Job Stress and Strain and Blood Pressure

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An extensive amount of research has been conducted in work settings exploring the relation between blood pressure and either job stress or job strain (see Pickering, 1997, for a review). Many of the studies ex ploring the relation between job stress and hypertension have been based upon the Job Strain Model proposed by Karasek and colleagues (Karasek, 1979; Karasek et al., 1981). According to this perspective, job strain is influenced jointly by the psychological demands of the job andthe degree to which the employee controls or makes decisions regarding work outcome. Jobs that involve considerable psychological demands on the worker accompanied by very little control are characterized as having high job strain (Karasek, 1979). Interestingly, Karasek chose to use the term 'strain' to refer to these stimulus characteristics of an individual's job. To remain true to the original usage of stress and strain in physics, Selye (1956) should have probably used the term 'strain' to discuss the physiological response components to stress and Karasek should have probably used the term 'stress' to refer to the stimulus characteristics of the job. Regardless of his choice of terms, Karasek hypothesized that workers in positions with high job strain would be expected to exhibit higher rates of a variety of stress-related diseases including coronary heart disease and essential hypertension. Let's examine the evidence for this perspective.

Studies Relating Job Stress/Strain to Prevalence of Hypertension Several studies examining the relations between job stress and hypertension have focused on comparing prevalence rates of diagnoses of hypertension among various jobs categorized as being more or less stressful. In these studies, a participant's blood pressures are typically measured during a medical examination or diagnosis is confirmed through a review of the participant's medical records. Although many of these studies employ standardized measures of job strain, a la Karasek (1979), others rely on less objective methods for defining job stress. For example, Cobb and Rose (1973) conducted one of the earlier studies examining the relation between job stress associated with being an air traffic controller and hypertension. In this study, the investigators chose to examine what they considered a single high-stress position, that of air traffic controller, based upon the knowledge that persons in this occupational category experience grave consequences for any mistake that might be made. They compared the air traffic controllers with a group of second-class airmen, who were judged to experience considerably less stress on the job. Not only did they report that the prevalence of hypertension was higher among air traffic controllers than second-class airmen, but also that the rates of hypertension increased among air traffic controllers in proportion to the density of air traffic at their work location. Associations between a stressful job environment and increased rate of hypertension have been observed in many other samples as well, including blue-collar factory workers (Matthews et al., 1987), pregnant women with high-status jobs (Lands-bergis and Hatch, 1996), transit vehicle operators (Ragland et al., 1997), and workers in electrical factories (Kawakami, Haratini, and Araki, 1998).

Pieper, LaCroix, and Karasek (1989) conducted an extensive analysis of the relation between job stress and cardiovascular risk factors, including hypertension, using data from five major investigations, including the Western Collaborative Group Study, the Exercise Heart Study, the National Health Examination Survey, and both the first and second reports of the National Health and Nutrition Examination Surveys. As in the Karasek (1979) model, job stress was conceptualized as involving both psychologic demands on the worker and job control. Psychologic demands were based upon ratings of working hard and fast, confronting conflicting demands, and not having enough time to complete job-related assignments. Job decision latitude (or job control) was defined by participants' responses to questions regarding their ability to learn new skills on the job, have a variety of work assignments, and be involved in decision-making on the job. Although there was no association between job decision latitude and DBP, there was a relation observed between job decision latitude and SBP in three of the five data bases. In these large-scale data sets, higher job decision latitude (greater job control) was associated with lower SBP. Unusually, higher psychologic demands of the job were associated with increased SBP in only one data base, but inversely correlated with both SBP and DBP in the Western Collaborative Group Study. In other words, excessive work with conflicting demands was unexpectedly associated with lower blood pressure in the Western Collaborative Group Study sample. Although these findings may be attributed to the uniqueness of the executive men that comprised the Western Collaborative Study group, the general lack of evidence for a relation between job demands and blood pressure among the other large-scale samples suggested that job control may be a more important predictor of blood pressure status than job demands.

Using Karasek's (1979) job strain measure, Schnall et al. (1990) found that hypertensive urban employees were almost three times more likely to have high job strain than normotensive employees. Further, hypertensive patients with high job strain exhibited greater left ventricular hypertrophy (hypertensive target organ damage) than hypertensive patients with low job strain. Not only was a strong association between job strain and hypertension reported among patients with high job strain, but also evidence of actual tissue damage to the heart. In a similar study, Cesana et al. (2003) recently examined the relation between job strain measured using Karasek's categorization system and clinic measures of blood pressure and found that high job strain was linked to increased SBP in men; there was no effect for DBP however, nor did the findings extend to women. In direct contrast to these findings, Alfredsson et al. (2002) found job strain to be associated with an increased prevalence of hypertension among women, but not men. Finally, Markovitz et al. (2004) reported that increased job strain during an eight-year data collection period was predictive of onset of essential hypertension. In this study, persons who changed from low-strain to high-strain jobs exhibited a higher incidence of high blood pressure, even more than persons who had high-strain jobs throughout the entire period.

Not all studies that have examined the relation between job stress or job strain and prevalence of hypertension have revealed significant associations. Albright et al. (1992) found an inverse relation between job stress and prevalence of hypertension among bus drivers, and Tarumi, Hagihara, and Morimoto (1993) found a similar inverse relation among white-collar workers in Japan. Employment, even in stressful jobs, has also been shown to be inversely associated with levels of blood pressure in women (Rose et al., 1999; Weidner et al., 1997). In a few other reports, no association between job stress and hypertension was reported among female nurses (Riese et al., 2000) or within a community of African American men and women (Curtis et al., 1997).

To further complicate these mixed findings, several researchers have found that the linkage between job stress or job strain and high blood pressure is affected by individual difference variables. For exam ple, Chesney et al. (1981) found the expected association between both worker autonomy and peer support and lower blood pressure, but only among workers with a Type A behavior pattern. Likewise, job dissatisfaction has been shown to be associated with hypertension, but only among men who suppress anger (Cottington et al., 1986). In a more recent investigation, although no direct relation was observed between work-related stress and blood pressure among government tax office workers, there was support for an indirect association between stress and blood pressure that was explained by coping strategies (Lindquist, Beilin, and Knuiman, 1997). Specifically, persons who engaged in less adaptive coping, which included those who drank alcohol, engaged in binge eating, and were physically inactive, responded to stress with increased blood pressures. Comparable relations between stress and blood pressure were not observed among workers who exhibited more adaptive means of coping with stress. The empirical work to date makes it quite clear that the association between job stress or strain and hypertensive status, as measured by either clinic records or clinic measures of blood pressure, is not a simple and straightforward one.

Studies Relating Job Stress/Strain to Ambulatory Measures of Blood Pressure

With the advent of ambulatory blood pressure monitoring technology, there was considerable interest in extending the understanding of the relation between job stress/strain and blood pressure by measuring blood pressure while the worker was actually on the job. As described in Chapter 2, measures of blood pressure obtained in the clinic may either overestimate or underestimate actual daily blood pressures; thus, ambulatory measures of blood pressure are thought to provide a more accurate depiction of a patient's daily blood pressure profile. In one of the earlier studies to use ambulatory blood pressure monitoring on the job, Theorell et al. (1991) reported that job strain, as defined by Karasek's classification model (1979), was associated with higher DBPs among borderline hypertensive men both at work and at night (during sleep). No relation, however, was observed between job strain and SBP.

Based upon observations that hypertensive patients from several work sites in New York City were more likely to have positions with high job strain than normal blood pressure controls, the Cornell Work

Site Blood Pressure Study, devised as a prospective study of the relation between job strain and hypertension, began in 1985. Ambulatory measures of blood pressure from participants in this large-scale study revealed that job strain was associated with a 6.8 mm Hg increase in daily SBP and a 2.8 mm Hg in daily DBP (Schnall et al., 1992). As in the study by Theorell and colleagues, the observed blood pressure differences associated with job strain were also evident at home and during periods of sleep. Three-year follow-up data confirmed the chronic nature of this association (Schnall et al., 1998). Workers who were in high job strain positions maintained higher ambulatory blood pressures after three years than those in low job strain positions. Interestingly, ambulatory blood pressures decreased among workers who reported highstrain jobs during the initial evaluation and low-strain jobs three years later. The opposite effect, however, was not observed among workers who initially reported having a position with low job strain and reported a high-strain job at follow-up. The authors speculated that perhaps a period longer than three years was needed for individuals who recently assumed a high-strain job to develop hypertension. To support this hypothesis, a subsequent analysis was conducted on lifetime job history and blood pressure status at the follow-up visit. Results confirmed that workers who spent the majority of their working life in high job strain positions, defined as having a high 'cumulative burden' of job strain, evidenced significant blood pressure elevations in contrast to those workers who spent fewer years in such positions (Landsbergis et al., 2003a). Recent empirical work has confirmed the associations between job strain and ambulatory blood pressures among workers in other industrialized countries (Cesana et al., 1996; Melamed et al., 1998).

In a comprehensive study addressing the relation between job strain, as assessed using the Karasek model, on nurses, Fox, Dwyer, and Ganster (1993) obtained measures of both subjective job strain (from nurse self-reports) and objective job demands (from ratings of patient load, number of deaths witnessed, and percentage of patient contact as determined by nursing supervisor ratings). Although subjective measures of job strain were related to SBP and cortisol measured at work and both SBP and DBP at home, the univariate correlations between measures of job stress and blood pressure were higher for objective than subjective measures. These findings suggest that self-reported ratings of perceived job stress by women may be influenced by factors that may obscure actual associations between workload and blood pressure status factors (for example, the tendency to underreport symptoms of stress).

Like studies relating job stress/strain to hypertension or office blood pressure measures, findings from research linking job stress/ strain to ambulatory measures of blood pressure have revealed that numerous individual factors appear to influence the relation. Even the data from the Cornell Work Site Study showed that alcohol use interacted with high-strain jobs to raise SBP, but had no effect on SBPs among workers in low-strain jobs (Schnall et al., 1992). Furthermore, in another report from the Cornell group, associations between job strain and ambulatory blood pressures were stronger among workers with low socioeconomic status; the relation between job strain and blood pressure was much smaller among workers with higher socioeconomic status (Landsbergis et al., 2003b).

In several studies, the relation between job strain and blood pressure status typically observed among men was not seen for women (Light, Turner, and Hinderliter, 1992; Schnall et al., 1992); however, in one study a significant relation between job stress and SBP was observed among women, but not men (Blumenthal, Thyrum, and Siegel, 1995). Finally, one study reported no relation between job strain and blood pressure among samples of both men and women (Matthews et al., 2000). It has been suggested that one reason that many studies fail to detect a relation between job strain and blood pressure among women pertains to the restricted range in job strain that exists among jobs typically held by women. Many jobs held by a significant portion of women are categorized as being high in strain, including those of elementary school teachers, secretaries, and nurses. Gallo et al. (2004) recently reported that women in these lower-status occupations indeed exhibited higher SBP and HR during ambulatory monitoring than women in higher-status occupations.

It has also been hypothesized that the stress women experience is more likely due to their combined family and work responsibilities, rather than purely work-related job stress. To explore this hypothesis, Brisson et al. (1999) conducted a study relating job strain among white-collar women and ambulatory blood pressures. They found that among women with college degrees, the highest ambulatory blood pressures were observed in those with both high job strain and significant family responsibilities. James, Schlussel, and Pickering (1993) also examined job stress and ambulatory blood pressures in working women categorized into those who reported a more stressful work than home environment and those who reported a more stressful home than work environment. In this study, ambulatory SBP was higher at work among work-stressed women than home-stressed women. Furthermore, the increased SBPs were associated with a greater increase in sympathetic nervous system activity during daily life, as measured by change in catecholamine secretion. Finally, in a study comparing ambulatory blood pressures of men and women, Marco et al. (2000) found higher blood pressures among men during workdays versus non-workdays, but a different pattern among women. Women without children exhibited the same pattern as men; women with children, however, exhibited comparable blood pressures at home and at work or even higher blood pressures at home. The findings from these studies suggest that research examining relations between job stress and hypertension in samples of women needs to develop better ways of including measures of family job responsibilities as well as job responsibilities at work settings.

Additionally, the relation between job stress and ambulatory measures of blood pressure has been shown to be influenced by occupational status (Blumenthal et al., 1995; Light et al., 1995), marital status (Blumenthal et al., 1995), high-effort coping or John Henryism (Light et al., 1995), social support (Steptoe, 2000), and anger expression style and defensiveness (Shapiro et al., 1993). For example, Light et al. found that women with high-status occupations and traits of high-effort coping (the perception that achievement can be attained through hard work and personal effort) exhibited higher DBPs during the workday than women with lower job status or without high-effort coping traits. Furthermore, the relation between job stress and hypertension is less likely to be observed among participants who are married or who have strong positive social support networks (Blumenthal et al., 1995; Steptoe, 2000).

Marital Stress and Blood Pressure

Familiar with the convincing evidence linking job strain with ambulatory measures of blood pressure, several investigators began to employ ambulatory blood pressure measures to examine another type of stress commonly encountered in life—marital stress (Baker et al., 1999; 2000; Carels et al., 2000). Like studies of job strain and ambulatory blood pressures, these studies have uncovered comparable associations between marital stress and both ambulatory blood pressures and left ventricular hypertrophy. Extending this work into the domain of the marital relationship makes it appear that perhaps the observed associations between job strain and blood pressure may not be unique to the work environment.

Summary

One thing becomes quite apparent when one examines the studies that have explored the relation between job stress or job strain and essential hypertension: the association is not a simple one. It is quite evident that there is no direct linear relation between job stress and measures of blood pressure. Among studies that have examined the relation between job stress and hypertension by using standard methods for establishing a diagnosis of hypertension (clinic measures, chart reviews), no consistent association has been observed. Among studies employing ambulatory measures of blood pressure, the relation between job stress and elevated blood pressure has been observed fairly consistently. However, it is sometimes unclear whether the elevated blood pressures observed in these studies constitute a diagnosis of essential hypertension or simply elevated normal blood pressures. Both literatures have revealed a substantial number of variables that appear to influence the relation between job stress and hypertension, including gender, the presence of social support, occupational status, socioeconomic status, marital status, presence of coexistent family responsibilities, alcohol use, and other coping strategies. Clearly, not all persons employed in high-strain jobs exhibit elevated blood pressures. In some reports, persons employed in high-strain jobs actually exhibited lower blood pressures (Albright et al., 1992; Tarumi et al., 1993; Weidner et al., 1997).

There are also inconsistent findings regarding the particular mea surement of blood pressure that is related to job stress. Some studies report a relation between job stress and SBP, but not DBP (Blumenthal et al., 1995), and others report a relation between job stress and DBP, but not SBP (Light et al., 1995). Although most studies using ambulatory blood pressure measurements found an association with job strain when examining blood pressures measured during work hours, inconsistent findings emerge when they examined blood pressures measured at home or during sleep. Some studies report associations between job stress and blood pressure at night (Schnall et al., 1992; Theorell et al., 1991) whereas other studies fail to detect this association (Sega et al., 1998; Steptoe et al., 2003). These findings suggest that although job stress and strain may be related to elevated ambulatory arterial pressures, the relation may operate through different mechanisms among different samples of workers.

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