Determinants of self-rated health: Could health status explain the association between self-rated health and mortality?

Abstract

The purpose of this study was to investigate factors related to self-rated health and to mortality among 2490 community-living elderly. Respondents were followed for 7.3 years for all-cause mortality. To compare the relative impact of each variable, we employed logistic regression analysis for self-rated health and Cox hazard analysis for mortality. Cox analysis stratified by gender, follow-up periods, age group, and functional status was also employed. Series of analysis found that factors associated with self-rated health and with mortality were not identical. Psychological factors such as perceived isolation at home or ‘ikigai (one aspect of psychological well-being)’ were associated with self-rated health only. Age, functional status, and social relations were associated both with self-rated health and mortality after controlling for possible confounders. Illnesses and functional status accounted for 35–40% of variances in the fair/poor self-rated health. Differences by gender and functional status were observed in the factors related to self-rated health. Overall, self-rated health effect on mortality was stronger for people with no functional impairment, for shorter follow-up period, and for young-old age group. Although, illnesses and functional status were major determinants of self-rated health, economical, psychological, and social factors were also related to self-rated health.

Introduction

Usefulness of self-rated health in predicting mortality and functional decline has been well documented in studies conducted in Western and Asian nations (Idler and Kasl, 1995, Idler and Benyamini, 1997, Lee, 2000). These studies found that those rated their own health poorer had significantly higher risk of functional decline or death after adjustment for possible confounders such as demographics, health status, and social factors. Protective effect of self-rated health on functional decline or mortality seems quite consistent across populations. However, regarding sub-group differences in self-rated health effect, studies found inconsistent results so far. Overall, the effect of self-rated health on mortality was found stronger for men (Deeg and Kriegsman, 2003, Idler, 2003, Spiers et al., 2003). However, there are studies reporting stronger effect for women (McCallum et al., 1994, Sugisawa and Sugisawa, 1995). Differences in the effect of self-rated health on mortality by different follow-up periods were also observed. Although generally stronger effect was found for shorter follow-up period (Benyamini et al., 2003), another study in Japan found a stronger effect for longer follow-up period (Haga et al., 1995).

One explanation for such inconsistent results is that self-rated health is a more inclusive measure of health covering wider aspect of social or psychological factors (Idler and Benyamini, 1997). Although illnesses and functional status were reported as main determinants of self-rated health (Kaplan et al., 1996, Damian et al., 1999), economic or social factors were also associated with self-ratings of health (Idler and Benyamini, 1997). A recent study in Taiwan concluded that clinical measures predicted diverse aspects of well-being among the elderly less powerfully than self-ratings of health (Goldman et al., 2003).

In the current study, we tested the hypothesis that self-rated health reflects wider aspects of health including physical, psychological, and social factors. Logistic regression analysis investigated factors associated with self-rated health. In addition, we employed a series of Cox regression analysis by gender, follow-up period, age group, and functional status to see if self-rated health effect on mortality differs by population. Interactions between various factors and self-rated health were also tested.