Background Two main theoretical models have been used to assess the impact of psychosocial work factors on blood pressure (BP): the demand–control (DC) model and the effort–reward imbalance (ERI) model. Previous studies have mostly used a single time point exposure to examine this association.
Objective To examine the effect of repeated job strain and ERI exposure on (1) ambulatory BP (ABP) evolution over 5 years and (2) hypertension incidence over 5 years.
Method The design is a prospective cohort study. The study population was composed of 1394 white-collar workers (568 men and 826 women). They were assessed three times during a 5-year period (years 1, 3 and 5). At each time, psychosocial work factors were measured using validated scales and ABP was measured every 15 min during a working day.
Results Men who were chronically exposed over 5 years to an active job had a higher cumulative incidence of hypertension (RR=2.05, 95% CI 1.36 to 3.09), compared with never-exposed men. In women, ERI exposure onset was associated with higher increases in systolic ABP (+2.5 mm Hg). No association was found between chronic high-strain exposure and ABP.
Conclusions Chronic exposure to active jobs in men led to a higher risk of hypertension and ERI exposure onset in women led to increases in systolic ABP. Results from the present study highlight the need to consider chronic exposure in order to fully capture the deleterious effect of adverse psychosocial work stressors on cardiovascular health.
- BLOOD PRESSURE
- Work stress
- OCCUPATIONAL HEALTH
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Cardiovascular diseases (CVD) are major causes of illness, disability and death in industrialised countries.1 High blood pressure (BP) is a major CVD risk factor.2 The risk of cardiovascular mortality rises linearly with BP from 115/75 mm Hg in adults aged 40–69 years with no history of CVD.3 Epidemiological studies have documented the effect of adverse psychosocial factors at work (work stress) on CVD4 ,5 and high BP.6–9
Two main theoretical models are mainly used to assess the impact of psychosocial work factors on BP. The demand–control (DC) model suggests that workers simultaneously experiencing high psychological demands (PD) and low decision latitude (DL), that is, job strain, are more likely to develop stress-related health problems.10 PD refer to an excessive work load, very hard or very fast work, task interruption, intense concentration, and conflicting demands. DL is a combination of skill discretion and decision authority. The second model, Siegrist's11 effort–reward imbalance (ERI) proposes that efforts at work should be rewarded in various ways: income, respect and esteem, and occupational status control. Workers are in a state of detrimental imbalance when high efforts are accompanied by low reward, and thus more susceptible to health problems.
Previous studies which have evaluated the effect of psychosocial work factors on BP have, for the most part, used a single time point exposure.7 Measuring psychosocial work factors at multiple time points makes it possible to take changes in exposure into account. It also makes it possible to identify chronically exposed workers, who may have a higher cardiovascular risk than workers exposed for a shorter period. Previous studies have examined the effect of repeated job strain or ERI exposure on BP.12–19 Those studies however have limitations such as small sample size12–14 ,16 and the use of casual BP measurements.17–19 There is strong evidence supporting the superiority of ambulatory BP (ABP) measurements over standard office BP measurements in terms of reliability and validity.20
The objective of the present study was to examine the effect of repeated job strain and ERI exposure over 5 years (years 1, 3 and 5) on (1) ABP evolution over 5 years and (2) hypertension incidence over 5 years.
Population and study design
The design is a prospective cohort study. The study population was composed of white-collar workers from three public insurance institutions in Quebec City, Canada. Their main activities involved organising and providing insurance services to the general population. Their jobs encompassed the full range of white-collar positions, including senior and middle managers, professionals, and technicians and office workers. Workers completed a self-administered questionnaire on work characteristics and BP risk factors. Data collection was performed at three time points: at baseline (2000–2004), 3 years later (2004–2006), and 5 years later (2006–2009). The participation rate was 80.9% at baseline. Figure 1 presents a flowchart of the study population. At baseline, there were 2135 eligible workers. About 15% of these eligible workers were excluded at each follow-up, mainly because they were lost or refused to participate (N=295), they retired (N=231) or because they had no or insufficient ABP measurements (N=159). In the hypertension incidence analysis, participants with hypertension or being treated for hypertension at baseline were excluded, and treated participants at follow-ups were categorised as incident hypertensives. The final study population was composed of 1394 workers, namely 568 men and 826 women for ABP means analyses and of 999 workers (345 men and 654 women) for hypertension analyses.
Psychosocial work factors
We measured both components of the DC model using 18 items from the Job Content.21 PD reflect quantity of work, time constraints, and level of intellectual effort required. DL reflects opportunities for learning, autonomy and participation in the decision-making process. The psychometric properties of the original whole Job Content Questionnaire (JCQ) scale of 18 items22 ,23 and its French23–26 version have been previously demonstrated. We have used the proposed quadrant method to classify participants in four groups. Workers with PD scores of 24 or higher (the median for the general Quebec working population) were classified as having high PD. Workers with DL scores of 72 or lower (median of general Quebec working population) were classified as having low DL.27 The passive group comprised workers with low PD and low DL, the active group comprised workers with high PD and high DL, and the job strain (high-strain) group comprised workers with high PD and low DL. Other workers were classified as unexposed. For the repeated exposure analyses, workers exposed to high strain were considered exposed while other workers were classified as unexposed, at each time. Repeated active and passive exposures were considered using the same strategy, that is, using a binary variable at each measurement time. The effect of chronic exposure to intermediate job strain categories was hypothesised a priori, given available evidence for an effect of these exposures on BP.28–30
Reward was assessed using the French version of the 11 original items recommended by Siegrist.11 The items were divided into three scales: esteem (five items), promotions and salary (four items), and job security (two items). The factorial validity and internal consistency of both versions (English and French) have been demonstrated.31 Effort was measured with two original items of the Siegrist questionnaire (“over the past few years, my job has become more and more demanding” and “I am regularly forced to work overtime”), and with two proxies (“my tasks are often interrupted before they can be completed, requiring attention at a later time” and “I have enough time to do my work”) (Cronbach's α=0.69). For the baseline exposure analyses, the ERI ratio was divided into tertiles. For the repeated exposure analyses, a ratio of efforts to rewards greater than 1 indicated an ERI, at each time.
Repeated exposure definition
Workers were classified according to repeated job strain, active, passive and ERI exposure, using, at each time, the binary variables described above. Workers were then classified as either being never exposed (0, 0, 0); having intermittent exposure (0, 1, 0 or 1, 0, 1); having exposure cessation (1, 0, 0 or 1, 1, 0); having exposure onset (0, 1, 1 or 0, 0, 1) or being chronically exposed (1, 1, 1).
Ambulatory blood pressure
At each measurement time (years 1, 3 and 5), ABP was assessed by the Spacelabs 90207 oscillometric devices (Spacelabs Produits Médicaux Ltée, St-Laurent, Quebec, Canada) validated by the independent investigators’ protocol, recommended by the Association for the Advancement of Medical Instrumentation and British Hypertension Society.32 ,33 In the present study, participants must have been measured at least 20 times, which is in accordance with more stringent criteria recently recommended by expert committees.34 The first three measures, taken in presence of staff, were excluded. ABP was defined as the mean of all subsequent readings taken during the working day. The device was installed on the non-dominant arm if BP difference measured on both arms was inferior to 10 mm Hg. Otherwise, it was installed on the arm showing the higher BP level. ABP was measured every 15 min during daytime working hours. Participants were white-collars workers whose tasks were mainly achieved in a sitting position. To minimise motion artefact, clear instructions were given to participants in the case where the monitor performed a reading while they were in a standing position (stopped walking with their arm resting at their side). ABP changes where measured using the difference between years 5 and year 1 ABP. Ambulatory hypertension was defined as daytime systolic or diastolic ABP greater than or equal to 135 mm Hg and 85 mm Hg, respectively, or being treated for hypertension.35
Several factors were considered as potential confounders including cigarette smoking status, body mass index (BMI), alcohol intake and physical activity. Smoking status was defined as the daily consumption of at least one cigarette per day. Body weight and height were measured to calculate BMI (kg/m2) which was categorised using the following categories: <25, 25–29.9 and ≥30 kg/m2. Alcohol intake was measured using the following three categories, related to weekly intake frequency during the past 12 months: less than 1 drink per week, 1–5 drinks per week, and 6 and more drinks per week. Participants were further classified by their weekly leisure physical activity frequency (<1/week/≥1/week). Other factors also considered as potential confounders were age (<40, 40–49, ≥50 years old), education (less than college, college completed, university completed), medication for hypertension, and family history of CVD. The definition of the latter group was based on the declaration by the participant of a cardiovascular event, such as angina, myocardial infarction, coronary revascularisation or stroke, suffered by their father, mother, brother or sister before the age of 60 years. The risk factors listed above were evaluated using validated protocols.27 ,36
Student t test and χ2 analyses were used to compare baseline characteristics among men and women. Analysis of covariance (ANCOVA) was used to study the association between job strain, active and ERI exposure and ABP difference over 5 years. p Values were computed. The level of statistical significance was set at the 0.05 level. All comparisons with the reference group were conducted by using Dunnett's adjustment for multiple comparisons. Cumulative incidence of hypertension were modeled using robust Poisson regression,37 and risk ratios were computed with 95% CIs. It should be noted that lifestyle risk factors might act as mediating variables, that is, intervene in the causal pathway linking work stress to BP.38 We have therefore examined two set of adjusted models: (1) adjusted for sociodemographic and BP-related variables (age, education, medication for hypertension and family history of CVD) and (2) additionally adjusted for lifestyle-related risk factors (smoking, BMI, physical activity and alcohol intake). Since both yielded similar estimates, we reported results from the fully adjusted models only. Analyses were conducted separately in men and women, given the available evidence supporting a gender-specific relationship between adverse psychosocial work factors and cardiovascular health.38 All analyses were performed with SAS V.9.4 software.39
Table 1 summarises participants’ characteristics. Participants were 40.7% men and 59.3% women. The participants’ mean age was 43.3 years for men (SD=7.4) and 42.3 years for women (SD=6.2) (p<0.001). Women were generally less educated than men. They had lower BMI and consumed less alcohol. However, women were more likely to smoke, maintain a sedentary lifestyle or have a known history of CVD. Mean systolic and diastolic ABP was 128.8/81.9 mm Hg in men (SD=9.8/7.3) and 121.2/78.1 mm Hg in women (SD=10.1/7.3) (p<0.001). The cumulative incidence of hypertension was 30.7% in men and 17.7% in women.
Table 2 presents ABP changes over 5 years according to repeated job strain and ERI exposure over 5 years. Chronic high-strain exposure was not associated with ABP changes over 5 years, in either men or women. There was an unexpected lowering of systolic ABP in men with job strain exposure onset (−2.7 mm Hg), which was not observed for diastolic ABP. Men who were chronically exposed to an active job had higher systolic (+2.2 mm Hg) and diastolic (+1.8 mm Hg) ABP increases, compared with never-exposed men but these differences in ABP increases were not statistically significant. In women, ERI exposure onset was associated with systolic (+2.5 mm Hg) ABP increases.
Table 3 presents the cumulative incidence ratios (CIR) of hypertension over 5 years according to repeated job strain, active and ERI exposure. Repeated job strain exposure was not associated with the incidence of hypertension, in either men or women. In men the cumulative incidence of hypertension was 2.05 (95% CI 1.36 to 3.09) fold higher among those chronically exposed to an active job, than among those who had never been exposed, after all adjustments. In women, CIR were higher, for job strain exposure onset (RR=1.38; 95% CI 0.87 to 2.18) and ERI exposure onset (RR=1.41; 95% CI 0.79 to 2.52).
In this prospective study, men who were chronically exposed to an active job over 5 years had a higher cumulative incidence of hypertension over 5 years, compared with never-exposed men. Women experiencing onset of ERI exposure had higher systolic ABP increase compared with never-exposed women. These findings support the relevance of considering repeated exposure in further prospective studies.
Most,12 ,14–18 but not all13 ,19 previous studies have reported higher BP for workers chronically exposed to high strain. In the present study, hypertension incidence in men was higher among men chronically exposed to an active job situation. This association do no fully correspond with Karasek and Theorell's theoretical proposition.10 The DC model hypothesised that active jobs are associated with a feeling of mastery which could reduce the psychophysiological impact of stressful situations at work resulting in better cardiovascular health.10 The worse cardiovascular profile observed for active workers might be partly attributable to new management practices, which have led to work intensification.40 These practices (downsizing, poor job security, decline in permanent jobs and growth of temporary/fixed contract work) involve increased productivity expectations and results obligations, combined with a higher autonomy over work. In such conditions, high demands may be too high to be compensated by gain in job control. These changes and their related work conditions might alter and/or complexify the pathogenic process linking demands, control and cardiovascular health.
Only one previous study has prospectively examined the effect of ERI exposure on ABP.15 In this previous study, women <45 years old exposed to ERI at baseline and follow-up or at follow-up only had significantly higher systolic and diastolic ABP increases at follow-up than those unexposed, within a 3-year follow-up. In the present study, ERI exposure onset but not chronic exposure over 5 years was associated with ABP increases, in women. This finding might be explained by an habituation process where the magnitude of the physiological response to ERI exposure decreases over time, after being exposed for a prolonged period.41 It could also be explained by a selection effect (healthy worker effect), were women who had higher ABP quitted because of their condition.42
We have reported results unadjusted for baseline ABP. High baseline ABP values may be the consequence of faster increases before the study's baseline measurement.43 This effect, described as the horse-racing effect, is most likely to occur in observational cohort studies such as ours.44 If this is the case, baseline-adjusted models could lead to underestimations of the true effect of psychosocial work factors on ABP evolution. The retained strategy is more likely to provide unbiased causal effect estimates, compared with baseline-adjusted estimates.45 Baseline-adjusted analyses were computed and yielded similar estimates (see online supplementary table S1).
There is also no clear consensus regarding the best way to deal with patients treated for hypertension in epidemiological studies. Selection bias occurs when participants with higher ABP and therefore presumably higher exposure to psychosocial work factors are excluded, resulting in an underestimation of the effect. On the other hand, including participants for whom BP levels had been lowered by medication results in misclassification of the outcome and could therefore also lead to a bias towards the null. A sensitivity analysis was conducted excluding patients treated for hypertension and yielded estimates of comparable magnitude (see online supplementary table S2).
Our study has some limitations. First, the associations observed could have been underestimated due to a selection bias in loss at follow-up. In men, losses at follow-up had higher ABP means at baseline compared with study participants (p<0.01), for both systolic and diastolic ABP (132.1/84.1 vs 129.4/82.3 mm Hg) while no difference was found in women. Job strain and ERI exposure at baseline was comparable between losses and participants, in men and women. The selective drop out were thus related to the outcome but not related to baseline exposure therefore limiting the possibility of an important selection bias. Second, misclassification biases are also possible. Such a bias may have been introduced by the use of a binary exposure definition, at each measurement time, in the repeated exposure analyses. Our definition of repeated exposure nonetheless minimised exposure misclassification, when compared with a single time point assessment. A misclassification bias may also have been introduced by the four-point Likert scale used to assess ERI items. However, at follow-up, four-point and five-point original scales were available and showed satisfactory correlations (r=0.78 for effort and r=0.80 for reward). Finally, the study population was composed of white-collar workers so results may not generalise to other populations.
Our study has important strengths: (1) it involved a large sample of white-collar workers; (2) the high participation rate; (3) the use of repeated job strain and ERI exposure allowing cumulative exposure to be accounted for; (4) it was conducted among men and women, thus allowing the investigation of gender-specific relations; (5) the use of ABP measurements and (6) the use of validated scales to assess psychosocial work factors from DC and ERI models.
Associations between adverse psychosocial work factors and ABP found in the present study, although modest, may have an important impact on population health. Indeed, at the population level, a 2 mm Hg reduction in mean systolic BP would result in 10% fewer deaths from stroke and about 7% fewer death from ischemic heart and vascular diseases in middle age.46 ,47 Adverse psychosocial work factors are modifiable48 and their prevalence is estimated to be 15–30% in industrialised countries.49 The implementation of preventive interventions aiming at reducing these factors might result in important beneficial effects on cardiovascular health.
Chronic exposure to active jobs in men led to a higher risk of hypertension and ERI exposure onset in women led to increases in systolic ABP. No effect was found using high-strain exposure. Results from the present study highlight the need to consider repeated exposure over time in further prospective studies examining the effect of adverse psychosocial work factors on cardiovascular health.
What is already known on this subject
The prevalence of adverse psychosocial work factors is estimated to be 15–30% in industrialised countries.
A growing body of research has investigated the adverse effects of psychosocial work factors from the demand–control model and from the effort–reward imbalance model on cardiovascular health.
Previous studies have mostly used a single time point exposure to examine this association.
What this study adds
In the present study, conducted in a large sample of white-collar workers, chronic exposure to active jobs in men led to a higher risk of hypertension and ERI exposure onset in women led to increases in systolic ambulatory blood pressure.
Measuring repeated exposure to adverse psychosocial work factors makes it possible to identify chronically exposed workers, who are at higher cardiovascular risk than workers exposed for a shorter period.
Preventive interventions aiming at reducing these adverse factors might result in meaningful effects on cardiovascular health.
This web only file has been produced by the BMJ Publishing Group from an electronic file supplied by the author(s) and has not been edited for content.
- Data supplement 1 - Online supplement
Contributors XT supervised and synthesised the data analyses and led the writing. CB originated and supervised all aspects of the study. AM supervised the aspects of the study related to blood pressure measurement and interpretation. MV supervised the public health and work-related issues of the study. BM supervised data analyses. All the authors participated in reviewing and drafting of the manuscript.
Funding This research was supported by a grant from the Canadian Institutes of Health Research (grant number #57750). CB was a Canadian Institutes of Health Research investigator when this work was conducted.
Competing interests None declared.
Ethics approval This study was approved by the ethical review board of the CHU de Québec.
Provenance and peer review Not commissioned; externally peer reviewed.
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