Socioeconomic inequalities in physical and mental functioning of Japanese civil servants: Explanations from work and family characteristics

Abstract

Poor physical and mental functioning is more common among people of low socioeconomic status (SES) and those with disadvantaged work and family characteristics. This study aims to clarify whether the SES inequalities in functioning can be explained by the SES differences in work and family characteristics. The subjects were 3787 male and female civil servants, aged 20–65, working in a local government on the west coast of Japan. Logistic regression analysis was performed to examine (1) whether there were employment-grade (SES) differences in poor physical and mental functioning as measured by the Short Form 36 (SF-36) and (2) whether these SES differences were explained by work and family characteristics. In general, low control at work, high demands, low social support, short and long work hours, shift work, being unmarried, high family-to-work conflict and high work-to-family conflict were independently associated with poor physical and mental functioning in both men and women. In men, the age-adjusted odds ratio (OR) of low-grade employees for poor physical functioning was 1.93 (95% confidence interval: 1.38–2.69) in comparison to high-grade employees. The grade difference was mildly attenuated, when adjusted for work and family characteristics (OR=1.72)(1.20–2.47). The age-adjusted OR of the low-grade employees for poor mental functioning was 1.88 (1.29–2.74). The grade difference was attenuated and no longer significant when adjusted for work and family characteristics (OR=1.51)(0.99–2.31). Among women, there were no significant grade-differences in poor physical and mental functioning. Although longitudinal research is necessary to clarify the causal nature of these associations, improvements in SES differences in work and family characteristics may be important for reducing SES inequalities in physical and mental functioning among Japanese men. The different patterns of SES inequalities in health between men and women deserve further research.

Introduction

The widening gap in mortality rates among socioeconomic status (SES) groups is of major public health concern (Acheson, 1998; Mackenbach et al., 2003). In Japan, despite an overall reduction in mortality rates, a gap in mortality rates among occupation groups has increased between 1990 and 2000, particularly among men (The Ministry of Health, Labour, and Welfare, 2003). Although the established coronary risk factors such as cigarette smoking, hypertension, and hypercholesterolemia are more common in low SES groups, these differences do not account for more than a third of the social gradients in cardiovascular disease in the first Whitehall study (Marmot, Shipley, & Rose, 1984). In addition, the international MONICA studies indicate that the international variations in the three established coronary risk factors account for less than half of the international variations in coronary heart disease mortality rates (The World Health Organization MONICA Project, 1994). Consequently, other potential risk factors that could explain the social inequalities in health, including work characteristics and deprivation in early life, have been investigated (Bosma et al., 1997; Kuh, Hardy, Langenberg, Richards, & Wadsworth, 2002).

Karasek (1979) reported that excessive psychological work demands with lack of decision latitude (low control) had links with the risk of stressful experience. Karasek and his colleagues also found that high-demand low-control conditions were associated with an increased risk of coronary heart diseases in Swedish men (Karasek, Baker, Marxer, Ahlbom, & Theorell, 1981). Since then, a number of epidemiological studies have shown that stressful work characteristics are associated with cardiovascular risks and diseases (Theorell & Karasek, 1996). Their original model was later modified to include social support at work as a third dimension (Johnson & Hall 1998). To date, it has been reported that low control at work, high demands, and low social support are associated with increased risks of coronary heart diseases (Bosma et al., 1997), musculoskeletal diseases (Hoogendoorn, van Poppel, Bongers, Koes, & Bouter, 2000), and depression (Paterniti, Niedhammer, Lang, & Consoli, 2002). Based on a cohort study of British civil servants, North et al. (1993) reported that approximately 25% of the social gradient in long spells of sick leave in men and 35% of the social gradient in women was accounted for by age, health behaviours, and work characteristics. Because low control and low social support at work are more common among the low SES groups (Marmot et al., 1991), such disadvantaged work characteristics may contribute to social inequalities in health.

Family life is another important component of adult life (Martikainen, 1995). Employed men and women may have multiple roles as employee, spouse, and parent. These multiple roles can be hypothesized to have a health-promoting or health-damaging impact (Martikainen, 1995). While the women's labour force participation rate has risen from approximately 35% in the 1950s to 65% in the 1990s in the US and European countries, the rate has been near to 55% in Japan (Flath, 2000). However, with a shift of the main industries from agriculture to manufacture in Japan, the type of employment has considerably changed from family enterprise to employees in larger scale enterprises (Flath, 2000). In addition, the time devoted to taking care of children and the household has increased among Japanese men (Statistics Bureau, 2001). These changes may have resulted in increased conflict between the demands of work and the family roles of men and women (Frone, 2000). Such changed psychosocial conditions of the family environment may have some effect on health and contribute to the social inequalities in health.

Although the associations of work and family characteristics with health have been investigated in many European and North American countries (Amick et al., 1998; Stansfeld, Bosma, Hemingway, & Marmot, 1998), there have been relatively fewer studies in Japan (Chandola et al., 2004). Furthermore, there have been few studies investigating the overall health effects of work and family characteristics simultaneously, and the impact of these characteristics on social inequalities in health.

The purpose of this study is, therefore, to examine in a population of Japanese civil servants (1) whether there are SES differences in work and family characteristics and poor health (2) whether work and family characteristics contribute to poor health, and (3) how much of the SES differences in poor health are explained by SES differences in work and family characteristics. Although the civil servants include a relatively limited range of SES groups, their hierarchy of income and rank is well defined and the civil service may, therefore, be an appropriate population for the purposes of this study.