Discussion

When we compared the health status and health-related behaviours of the working women and housewives in the study population, housewives had a lower risk of: anxiety about health, health dissatisfaction, a pattern of eating an insufficient breakfast, sleep problems and being uninformed about the healthcare system.

The proportion of working women receiving health check-ups was significantly higher than that of housewives. However, this result must be interpreted carefully. Workplace health check-ups are mandatory in Japan under the Occupational Safety and Health Law, and are readily available because they are often provided during working hours. Thus, a higher frequency of working women utilising the opportunity to receive health check-ups was expected. Additionally, although anxious, housewives might feel a health check-up to be less necessary than do working women. Therefore, the lower frequency of obtaining a health check-up may not necessarily mean poorer health behaviour.

Anxiety about health was an important subjective symptom among the working-age population because this cohort was exposed to many sources of psychological distress.29 As previous studies have indicated, questions about anxiety related to health measure not only health itself but also expectations.33 Anxiety about health among working women may derive from their jobs in that they may be unsure about whether they can survive in a work situation, a factor that was not a problem for housewives. According to a previous longitudinal study, the health status of female workers in Japan with both regular and fixed-term employment deteriorated after 2004. An a posteriori hypothesis suggested that the increase in precarious non-regular work may have been the main cause of the deterioration in workers’ health.34 The working conditions of non-regular workers are known to be very poor compared with those of regular workers in terms of salary and welfare systems,26 and opportunities to be a full-time regular worker are very limited. Indeed, it is often the case that only new graduates became regular workers.35 The system governing the labour market and working conditions may contribute to workers’ demands to maintain and improve their health.

We found a significant difference between housewives and working women without family demands in terms of demographic characteristics, especially among younger members of the latter group. Our data indicated that many younger workers did not marry and devoted themselves to regular paid work. In the context of the aforementioned labour market and working conditions, many Japanese women face a choice between a career and marriage. This situation may support the aforementioned assumption that workers feel unsure about whether they can survive in the work environment.

Despite the indication that housewives were significantly less satisfied with their present work status than were working women, they did not participate in the labour market. When asked in the survey why they chose their present status, 15% of housewives (n=36) answered that they retired from work because of their own health problems (data not shown). We conducted an additional analysis excluding those housewives who had retired for health reasons and found that the risk for poor health was higher among working women. This result indicates that housewives who had retired for health reasons were in poorer health than were housewives in general. Although housewives had better health during the survey period than did working women, they may have had poorer health in the past, when they were working. Consequently, in Japan, employment may not contribute to improving the health of working women and may, as a result, render healthy women reluctant to re-enter the work force.

In previous studies in which working women were found to have better health than unemployed housewives, researchers described several limitations of their conclusions. Although healthy female workers have been identified, poor health status has also been reported among the younger generation suffering from the burden of the multiple roles of housewife, mother and employee.36 Our finding that working women with family demands were in poorer health could be explained by these multiple roles. Although this finding cannot explain why working women without family demands were also in poorer health, the difficult working conditions in Japan may explain the poorer health of the younger generation. Furthermore, the lack of a protective effect of having children in the home could explain the health discrepancy. Marriage and parenthood mediate poor mental health among the unemployed,19 and this effect could be associated with our finding of better health in housewives.

The excess mortality among single working mothers has been associated with the absence of support from a marital partner.22 More than half of Japanese working women are in precarious work positions,25 and such working conditions are not especially positive from a financial perspective.26 Moreover, male Japanese workers with family demands tend not to devote time to their domestic situations. Indeed, male workers work longer hours than do female workers, and more than half of men participate in leisure activities and regular drinking sessions more frequently than do women.18 In addition to the lack of childcare, we think that Japanese working women, similar to single mothers, may suffer from the burdens associated with holding multiple roles related to work and home. Thus, it is not surprising that we found no healthy-worker effect among working women.

Although the job assistance available to working women is inadequate, several systems support housewives in Japan. For example, Japan has had a universal public pension and health insurance system since 1961, and all citizens must participate in these systems. Japan's pension system provides full-time housewives with various privileges under certain conditions.37 If a citizen's spouse is a salaried worker and the citizen's annual income is less than 1 300 000 yen (GBP10 000 based on a 130 yen/pound exchange rate), the citizen qualifies for a national pension without paying premiums. The health insurance system is based on the same principle, and salaried workers married to low-income citizens reap some benefits in terms of tax exemptions. In the context of the sex gap characterising earning37 and participation in economic activities,23 this spousal support system is utilised primarily by women. Additionally, housewives who are divorced or widowed are granted privileges in their tax and social welfare allowances. Indeed, the conditions under which a widow can claim exemption differ by sex. Until 2009, allowances for dependent children were provided only to women in Japan. These aspects of the social environment may encourage healthy women to remain in the home and improve their health.

As a preliminary study, we analysed data from a nationally representative survey, the 2007 Comprehensive Survey of Living Conditions of the People on Health Welfare38 to assess the effect of employment status on the self-rated health of women in the cohort aged from 22 to 44 years. Subjects were divided into three groups according to job status and marital status: married subjects engaging in housework (n=2153), married subjects engaging in paid work (n=2989) and unmarried subjects engaging in paid work (n=408). We conducted similar multiple logistic regression analyses to estimate the risk for poor self-rated health. When married women engaging in housework were used as the reference group, the adjusted OR of poor self-rated health among married working women was 1.00 (95% CI 0.84 to 1.21) and that among unmarried working women was 0.96 (95% CI 0.77 to 1.12). We found no evidence that working women had a significantly better health status than did housewives, even when income levels were subjected to greater control (upper 25% or lower 75%) to test the effect of socioeconomic status, which was used to approximate educational background. Although the definitions of the groups used in the preliminary study were not identical to those used in the present research, our study is consistent with these national data in terms of the health of working women in Japan.

This study has several limitations. First, all variables were measured by self-reporting. Objective measures of health status, such as biochemical examinations and physiochemical studies, would be more appropriate for inclusion in evidence-based assessments of health status. It may be feasible to use objective measures to study individuals who belong to a particular health-related group, such as hospital patients, disease or accident survivors, and students in a maternity or parenting class, by visiting the appropriate venue. According to other questionnaire-based research that relied on mailed surveys or interviews, the observed result should be interpreted as in the range of subjective health status.

Second, all participants were adult women who had graduated from a university, which may have affected the generalisability of the results because such people often come from higher-income families.23 However, the university in question was a national university located in a metropolitan area, and the tuition at this institution was lower than that in private universities. A report issued by the Japan Association of National Universities indicated that more students with lower income levels attend national than private universities and that national universities can mitigate regional economic disparities between metropolitan and rural areas.39 Metropolitan areas tend to attract more than the national average of individuals aged approximately 20 years, probably due the educational and employment opportunities available in such places.40 Therefore, students are expected to come to these areas from a variety of locations around the country. Thus, it is reasonable to assume that participants were drawn from a variety of socioeconomic backgrounds. Additionally, according to a 2007 national survey,24 the number of female university graduates has increased in recent decades, from 13.8% among women now in their early 40s to 26.9% among those now in their late 20s. Based on these findings and the study limitations, our results can be generalised as representative of well-educated women, a group whose numbers are expected to increase in the future.

We recruited study participants by asking for voluntary participation, and 16.5% of candidate subjects showed a willingness to participate. Moreover, the final response rate was 15.4%. We propose two reasons for such a low response rate. First, it is possible that some potential participants lacked confidence. This survey, which was conducted with the cooperation of the alumnae association, was the first experience available to this group via this channel. Indeed, the alumnae association had never released contact information for the purpose of a particular study. Owing to the increased emphasis in Japan on the protection of personal information, many people have become very sensitive about the use of their private address, even for a purpose related to public welfare. This has been particularly so since the Personal Information Protection law went into effect in April 2005, which was just before this survey was conducted. Many potential respondents may have reacted with suspicion to our mailed solicitation of participation. In fact, the alumnae association received a number of inquiries to confirm that this survey was endorsed by the association. This would indicate that many potential participants were sceptical and did not take action.

The complexity of the study design may have been another reason for the low response rate. The survey was implemented in two phases, recruitment and participation. The complexity of the procedure may have operated synergistically with the aforementioned lack of confidence, in that potential respondents were unable to obtain more detailed information about our study, including the actual questionnaire, until they received the second mailing. Moreover, transfer students were unable to participate owing to the two-phase procedure, because the school and fiscal years in Japan begin in April. The effect of not updating contact information on the low response rate remains unknown, but can be estimated as very small because the alumnae association frequently uses this contact information to send alumnae bulletins at regular intervals.

Thus, from the perspective of selection bias, study participants may have held positive attitudes towards public health and related research and maintained relatively stable lifestyles. The effect of the former tendency is ambiguous, but the latter tendency may have improved the accuracy of our findings given that life transition was a confounding factor.

We recruited study participants by providing limited information about the study purpose and used several key words, employment status and health, in our recruitment efforts. This approach may have selectively included those who were interested in employment status and/or health. Study participants might be more health conscious than those who did not participate, and their health behaviours might, therefore, be better than those of women of the same age in the general population. Additionally, study participants may have been more worried about their health status as it relates to their job than were those who did not participate (eg, participants who retired because of health problems or those who were suffering from health problems caused by employment-related stress). As a result, the study participants may have had poorer health status than the general female population of the same age. However, such self-selection bias could work in both directions, and it would not be evident which effect was stronger.

Classification errors were unlikely because we divided the participants into housewives and two categories of working women based on objective conditions, such as asking about employment status, marital status and living with family members. Although our study design was not longitudinal or interventional, we were able to obtain a sufficient sample size with relatively few missing data.