition rate), the strength of evidence was derived for each risk factor. The association of functional decline with medical findings was also analyzed.

The highest strength of evidence for an increased risk in functional status decline was found for (alphabetical order) cognitive impairment, depression, disease burden (comorbidity), increased and decreased body mass index, lower extremity functional limitation, low frequency of social contacts, low level of physical activity, no alcohol use compared to moderate use, poor self-perceived health, smoking and vision impairment. The review revealed that some risk factors (e.g. nutrition, physical environment) have been neglected in past research. This review will help investigators set priorities for future research of the Disablement Process, plan health and social services for elderly persons and develop more cost-effective programs for preventing disability among them.

Introduction

As recent gerontological studies indicate, health and social care services required by disabled older persons will be a growing burden and a major societal concern for the next century (Beck and Stuck, 1996; Fried and Guralnik, 1997). Although there have been recent reports about a decline in the disability rate among older people in the US, it has been estimated that from 1985 to 2050, the number of disabled older persons in and out of institutions will approximately triple (Manton et al., 1997). A reasonable response to this situation is to devise and implement strategies for preventing or delaying the onset of disability (Fries, 1980; Katz et al., 1983). In fact, trials have confirmed that community-based intervention programs can improve functional outcomes and reduce nursing home admissions in older people (Tinetti et al., 1994; Stuck et al., 1995Stuck et al., 1997). To meet the impending challenge of the 21st century, strategies for disability prevention must now be further developed.

The first step in this process is to delineate what factors convincingly lead to the development of disability. Although multiple studies have addressed this issue, the high variability among them in terms of such matters as study design and methodology makes it difficult to extract a coherent, dependable list of factors from which to develop prevention strategies. We therefore conducted a formal, systematic literature review of all longitudinal studies analyzing the association of individual risk factors with functional status outcome in community-living older subjects. The theoretical model we employed for the task of summarizing and giving structure to the evidence is the widely cited one proposed by Verbrugge and Jette (1994), a modification of a WHO model further adapted by the Institute of Medicine (World Health Organization, 1980; Pope and Tarlov, 1991). This model helps us isolate the multiple, often intertwined biological, psychological, functional, social and environmental factors that contribute to the development of disability.