Occup Environ Med 2001;58:367–373 367 Occup Environ Med: first published as 10.1136/oem.58.6.367 on 1 June 2001. Downloaded from Association between job strain and prevalence of hypertension: a cross sectional analysis in a Japanese working population with a wide range of occupations: the Jichi Medical School cohort study A Tsutsumi, K Kayaba, K Tsutsumi, M Igarashi, on behalf of the Jichi Medical School Cohort Study Group Abstract Keywords: hypertension; stress; psychological; work Objectives—To explore the association between the prevalence of hypertension in a Japanese working population and job Comprehensive reviews conclude that job strain (a combination of low control over strain, a combination of low control over the work and high psychological demands), job and high psychological demands, is related to the incidence and prevalence of cardiovas- and to estimate this association in diVer- 1–3 ent sociodemographic strata. cular diseases in western countries. It was Methods—From a multicentre commu- postulated that one of the underlying mecha- nisms through which job strain leads to cardio- nity based cohort study of Japanese peo- vascular diseases is high blood pressure due to ple, sex specific cross sectional analyses chronic physiological arousal.2 Several studies were performed on 3187 men and 3400 have been conducted to substantiate this women under 65 years of age, all of whom hypothesis; and evidence has been accumulat- were actively engaged in various occupa- ing to prove a cause-eVect relation between job tions throughout Japan. The baseline strain and high blood pressure.4–8 However, the period was 1992–4. The association be- results have not been completely consistent.9–13 tween job characteristics—measured with Also, cross cultural evidence has been very lim- a Japanese version of the Karasek ited.2 demand-control questionnaire—and the It might be expected that a clearer associ- prevalence of hypertension defined by ation between job strain and hypertension blood pressure and from clinical diag- would emerge in some social strata. Occupa- noses were examined. Adjustments were tional class and educational level are variables made for possible confounders. The to be taken into consideration.14 Low occupa- analyses were repeated for stratified cat- tional class has often been reported to be egories of occupational class, educational associated with high blood pressure.15 16 Other http://oem.bmj.com/ attainment, and age group. levels of social class and education may also Results—In men, the level of job strain determine levels of blood pressure independ- (the ratio of psychological job demands to ently or together from work conditions.9 Many job control) correlated with the preva- researchers have controlled for these variables, lence of hypertension. In a multiple logis- if taken into account, in their statistical tic regression model, job strain was analyses, but a stratified analysis has seldom significantly related to hypertension been done. Furthermore, a sex diVerence (odds ratio 1.18; 95% confidence interval seems to exist in the association between job on September 29, 2021 by guest. Protected copyright. 1.05 to 1.32), after adjustment for age, strain and blood pressure. Light et al17 and employment (white collar v blue collar), Niedhammer et al18 (not job strain, but job Department of marital status, family history of hyper- control) reported a positive association in men Environmental tension, cigarette smoking, alcohol in- but not in women, whereas positive associa- Medicine, Kurume take, physical activity, and body mass 19 20 University School of tions in women were found by others. Age Medicine, Japan index. The stratified analyses showed sig- diVerences have also been suggested. The A Tsutsumi nificant excess risks in the subordinate eVect that job strain has on blood pressure groups compared with managers, blue seems to be more likely in the older age Department of collar workers, less educated workers, groups.611Sampling from a diverse population Community and and the older age groups. This association would be appropriate to determine in which Family Medicine, Jichi Medical School, Japan was not significant in women. Multiple populations the most prominent eVects of job K Kayaba linear regression analyses, with systolic strain will emerge. M Igarashi and diastolic blood pressures as depend- The Jichi Medical School cohort study, a ent variables, did not show any significant multicentre community based cohort study, Faculty of Economics, association. which is designed to explore coronary risk fac- Kyushu International Conclusions—The findings provided lim- tors in the Japanese people, provides the tools University, Japan K Tsutsumi ited proof that job strain is related to to examine whether job strain is associated with hypertension in Japanese working men. the prevalence of hypertension among male Correspondence to: Older men in a lower social class may be and female Japanese workers across various Dr A Tsutsumi more vulnerable to the hypertensive ef- occupations. This was tested for some socio- [email protected] fects of job strain. demographic categories in non-western occu- Accepted 1 February 2001 (Occup Environ Med 2001;58:367–373) pational settings. www.occenvmed.com 368 Tsutsumi, Kayaba, Tsutsumi, et al Occup Environ Med: first published as 10.1136/oem.58.6.367 on 1 June 2001. Downloaded from Methods to do work, and conflicting demands). Job con- The aim of the Jichi Medical School cohort trol was defined as the sum of two subscales study was to investigate the risk factors for that were given equal weight: (a) skill discre- cardiovascular disease in Japan. Data were col- tion, measured by four elements (continuous lected between 1992 and 1994. Ultimately, need to acquire new knowledge, skill require- 12 490 Japanese workers from 12 rural com- ment, requirement for creativity, and repeti- munities across Japan participated.21 22 In Japan tiveness); and (b) decision authority, measured in accordance with the Health and Medical by two elements (freedom to make decisions Service Law for the Aged, mass screening and choice in the approach to work). The psy- examinations for cardiocerebrovascular dis- chometric property of the Japanese version of eases have been conducted since 1983. The the demand-control questionnaire has been subjects for these examinations were residents reported elsewhere.23 24 All questions were with ages between 30 and 69 years in four of scored on a Likert scale of 1 to 4. Cronbach’s the 12 communities and between 40 and 69 coeYcient á for the psychological demands years in the other eight. In each community, the index was 0.70 and for the job control index it local government oYce sent letters to all was 0.64 for our sample. Job strain was defined potential participants inviting them to take part as the ratio of demands to job control. Partici- in the programme. The invitation mentioned pants were grouped into one of three strata for that people who were visiting hospitals or clin- each job characteristics index (low, medium, or ics because of cardiovascular diseases did not high) based on tertiles, defined according to have to take the examination. The overall the distribution of scores in the total working response rate was 65.4%. People other than population, and separately for men and those involved in these age groups (n=282 for women. the younger age group and 699 for those over The following variables were selected as 69), who voluntarily participated in the study potential confounders: (a) age, <35, 36–45, were included in the database. The final 46–55, and 56–65; (b) job, managerial (self database comprised 4911 men and 7579 employed or a manager in their company) or women. not, and employment of white collar versus blue collar; (c) work hours, the number of PROCEDURE hours spent at work on any given weekday; (d) Sociodemographic and behavioural variables marital status, currently married or single; (e) were investigated through a standardised ques- educational attainment, lower or higher than tionnaire, which requested information on age, the level of compulsory education; (f) family occupational environment, marital status, edu- history of hypertension, positive if participant’s cation, family medical history, smoking, alco- mother or father had ever had high blood pres- hol consumption, and physical activity. The sure; (g) smoking habits, never smoked, questionnaire was given to the participants to ex-smoker, 1–20 cigarettes/day, or >21 complete on their own before the physical cigarettes/day for men, and never smoked, examination. Informed consent was obtained ex-smoker, or current smoker for women; (h) http://oem.bmj.com/ from all prospective participants. alcohol intake, non-drinker, <1 go daily (go=a The physical examinations took place in traditional Japanese alcohol unit, 1 go=28.9 g each community. Height was measured with- alcohol), 1–3 go daily (28.9–86.6 g alcohol), or out shoes. Body weight was recorded with the >3 go daily (>86.7 g alcohol) for men, and subject clothed, and 0.5 kg in summer or 1 kg non-drinker or current drinker for women; (i) in the other seasons was subtracted from the physical activity index,25 low (<28), medium recorded weight. Body mass index was calcu- (29–36), or high (>37); and (j) body mass lated as weight (kg)/height (m)2. The systolic index, categorised into tertiles based on the and diastolic blood pressures were measured total sample distribution (<21.6, 21.6–23.9, or on September 29, 2021 by guest. Protected copyright. with a fully automated sphygmomanometer >24.0 kg/m2). (BP203RV-II, Nippon Colin, Komaki, Japan), which was placed on the right arm of the sub- STUDY POPULATION ject, after he or she had been sitting for 5 min- The study population was restricted to actively utes. People were classified as hypertensive if working men and women under 65 because the (a) their systolic blood pressure was equal to or aim of this analysis was to find the association greater than 160 mm Hg, (b) their diastolic between job characteristics and the prevalence blood pressure was equal to or greater than 90 of hypertension.