Elsevier

Social Science & Medicine

Volume 66, Issue 7, April 2008, Pages 1579-1587
Social Science & Medicine

Quality of life, health and physiological status and change at older ages

https://doi.org/10.1016/j.socscimed.2007.12.021Get rights and content

Abstract

The relationship between self-reported health status and quality of life at older ages is well established. The present paper investigates this relationship further, using objective measures of health and their change over time in the English Longitudinal Study of Ageing, where positive quality of life at older ages was measured as CASP-19. Cross-sectionally, lung function and obesity, but not blood pressure, were associated with quality of life; these relationships in path analysis were transmitted primarily via functional limitation and more modestly, and only for lung function, via clinical depression. Longitudinally, the results suggest a stable and long-term influence on quality of life of lung function and, among women, body mass index, to which the influence of change may be cumulative; longer follow-up is required to clarify these processes. Overall, the results show that the relationship between health and quality of life is independent of potential psychological confounders, that functional limitation is the key dimension of health in its relationship with quality of life and that clinical depression may be an important mediator between functional limitation and quality of life.

Introduction

Most studies of life at older ages have found that a person's health is associated strongly with their quality of life (Bowling, 1996, Bowling et al., 2004, Farquhar, 1995, Gabriel and Bowling, 2004, Netuveli et al., 2005, Netuveli et al., 2006, Townsend, 1957, Wiggins et al., 2004). All of these studies relied on respondents' self-reports of health status, functional limitation, activities of daily living and so forth, which leaves the at least theoretical possibility that some third variable, say clinical depression, was influencing the self-reports of both health and quality of life. A previous publication tried to control this possible source of bias by repeating the analyses after excluding respondents who were clinically depressed, with substantively unchanged results (Netuveli et al., 2005). The present paper furthers the process of control by using objective measures of health.

Health is a complex concept, whose measurement can be biased easily by various aspects of illness behaviour such as the demands of everyday life, the assumptions and understandings of lay referral systems and the use and quality of medical care (Blane et al., 1996, Blaxter, 1990, Blaxter and Patterson, 1982, Herzlich, 1973). Objective measures of physiological status offer a way around the problem of illness behaviour, especially when the measurements are made on a random sample of the general population. The three classic measures of physiological status used in field surveys are non-invasive; they are blood pressure, lung function and body mass index, which is a function of height and weight. These aspects of physiological status occupy an interesting mid-point between health and disease. At their extremes, they constitute disease-like conditions: hypertension and, in some countries, hypotension; respiratory dysfunction and failure; obesity and underweight. At the same time, most people lie within these extremes, where their status on each of these measures is an objective component of their health; hence the use of these measures for occupational and insurance purposes, in general practice surgeries and in epidemiological field surveys. As well as controlling for third variable bias, analysis of physiological status in consequence will suggest which of these dimensions of health is important to quality of life.

The medical literature contains other studies of physiological status and quality of life. The originality of the present paper derives from three sources. First, its use of the CASP measure of positive quality of life at older ages (explained in the methods section), which concentrates on the beneficial and enjoyable aspects of ageing and avoids limiting interest in older people to their demand for health and social care. The medical literature, in contrast, tends to be interested in health-related quality of life, which is a more limited and negative concept. Further, with questionable validity (is quality of life the same as health?), it tends to equate health-related quality of life with physical and mental functioning, measured by, for example, SF-36 (Banegas et al., 2006, Yancy et al., 2002). The CASP measure aims to avoid these problems by focusing on the positive aspects of life at older ages and by being independent of health and other factors that might influence it. Second, unlike the medical literature which concentrates on single, speciality-specific, objective measures (blood pressure for hypertension studies, lung function for respiratory studies; and body mass index for obesity studies), the present paper is concerned with general health as indexed by the three objective measures generally used in non-invasive field surveys. Finally, the presently analysed survey so far has recorded twice these objective measures, several years apart, so the relationship between change in objective health and positive quality of life at older ages can be examined.

The present article's research questions follow from this brief review. (1) Is the relationship between health and quality of life replicated when health is measured objectively? (2) If yes, in this relationship, what is the relative importance of blood pressure, lung function and body mass index; and what are the pathways by which these relationships are mediated? (3) What do these results tell us about the relationship between health and quality of life at older ages?

Section snippets

Data

The analyses reported in the present paper use data from the English Longitudinal Study of Ageing (ELSA), a large multi-purpose study that is following all respondents aged 50 years or more in the Health Surveys for England of 1998, 1999 and 2001 (Banks et al., 2006, Marmot et al., 2003), referred to, in the present paper, as ELSA Wave 0. All three of these Health Surveys measured blood pressure and height and weight, from which body mass index has been calculated (weight in kilos divided by

Results

Table 1 compares the socio-demographics of the ELSA Wave 2 subjects with their non-institutionalised age peers within the whole population of England, as recorded at the 2001 Decennial Census; comparison was limited to the few census items reported separately for the non-institutionalised population. The ELSA Wave 2 sample slightly over-represents women (55.5% vs. 53.7%); under-represents the age group 50–64 years (48.2% vs. 53.3%); considerably under-represents those with access to a motor

Discussion

Our first research question was: Is the relationship between health and quality of life replicated when health is measured objectively? to which Table 2 answers yes in the case of lung function and obesity, but not for blood pressure. This result suggests that the cross-sectional association found in previous studies between self-reported health and self-reported quality of life is not due to both self-reports being influenced by some third variable such as psychological outlook or mental

Acknowledgments

We acknowledge with gratitude the Economic & Social Research Council, whose Award Number L326253061 funded this work. We are grateful also to the English Longitudinal Study of Ageing research team at National Centre for Social Research, Institute of Fiscal Studies and University College London, whose hard work produced this excellent data set.

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