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The Concept of Work Stress

The Occupational Stress Model1) of NationalInstitute of Occupational Safety and Health(NIOSH) is shown in Fig. 1 to facilitate under-standing of the concept of work stress and itseffect.

Stressors that constantly affect our healthexist in all types of work. By interacting withpersonal factors or non-workplace factors, thesework-related stressors induce what are called

‘stress reactions’. There are various stress reac-tions, including psychological responses (de-pression and dissatisfaction at work), physio-logical responses (blood pressure elevation andincreased heart rate), and behavioral responses(overeating, overdrinking, smoking, drug use,sickness absence, and accidents). Since the re-sponses are usually acute and transient, healthcan be restored by taking breaks, resting, sleep,or other adequate approaches.

When exposed to a powerful stressor for a

This article is a revised English version of a paper originally published inthe Journal of the Japan Medical Association (Vol. 128, No. 6, 2002, pages 885–888).The Japanese text is a transcript of a lecture originally aired on May 28, 2002, by the Nihon ShortwaveBroadcasting Co., Ltd., in its regular program “Special Course in Medicine”.

Job Stress and Stroke andCoronary Heart DiseaseJMAJ 47(5): 222–226, 2004

Fumio KOBAYASHI

Professor, Department of Health and Psychosocial Medicine,School of Medicine, Aichi Medical University

Abstract: Repetitive or long-lasting effects of work stressors cause a type ofexhaustion referred to as “accumulated fatigue,” that may eventually cause ische-mic heart disease or stroke. Among the various work stressors to which peoplemay be exposed, long work hours combined with lack of sleep is a major risk factorin our society. Irregular work hours, shift work, frequent work-related trips, workingin a cold or noisy environment, and jet lag are also potent risk factors for workers.In addition, the chronic effects of psychological job strain, which can be concep-tualized by the job demand-control-support model, are related to cardiovasculardisease. In this model, high job demand and low work control accompanied by lowsocial support at work are the most harmful to health. However, the biomedicalmechanisms connecting psychological job strain to cardiovascular disease remainto be fully clarified.

Key words: Job stress; Cardiovascular disease; Long hour work; Job strain

� Karoshi (Death from Overwork)

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ical, and ergonomic factors in the workplace,and the third is related to the characteristics ofthe work that are associated with psychologicalstress.

In this paper, we shall only briefly refer tothe first and second categories and focus onthe third stressor, the characteristics of workthat are associated with psychological stress ormental strain, and their effects.

1. Stressors associated with type of workOne of the major work stressors associated

with stroke and coronary heart disease is longworking hours. The data in Japan show that therisk of acute myocardial infarction for maleworkers who work more than 11 hours a day(i.e., approximately 60 hours a month over time)is 2.44 higher than for those who work 7–9hours a day. Working more than 60 hours a weekalso increases the risk of cerebrovascular andcardiovascular disease.

The effect of long working hours is closelyassociated with lack of sleep. Lack of sleep isgenerally thought to increase the reactivity ofthe circulatory and sympathetic nervous sys-tems. High angina pectoris and myocardialinfarction morbidity among persons gettingless than 6 hours sleep a day and 2.08 timeshigher mortality from ischemic heart diseaseand cerebrovascular disease among those get-ting less than 4 hours sleep a day than 7 hourshave been reported in some studies.

The entire time spent in the workplace, in-cluding nap time, break time, and staying at the

long period, however, the stress responsesincrease and become excessive, making it dif-ficult to restore health. This condition is gener-ally called ‘accumulation of fatigue’, and whenit persists for a long time, irreversible changes,such as poor physical function and the develop-ment of vascular disease, may occur. It mayalso induce stroke and coronary heart diseasein combination with other factors.

Thus, from the standpoint of occupationalhealth, it is important to focus on high-risk,work-related stressors in order to investigateassociations between job stress and stroke andcoronary heart disease. Stress responses varywith age, gender, personality, behavior and atti-tude toward work, work skill, underlying dis-eases, and treatment status. Other factors, suchas relationships with supervisors or colleaguesat work, regulations and atmosphere in theworkplace, daily life outside work, and familyrelationships and role at home, modify stressresponses, and they also need to be examined.

Work-Related Stressors thatIncrease the Risk of Stroke andCoronary Heart Disease

Based on the results of previous studies andcases reported in Japan, there are three mainwork stressors related to stroke and coronaryheart disease.

The first stressor is the type of work, which isbased on the manner in which the work is per-formed. The second category is physical, chem-

Individual factors

Workplacestressors

Acute stressreactions

Stress-relateddisorders

Support from family, supervisors, colleagues

Off-work factors/demands from family or at home

Fig. 1 NIOSH occupational stress model

224 JMAJ, May 2004—Vol. 47, No. 5

trophy, systolic blood pressure elevation, andhigh serum cholesterol were more frequentlyobserved in the commercial pilot group, sug-gesting that shift work system is associated withtime difference, and that there is an associationbetween large time difference and stroke andcoronary heart disease.

3. Work-related psychological stressorsSome work stressors that induce mental

strain have sudden powerful effects, or power-ful effects for relatively short periods, andothers have repeated effects at work every dayover long periods. The latter will be examinedin this section.

Psychological stressors in the workplace andtheir effects have not been fully clarified, becauseevaluation of work stress is difficult. However,the concept of work stress and evaluationmethods have recently become established,and the reliability and validity of the methodhave been assessed. The number of findingsbased on these methods has been increasingand we will introduce one of the findings.

Karasek2) proposed a ‘job demand-control’model (Fig. 2) to evaluate psychological stressorsin the workplace. In this model, work-relatedpsychological stresses occur as the result of theinteraction between two factors. One factor isworkload and allocation of work, or so-called

office all night, in addition to actual workinghours, also needs to be considered as a probleminvolved in long working hours. Moreover,some studies have found that when work hoursare irregular and the changes of starting timeare more than 3 hours, the risk of myocardialinfarction is 2.53 times higher than when thechange in work hours is less than 1 hour. Thisindicates that irregular work hours may inter-fere with sleep-wakefulness rhythm and increasethe risk of stroke and coronary heart disease.Some negative research results have been re-ported for associations between cardiovasculardisease and shift work, night work, and earlywork, but many studies have reported a higherrisk of cardiovascular disease associated withchanges in shift work, ranging from approxi-mately 1.2 to 1.5 higher.

As to other types of work, work with manybusiness trips increases the risk of stroke andcoronary heart disease. Breaks and rests, in-cluding sleep time, and recovery from fatigueare keys to prevent such disease, especially inwork involving business trips to other countrieswith large time differences.

2. Physical, chemical, or ergonomic factors inthe workplace

Working in a cold environment induces oraggravates ischemic heart disease and cerebro-vascular disease. A temperature decrease of 10degrees Celsius has been found to be associ-ated with a 13% increase in the incidence ofattack in coronary artery, an 11% increase inmortality and incidence of coronary arterydisease, and a 26% increase in recurrence ofattack in coronary artery.

During chronic exposure to noise in a noisyenvironment (i.e., more than an 80 dB noiselevel), systolic and diastolic pressure elevation,high hypertension morbidity, a 1.2–1.4 highertimes relative risk of hypertension due to noise,and a direct association between noise andischemic heart disease have been observed.

In a comparative study between commercialpilots and a control group, left ventricular hyper-

Fig. 2 Job demand-control model

low highJob demand (intensity of work)

Job control (freedom of decision, or latitude)

Mental strain andrisk of disease

High job strain

high

low

F. KOBAYASHI

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‘job demand’, including the concentration anddegree of tension required to do the work,in other words, the intensity of the work. Theother factor is latitude, or the freedom ofexecution and decision at work, or what isreferred to as ‘job control’, under which talentsand skills can be demonstrated and improved.

According to Karasek’s model, psycholog-ical work stress is determined by these twofactors and the interaction between them. Thecombination of a high-level of job demand andlow-level of job control, that is, an environmentof hard work with little freedom, causes thehighest psychological stress and high risk ofdisease. Study of this ‘job demand-control’ modelhas mainly been conducted in Europe, andmany findings support the correlation betweenjob stress and cardiovascular disease. Thismodel is now one of the best models for evalu-ating job stress. Although few results have beenreported in Japan, a cohort study showed asignificantly lower level of job control amongworkers who were absent from work due tocardiovascular disease. Support by superiors orcolleagues, i.e., human relationships in theworkplace, as well as job demand and job con-trol, have been found to greatly modify theeffects of job stress. Cardiovascular diseasemortality and morbidity are high in groupswith severe work stress and little support fromsupervisors or colleagues, especially amongmanual workers.

In addition, Johnson et al. proposed the ‘jobdemand-control-support’ model.3) In this model,the combination of high-level of job demand,low-level of job control, and low social supportis associated with the highest level of mentalstrain and high risk of disease, such as strokeand coronary heart disease. This model is nowwidely accepted.

Psychological Stress in the Workplaceand the Pathogenetic Mechanisms ofStroke and Coronary Heart Disease

The mechanisms by which work-related psy-

chological strain affects the onset of stroke andcoronary heart disease have not been iden-tified, but the following have been suggested.First, work-related psychological strain mayincrease the cardiovascular risk associated withrisk factors such as smoking, drinking, bloodpressure, obesity, and low physical activity. Theoverall trend in previous research has shownrelatively negative results for an associationbetween job stress and serum lipids, and noconsensus has been reached in regard to smok-ing. Most studies report negative results for anassociation between job stress and casual bloodpressure, but a significant association has beenobserved with 24-hour blood pressure. There isa difference in blood pressure at home or in asleep between workers with high job strain andworkers with low strain, which suggests thatwork stress persists even when away from work.Also, it has been suggested that job stress causesdepression, leads to low physical activity, andinhibits the improvement of daily habits andcoronary risk factors.

Second, job stress may cause coronary arte-riosclerosis by other pathophysiological mecha-nisms. For example, some studies have shownan association between work stress and fibrin-ogen and HbA1c, which will be clarified infurther studies.

Third, at the stage of increasing risk of theonset of disease, psychological stresses in theworkplace may trigger the onset of fatal arrhyth-mia and cardiac infarction. The onset of thesediseases is presumably induced by excessivestimulation of the sympathetic nervous systemand a delay in recovery from decreased myo-cardial function. Some studies have shown thatworking until late at night causes excessivestimulation of the sympathetic nervous system,suppresses the parasympathetic nervous sys-tem, and causes blood pressure elevation,especially in hypertensive patients. We expectfuture studies to identify the effects of work-related psychological stresses in individualswho may have cardiovascular disease.

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Conclusion

Here we shall discuss the association betweenwork stress and stroke and coronary heart dis-ease. Type of work, including work hours, workenvironment, and work-related psychologicalstressors based on the characteristics of workhave been shown to be associated with theoccurrence of stroke and coronary heart dis-ease and the course of the disease after theonset. However, the mechanisms of the asso-ciations have not been clarified. Additionalfindings need to be obtained and assessed todetermine the association between work-relatedpsychological stressors and the pathogeneticmechanisms of stroke and coronary heart dis-ease in the workplace.

REFERENCES

1) Hurrell, J.J. and McLaney, M.A.: Exposure tojob stress-a new psychometric instrument.Scand J Work Environ Health 1988; 14(suppl1):27–28.

2) Karasek, R.A.: Job demands, job decision lati-tude, and mental strain: implications for jobredesign. Adm Sci Q 1979; 24: 285–307.

3) Johnson, J., Hall, E. and Theorell, T.: Com-bined effects of job strain ad social isolationon cardiovascular disease morbidity and mor-tality in a random sample of the Swedish maleworking population. Scan J Work EnvironHealth 1989; 15: 271–279.

F. KOBAYASHI