Job strain has consistently been shown to be a risk factor for cardiovascular disease (CVD), and for blood pressure when it is measured with an ambulatory monitor (1). Job strain is defined as work that combines high psychological workload demands with low decision latitude or low control (2). In addition, some studies have suggested that the effect of job strain on CVD and on CVD risk factors is greater among men with lower socioeconomic status (SES), e.g., (3, 4). We tested this hypothesis in a sample of 283 healthy male employees, aged 30-60 at initial recruitment, at 8 New York City work sites, 195 of whom were restudied 3 years after their initial participation. Mean systolic (SAmBP) and diastolic (DAmBP) ambulatory blood pressure at work, home and during sleep were computed from 24-hour recordings and diary entries specifying location. Job characteristics were assessed by a psychosocial questionnaire. Multiple regression analysis was used to examine the cross-sectional and prospective associations of AmBP with job strain, controlling for age, body mass, race/ethnicity, smoking, alcohol consumption, and worksite. Interaction terms were computed by multiplying job strain by years of education, occupational status (Nam-Powers scale, which ranges from 1-99), occupational category (white-collar; clerical, technical or adminstrative; blue-collar) and personal or family income.

Initial study results had indicated a substantial association between job strain and AmBP both cross-sectionally (5, 6) and prospectively (7). We now find that the job strain-AmBP association at entry into the study (Time 1) was somewhat stronger among men with lower SES. For example, compared to men with a college degree and without job strain, the work SAmBP of men with only a high school degree or less and with job strain was 7.2 mm Hg higher, but the work SAmBP of college graduates with job strain was only 2.6 mm Hg higher. Similarly, compared to white-collar workers without job strain, the work SAmBP of blue-collar workers with job strain was 12.5 mm Hg higher, but the work SAmBP of white-collar workers with job strain was only 3.4 mm Hg higher. In addition, the observed fall in AmBP over 3 years among men leaving job strain was somewhat greater for those with lower SES. For example, among men who entered the study exposed to job strain but were not exposed three years later, those with family income below the median ($55,000) showed a decrease of 5.5 mm Hg work DAmBP, while those with higher incomes had virtually no change in work DAmBP. Similar findings were observed for home and sleep AmBP.
In summary, men with lower SES show a greater impact of job strain on blood pressure and a greater benefit when leaving a situation of job strain. SES had no consistent main effect on blood pressure. Overall, the main predictors of blood pressure in this sample are age, race, body mass index (BMI) and job strain. The main predictors of blood pressure change are BMI change and job strain change (7).

References

1. Schnall, P.L., P.A. Landsbergis & D. Baker. 1994. Job strain and cardiovascular disease. Annu Rev Public Health 15: 381-411
2. Karasek, R. & T. Theorell. 1990. Healthy work: stress, productivity, and the reconstruction of working life.
3. Johnson, J.V., E.M. Hall & T. Theorell. 1989. Combined effects of job strain and social isolation on cardiovascular disease morbidity and mortality in a random sample of the Swedish male working population. Scand J Work Environ Health 15: 271-9
4. Hallqvist, J., F. Diderichsen, T. Theorell, C. Reuterwall, A. Ahlbom & The SHEEP Study Group. 1998. Is the effect of job strain on myocardial infarction due to interaction between high psychological demands and low decision latitude? Results from Stockholm Heart Epidemiology Program (SHEEP). Soc Sci Med 46: 1405-1415
5. Schnall, P.L., J.E. Schwartz, P.A. Landsbergis, K. Warren & T.G. Pickering. 1992. Relation between job strain, alcohol, and ambulatory blood pressure. Hypertension 19: 488-94
6. Landsbergis, P.A., P.L. Schnall, K. Warren, T. G. Pickering & J. E. Schwartz. 1994. Association between ambulatory blood pressure and alternative formulations of job strain. Scand J Work Environ Health 20: 349-63
7. Schnall, P.L., P.A. Landsbergis, J. Schwartz, K. Warren & T.G. Pickering. 1998. A longitudinal study of job strain and ambulatory blood pressure: Results from a three-year follow-up. Psychosom Med 60: 697-706.