Education, Social Roles, and the Risk of Cardiovascular Disease Among Middle-Aged Japanese Women
The JPHC Study Cohort I
Background and Purpose— Little research has been conducted into variations in women’s health in relation to educational level and social roles in Japan. We sought to examine the effect of educational level on risk of cardiovascular disease and its modification by social roles at work and at home under the Japan Public Health Center-based Prospective Study (JPHC Study) Cohort I.
Methods— We calculated the adjusted hazard ratios of educational level for cardiovascular disease incidence within a 12-year study of 20 543 Japanese women aged 40 to 59 without history of stroke or heart disease.
Results— The respective age and area-adjusted hazard ratios for junior high school education and college or higher education compared to high school education were 1.63 (95% CI: 1.29, 2.06) and 1.41(95% CI: 0.96, 2.05) for total stroke, 2.20 (95% CI: 1.34, 3.60) and 2.20 (95% CI: 1.08, 4.48) for subarachnoid hemorrhage, and 1.90 (95% CI: 1.30, 2.76) and 1.60 (95% CI: 0.87, 2.93) for ischemic stroke. The U-shaped association with risk of total stroke was primarily observed for working women with single social roles at home. No association was found between educational level and risk of coronary heart disease or intraparenchymal hemorrhage.
Conclusions— A potential benefit of multiple social roles was suggested for stroke risk reduction among highly educated working women.
Lower educational levels have been associated with the incidence of coronary heart disease and stroke among women in Europe and the United States,1,2 but as far as we know, no studies have been conducted to examine associations between educational level and the incidence of cardiovascular disease among women in Asia. Moreover, no prospective studies in either Asian or Western countries have examined the effect modification of social roles at work (eg, paid employment) and social roles in the household (eg, parent, child, or partner) on associations between educational level and cardiovascular disease.3 We hypothesized an inverse association between educational level and risks of stroke or coronary heart disease, and that association was modified by social role.
Materials and Methods
We used data from the Japan Public Health Center-Based Prospective Study (JPHC Study) Cohort I, a large population-based prospec-tive study of 27 389 women aged 40 to 59.4 The baseline self-administered questionnaire was distributed to all registered participants in 1990, and the response rate was 82.1%. Participants who reported history of physician-diagnosed cancer, stroke, or myocardial infarction at baseline (n=883) and did not provide information on educational level (n=696) as well as those who reported “others” as their educational level (n=362) were excluded. The remaining 20 543 female participants constituted our study population.
The study was approved by the human ethics review committee of the National Cancer Center.
Educational level was categorized into 3 groups: (0) junior high school education, (1) high school education, and (2) any college or higher education by reported highest academic background at baseline. Subjects reported perceived psychological stress (low, moderate, high) and current employment status (no job or working). Social role in the household was identified by the number of categories of family members (eg, partner, parent, child, and other) living together at baseline: (0) no(living alone), (1) single, and (2) multiple. Cardiovascular events (stroke, stroke subtypes, and coronary heart disease) were registered if they occurred between the date of return of the baseline questionnaire and December 31, 2002. Coronary heat disease was defined as acute myocardial infarction and sudden cardiac death within 1 hour of the onset. At each of 30 registered hospitals, medical records were reviewed by registered hospital workers or PHC physicians. Review of death certificates and the 10-year follow-up questionnaire was also conducted. The ascertainment methods and diagnostic criteria for stroke and coronary heart disease have been described in detail elsewhere.5
Differences in the proportions of selected characteristics of study subjects by educational level were assessed by χ2 test. We calculated the adjusted hazard ratios of stroke or coronary heart disease incidence according to educational level by the Cox proportional hazard regression analysis.
The mean age of the subjects was 49 years, and 55% reported junior high school as their highest level of schooling (Table 1).
There was a U-shaped association of educational level with risk of total stroke, more specifically subarachnoid hemorrhage (Table 2). We chose the high school education group as reference to obtain excess risk estimates for the lower and higher education groups. Women with junior high school education showed a higher incidence of total stroke, subarachnoid hemorrhage, and ischemic stroke and a higher incidence of subarachnoid hemorrhage than did high school graduates. Among nonworking women, only the lowest educational level was associated with increased risks of total stroke and ischemic stroke, whereas both lowest and highest educational levels were associated with increased risks of total stroke, more specifically subarachnoid hemorrhage among working women (Table 2). The interaction term between educational level and employment status on the risk of total stroke was statistically significant but not for subarachnoid hemorrhage (P=0.019, and P=0.16, respectively).
Working women were more likely to perceive high psychological stress than nonworking women (24% and 15%, respectively). Within working women, the proportion of high psychological stress was 19% in junior high school level, 26% in high school level, and 40% in college or higher level.
The significant U-shaped relationship between educational level and risk of stroke was apparent among working women with single social role in the household but not among those with multiple social roles (Table 3).
The picture obtained from this study was different from that of European countries and the United States, as we found no association between educational level and the risk of coronary heart disease but identified a U-shaped relationship between educational level and the risk of total stroke, particularly subarachnoid hemorrhage. This U-shaped relationship was confined to working women, in particular those with single social role in the household.
The higher prevalence of perceived psychological stress among working women with the higher educational level implies that psychological stress could be one of the plausible explanations for higher risk of stroke among working women with high educational level because perceived psychological stress was associated with an increased risk of death from stroke, in particular subarachnoid hemorrhage in a previous Japanese study.6 This mechanism is in line with role conflict/strain theory.7 The weak impact of adjustment for perceived psychological stress on the education-disease association may be attributable to the weak measurement of individual psychological stress in our study.
Our data indicated that multiple social roles in the household may act as a buffer against the effect of educational level on the risk of stroke among highly-educated working women. Working women, in particular with a high educational level, may derive psychological strength from their multiple social roles in the household to resist the adverse effect of psychological stress on health; this mechanism is in line with role enhancement theory.7 High risk of stroke among working women with single social role could be explained by their higher smoking prevalence and heavy drinking (not shown in the table). They could obtain poorer health behaviors as their stress coping strategy,8 which increased their risk of stroke.
There was a U-shaped association between educational level, and risk of stroke was identified among Japanese women, particularly working women. The excess risk of stroke in the highest education group was primarily observed among working women with single social role in the household. Our findings suggest potential benefit of multiple social roles for stroke risk reduction among highly-educated working women.
The authors thank Professor Ichiro Kawachi, Harvard school of public health for his valuable comments and all staff members in each of the study areas and in the central office for their extensive efforts to conduct the baseline survey and follow-up.
Members of the Japan Public Health Center-based Prospective Study (JPHC Study; principal investigator: S. Tsugane) Group are: S. Tsugane, M. Inoue, T. Sobue, and T. Hanaoka, Research Center for Cancer Prevention and Screening, National Cancer Center, Tokyo; J. Ogata, S. Baba, T. Mannami, and A. Okayama, National Cardiovascular Center, Suita; K. Miyakawa, F. Saito, A. Koizumi, Y. Sano, and I. Hashimoto, Iwate Prefectural Ninohe Public Health Center, Ninohe; Y. Miyajima, N. Suzuki, S. Nagasawa, and Y. Furusugi, Akita Prefectural Yokote Public Health Center, Yokote; H. Sanada, Y. Hatayama, F. Kobayashi, H. Uchino, Y. Shirai, T. Kondo, R. Sasaki, Y. Watanabe, and Y. Miyagawa, Nagano Prefectural Saku Public Health Center, Saku; Y. Kishimoto, E. Takara, T. Fukuyama, M. Kinjo, M. Irei, and H. Sakiyama, Okinawa Prefectural Chubu Public Health Center, Okinawa; K. Imoto, H. Yazawa, T. Seo, A. Seiko, F. Ito, and F. Shoji, Katsushika Public Health Center, Tokyo; A. Murata, K. Minato, K. Motegi, and T. Fujieda, Ibaraki Prefectural Mito Public Health Center, Mito; K. Matsui, T. Abe, M. Katagiri, and M. Suzuki, Niigata Prefectural Kashiwazaki and Nagaoka Public Health Center, Kashiwazaki and Nagaoka; M. Doi, A. Terao, and Y. Ishikawa, Kochi Prefectural Chuo-higashi Public Health Center, Tosayamada; H. Sueta, H. Doi, M. Urata, N. Okamoto, and F. Ide, Nagasaki Prefectural Kamigoto Public Health Center, Arikawa; H. Sakiyama, N. Onga, and H. Takaesu, Okinawa Prefectural Miyako Public Health Center, Hirara; F. Horii, I. Asano, H. Yamaguchi, K. Aoki, S. Maruyama, and M. Ichii, Osaka Prefectural Suita Public Health Center, Suita; S. Matsushima and S. Natsukawa, Saku General Hospital, Usuda; M. Akabane, Tokyo University of Agriculture, Tokyo; M. Konishi, and K. Okada, Ehime University, Ehime; H. Iso, Osaka University, Suita; Y. Honda and K. Yamagishi, Tsukuba University, Tsukuba; H. Sugimura, Hamamatsu University, Hamamatsu; Y. Tsubono, Tohoku University, Sendai; M. Kabuto, National Institute for Environmental Studies, Tsukuba; S. Tominaga, Aichi Cancer Center Research Institute, Nagoya; M. Iida and W. Ajiki, Osaka Medical Center for Cancer and Cardiovascular Disease, Osaka; S. Sato, Osaka Medical Center for Health Science and Promotion, Osaka; N. Yasuda, Kochi University, Nankoku; S. Kono, Kyushu University, Fukuoka; K. Suzuki, Research Institute for Brain and Blood Vessels Akita, Akita; Y. Takashima, Kyorin University, Mitaka; E. Maruyama, Kobe University, Kobe; M. Yamaguchi, Y. Matsumura, S. Sasaki, and S. Watanabe, National Institute of Health and Nutrition, Tokyo; T. Kadowaki, Tokyo University, Tokyo; Y. Kawaguchi, Tokyo Medical and Dental University, Tokyo; and H. Shimizu, Sakihae Institute, Gifu.
Sources of Funding
Funding of this work was provided by grants-in-aid for cancer research and for the Third-Term Comprehensive Ten-Year Strategy for Cancer Control from the Ministry of Health, Labor and Welfare of Japan.
Reprint requests to Shoichiro Tsugane, MD, Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan. E-mail email@example.com
- Received January 3, 2008.
- Revision received February 4, 2008.
- Accepted February 19, 2008.
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