Does the association between self-rated health and mortality vary by social class?
Introduction
Self-rated health (SRH) refers to a single item health measure that asks individuals to rate their health as excellent, good, moderate or poor. SRH is generally considered to be a valuable source of information on subjective health status and is popular due to its simplicity to collect. It declines with age and has strong associations with all-cause mortality that are not explained by existing known disease (Appels et al., 1996, DeSalvo et al., 2006, Grant et al., 1995, Heidrich et al., 2002, Helmer et al., 1999, Idler, 1999, Idler and Angel, 1990, Idler and Benyamini, 1997, Jylha et al., 1998, Miilunpalo et al., 1997, Mossey and Shapiro, 1982, Singh-Manoux et al., 2007). There are a number of potential explanations for this relationship between SRH and mortality (DeSalvo et al., 2006). SRH may act as a proxy for other covariates that are known to predict health (DeSalvo et al., 2006); it may show sensitivity to preclinical disease not captured by disease or risk factor measures (Idler & Benyamini, 1997); it may reflect experiential knowledge of health, developed and refined through firsthand experience (Idler, Leventhal, McLaughlin, & Leventhal, 2004); or it may reflect judgements about future health trajectories rather than just current health levels, perhaps by influencing health behaviours that influence mortality risk (DeSalvo et al., 2006, Idler and Benyamini, 1997, Idler et al., 2004).
In any single-index self-reported measure of health, response styles and reference levels against which health is judged may vary between respondents (Groot, 2000, Jürges, 2004, Jürges, 2007, Krause and Jay, 1994). Several studies have investigated whether the predictive ability of SRH varies by subgroups such as age or sex, however, few have examined the role of socioeconomic factors. It is plausible that individuals in different social classes with similar physical health status may use different criteria to judge their health, potentially emphasising different aspects of health when evaluating the question (Huisman, van Lenthe, & Mackenbach, 2007), thus the SRH–mortality relationship may vary by social class. The few published studies investigating whether SRH is similarly related to subsequent mortality in different social classes have shown mixed results. Two Swedish studies (Burstrom and Fredlund, 2001, van Doorslaer and Gerdtham, 2003) found that the relationship between SRH and mortality did not differ by occupational group or income. Two recent studies in the Netherlands (Huisman et al., 2007) and the USA (Beam Dowd & Zajacova, 2007) suggest a stronger association in those of high socioeconomic status (SES), while a French study (Singh-Manoux et al., 2007) found that the predictive ability of SRH for mortality weakened with increasing socioeconomic advantage. We examine the relationship between SRH and mortality by occupational social class in a large population-based study in the UK.
Section snippets
Participants
The participants were part of a prospective population study of men and women aged 39–79 years, resident in Norfolk, United Kingdom, an area which encompasses a wide socioeconomic and urban–rural distribution. General practice age–sex registers were used to recruit the cohort between 1993 and 1997 as part of the European Prospective Investigation of Cancer; as virtually 100% of people in the UK are registered with general practitioners through the National Health Service, the age–sex registers
Results
Descriptive characteristics of the cohort at baseline are shown in Table 1. Men were on average slightly older and had higher BMIs than women. The proportion of current smokers in each sex was similar, a greater proportion of men were former smokers, while a greater proportion of women have never smoked. A much larger proportion of men finished school. The proportions in each category of SRH were similar in men and women. There was a higher prevalence of diabetes and high cholesterol in men,
Discussion
There was a strong relationship between poor SRH and mortality in both men and women, with higher mortality rates in those with lower SRH. As in other studies (Idler & Benyamini, 1997), SRH predicted future mortality after adjustment for age, and health-related covariates, BMI, smoking, physical activity, alcohol intake, prevalence of diabetes, high blood pressure, high cholesterol, and educational level. Our results show a similar relationship between SRH and mortality in manual and non-manual
Conclusions
In this middle-aged and elderly population, self-rated health appears to predict mortality in a similar manner in non-manual and manual classes. At present SRH appears to provide a powerful measure that may help identify at-risk individuals and is a sensitive indicator of unknown factors that relate to increased mortality risk.
Competing interests
None declared.
Acknowledgements
We thank the participants and general practitioners who took part in the study and the staff of EPIC-Norfolk. This project receives support from the National School of Primary Care Research. EPIC-Norfolk is supported by research programme grant funding from the Medical Research Council and Cancer Research Campaign, with additional support from the Stroke Association, British Heart Foundation and Research Into Ageing.
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