Introduction By Karen Belkic MD, PhD, and Peter Schnall MD, MPH
Cardiologists and other clinicians handling hypertension and ischemic heart disease are routinely called upon to make a judgment about cardiovascular work fitness of their patients. Unfortunately, however, the more fundamental question has rarely been posed in the clinical context. Namely, is the work environment fit, or conducive to cardiovascular health?
As recently summarized in The Workplace and Cardiovascular Disease: Occupational Medicine State of the Art Reviews (13), a large body of epidemiological as well as physiologic evidence has now accumulated implicating a number of workplace factors in the etiology of hypertension and ischemic heart disease (IHD). The evidence is particularly strong and consistent with respect to exposure to high strain work and risk of hypertension and IHD. Calculations of Population Attributable Risk (PAR%) indicate that between 20 and 30% of cases of hypertension among working men could be prevented by eliminating exposure to job strain. PAR% estimates suggest that possibly an even greater percentage of cardiovascular disease could be prevented by eliminating exposure to job strain, together with sedentary work, shift work and physical and chemical noxins. Current Trends in working life characterized e.g., by a rising level of exposure to job strain and long and irregular work hours, portend that work-related hypertension and IHD will become an increasingly important problem in the years to come.
Karen Belkic and Peter Schnall
Epidemiological Evidence-Convergent Validation of the Role of Workplace Factors in the Etiology of Hypertension and IHD
There is a burgeoning body of empirical investigation concerning the role played by workplace factors in the risk of hypertension and of ischemic heart disease (IHD) morbidity and mortality. The epidemiological evidence is most abundant and convincing with respect to psychosocial factors, especially job strain or its major components: high psychological demands and low decision-making latitude, as reviewed in: Ref. (10, 18, 40, 68, 69, 118). The association between exposure to job strain and cardiovascular disease is particularly pronounced among those with lower occupational status (37,49b, 136). Consistent data are also found for work requiring intensive effort, but providing relatively few rewards (“effort-reward imbalance”) (10, 81, 124,141). Furthermore, the combined effects of exposure to job strain and to effort-reward imbalance appear to be much stronger than the separate effects of each model (96). Night shift work (17, 59, 61, 88), long work hours (38, 49a, 127), exposure to noise (22, 29, 72, 132), temperature extremes (77, 145), as well as chemicals such as carbon monoxide, lead and carbon disulfide (43, 45, 63, 89, 93), inter alia, are also implicated, on the basis of positive epidemiological studies, as possible risk factors for hypertension and/or IHD.
Certain occupational groups with exposure to a large number of workplace stressors are found to be at high risk for developing hypertension and IHD. Here the evidence is strongest with respect to professional drivers (9, 139, 148), whose work requires the maintenance of sustained vigilance, whereby an error or momentary lapse of attention can have serious, potentially fatal consequences (“threat-avoidant vigilant work”), and who face a heavy overall burden from potentially cardio-deleterious workplace factors (7). Rosengren, Anderson & Wilhelmsen (109) found that the increased risk of coronary heart disease was independent of standard risk factor status. After a mean of 11.8 years of prospective study, these authors reported an odds-ratio (OR) of 3.3 (95% Confidence Interval (CI)=2.0-5.5) for coronary heart disease among 103 middle-aged male mass transit drivers in Gothenberg with respect to 6596 men from other occupational groups. After accounting for age, serum cholesterol, blood pressure, smoking, body mass index, diabetes, positive parental history of CHD and physical activity, as well as socio-demographic factors, the risk decreased only slightly (OR=3.0, 95% CI=1.8-5.2).
Finally, epidemiological studies among working people reveal that systolic ambulatory blood pressure (AmBP) is on the average 5mmHg higher during the hours on the job compared to leisure time (33, 117, 120) and that mean 24-hour AmBP is lower on non-work days compared to work days (101, 102). There is also evidence of a septadian overrepresentation of acute cardiac events on Mondays (106, 147), and automatic implantable cardioverter-defibrillators are seen to fire significantly more on Mondays (97). These findings corroborate the statements of Lown (78) that “the stress of work after a weekend of respite may have been the precipitants of lethal arrhythmias” (p. I-188) and of Willich and colleagues (147) that “an increase in physical and mental burden from leisurely weekend activities to stressful work on Monday in the majority of working patients” could be causally related to the occurrence of acute MI (p.90).