Work-related psychosocial factors and carotid atherosclerosis

M Rosvalla, P-O Östergrena, B Hedblada,b, S-O Isacssona, L Janzona and G Berglundb

a Department of Community Medicine
b Department of Medicine, Orthopedics and Surgery, Lund University, Malmö University Hospital, Malmö, Sweden.

Correspondence: Maria Rosvall, Department of Community Medicine, Malmö University Hospital, SE-205 02 Malmö, Sweden. E-mail: maria.rosvall{at}smi.mas.lu.se

Abstract

Background In order to better understand the role of work environment in the earlier stages of the cardiovascular disease process, we wanted to investigate the influence of work-related psychosocial factors on preclinical atherosclerosis.

Methods Cross-sectional data was used to examine the association between psychological job demands, job decision latitude, and carotid atherosclerosis in 2658 vocationally-active Swedish men and women, ages 46–65, from the general population. Odds ratios of carotid plaque prevalence and carotid artery intima-media thickness (IMT), determined by B-mode ultrasound, were estimated across combinations of job demands and decision latitude.

Results Women in job situations with high demands and low decision latitude (‘job strain’) showed a high plaque prevalence odds (odds ratio [OR] = 1.68, 95% CI: 1.14, 2.48), and a thicker IMT in the carotid bifurcation area (mean difference: 0.15 mm, 95% CI: 0.07, 0.23) compared with women in job situations with low demands and high decision latitude (‘relaxed’). Adjustment for covariates only slightly reduced the magnitude of these associations. No such associations were seen in men. However, women in job situations with high demands and high decision latitude (‘active’) also showed high odds for carotid plaque, and a thicker IMT in the carotid bifurcation, compared with women in ‘relaxed’ job situations. In men, those in ‘active’ job situations had a low carotid plaque prevalence odds, while IMT in the carotid bifurcation did not differ from those in ‘relaxed’ job situations. Results showed only weak associations with IMT in the common carotid artery (CCA) in both men and women.

Conclusion The specific hypothesis that high job demands interact synergistically with low decision latitude in the development of carotid atherosclerosis could not be supported in this study, neither in men nor in women. Instead a more complex pattern of interaction between job demands and decision latitude was shown.

Keywords Atherosclerosis, carotid arteries, ultrasonography, stress, work, psychosocial factors, sex factors

Accepted 17 July 2002

The past 20 years has seen the growing recognition of work-related psychosocial factors in the aetiology of coronary heart disease.1–4 Research in this area has been dominated by the ‘job strain’ model developed by Karasek5 and colleagues.6 It has been shown that those job situations characterized by high psychological demands and low decision latitude (i.e. little opportunity to be creative or use and develop skills) are associated with increased risk of cardiovascular disease.7

In spite of many studies on the relationship between psychosocial factors and cardiovascular disease, there is no agreement on the mechanisms by which this effect is mediated. Generally, studies of job strain and cardiovascular disease have shown more consistent results than studies of job strain and cardiovascular risk factors.8 Job strain has been found to influence the adoption of unhealthy behaviours, such as smoking, physical inactivity and high fat intake,9–11 increased blood pressure,12,13 and fibrinogen levels.14 However, other studies found no such relationships.15,16 Furthermore, few of the studies mentioned have been conducted among women.

In reviewing the research in this field, Kasl suggested that the influence of psychosocial factors should be studied at different stages in the cardiovascular disease process.17 Prior research had mainly focussed on such complications in the late stages of atherosclerotic disease, e.g. myocardial infarction. Only a few studies (none involving women) have addressed the earlier stages of cardiovascular disease, i.e. the clinically latent part of the atherosclerotic process.18,19

Technical advances in ultrasound scanning now make it possible to observe the process of atherogenesis non-invasively at different vascular beds in the general population.20,21 The extent of carotid atherosclerosis is known to reflect general atherosclerosis,20 and especially the magnitude of coronary atherosclerosis.22 Examination of carotid atherosclerosis by ultrasound thus provides the opportunity of studying factors of importance for preclinical atherosclerosis, and also serves to reduce the risk of selection bias because of downward socioeconomic mobility due to manifest cardiovascular disease.

Using a general population sample, we investigated the association between psychological job demands and job decision latitude with regard to preclinical manifestations of atherosclerosis, as evidenced by intima-media thickness (IMT) and atherosclerotic plaques in the carotid arteries. Job situations characterized by high psychological demands and low decision latitude (‘job strain’) were hypothesized as increasing the development of carotid atherosclerosis in both men and women. We also wanted to examine the contributions of socioeconomic status, biological factors, lifestyle factors, psychosocial factors unrelated to work, and domestic stress within this context.

Subjects and Methods

Study population
The subjects in this study constituted a sub-cohort of the large, population-based Malmö Diet and Cancer Study (MDCS).23 A random 50% of those born between 1926 and 1945 who entered this study from October 1991 to February 1994 were invited to take part in an investigation of the epidemiology of carotid artery disease.24 We included individuals who had completed a self-administered questionnaire at the baseline examination (n = 4884). A total of 480 potential subjects were excluded due to incomplete laboratory test results or because of an excessive time lag between their ultrasound, baseline, and laboratory examinations.25 An additional 228 individuals who had a history of cardiovascular disease were also excluded. Subjects were considered to have cardiovascular disease if their answers on the baseline questionnaire confirmed treatment or hospitalization for myocardial infarction, stroke, or intermittent claudication. Our analysis was further restricted to currently employed individuals (69% of the sample population), yielding a study population of 2658 subjects (1550 women and 1108 men).

Occupational status was classified according to the criteria of Statistics Sweden into five socioeconomic index groups on the basis of questions concerning job designations and specific duties.26 This classification takes into consideration the educational background needed for a job, the level of responsibility within the organization, and the actual work tasks. Based on two-digit socioeconomic status codes, five occupational groups were constructed: (1) high-level non-manual employees (i.e. those in management positions and professionals with university degrees); (2) medium-level non-manual employees (i.e. registered nurses, computer operators, and teachers); (3) low-level non-manual employees (i.e. office-assistants, sales staff, and secretaries); (4) skilled manual workers (i.e. vehicle mechanics, metal workers, and construction workers); and (5) unskilled manual workers (i.e. factory workers, waiters, and custodial staff).

Psychosocial working conditions
Psychosocial work exposure was assessed by an instrument developed by Karasek and Theorell to measure psychological job demands and job decision latitude.6 Individuals were given five questions assessing psychological job demands and six questions on decision latitude, and were instructed to respond on a scale from 1 to 4. Overall scores for each category were calculated using the sum of weighted items, as suggested by Karasek.6 The scores for the two categories were dichotomized at the median and combined into four groups: (1) job situations characterized by high demands and low decision latitude (‘job strain’); (2) job situations with high demands and high decision latitude (‘active’); (3) job situations with low demands and low decision latitude (‘passive’); and (4) job situations with low demands and high decision latitude (‘relaxed’). The last group was used as a reference group.

Atherosclerotic risk factors
Atherosclerotic risk factors were estimated by means of laboratory tests, baseline examinations, and a questionnaire administered at baseline. Details of assessment procedures regarding smoking habits (‘never’, ‘former’, and ‘current smoker’), alcohol intake (g/week), leisure-time physical activity, diabetes mellitus, measurements of blood pressure (mmHg), low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, treatment for hypertension, and body mass index (BMI) (kg/m2) have been reported previously.25 Social network was operationalized as participation in formal and informal social groups, such as attending the theatre, church, evening courses, and sports activities.27,28 Social support unrelated to work was operationalized as emotional support reflecting the individual’s experience of receiving care and personal encouragement, and having feelings of confidence and trust.27,28 These instruments have been evaluated for reliability and validity in a previous study29 and they have been found to be associated with cardiovascular risk factors, and to predict cardiac event rate and overall mortality.27,30 Scores from each index were dichotomized into high/low as close to the lowest tertile as possible. Cohabiting status was measured and dichotomized into ‘living alone’ or ‘living with someone’. Working hours per week were defined either as ‘regular’ or ‘overtime’ (the latter if it was a weekly occurrence).

Domestic responsibilities and neighbourhood educational level
Household work was assessed by questionnaire as the sum of hours/week devoted to household duties, including shopping. Whether or not the subject had children at home was also assessed by questionnaire. Data on the educational level of neighbourhoods in Malmö was obtained from the Municipal Office, Malmö. Low educational level areas were defined as those neighbourhoods having a proportion of residents with <=9 years of education exceeding the median value for all neighbourhoods in our sample (median = 39.6%).

Carotid atherosclerosis
Carotid atherosclerosis was assessed by B-mode ultrasound. The examination procedure and image analysis, which have been described previously,24 were performed by specially trained sonographers certified on completion of an extensive educational programme.31 In brief, the right carotid bifurcation was scanned within a predefined window comprising 3 cm of the distal common carotid artery (CCA), the bifurcation, and 1 cm of the internal and external arteries for the occurrence of plaques, defined as focal IMT >1.2 mm. The IMT was determined in the far wall according to the leading edge principle as the mean wall thickness in the CCA 1 cm proximal to the bifurcation and as the maximum IMT in the bifurcation area.

Statistical analysis
Differences in risk factor patterns and domestic stress by work-related psychosocial factors were assessed for continuous variables by linear regression models and for dichotomous variables by logistic regression models. Differences in IMT between categories of psychosocial work conditions were analysed by multiple linear regression models (SPSS computer software, V. 10.0). Odds ratios (OR) for carotid plaque prevalences were estimated by logistic regression models. Adjustments for covariates were made in five steps. First, including only lifestyle factors (smoking, alcohol consumption, and physical activity). Second, including only biological risk factors (LDL cholesterol, HDL cholesterol, systolic blood pressure, treatment for hypertension, the presence of diabetes mellitus, and BMI). Third, including only psychosocial factors unrelated to work (social participation, emotional support, and cohabiting status). Fourth, by including only other work-related and domestic covariates (number of working hours, overtime, household duties/week, presence of children at home, and educational level of neighbourhood). The fifth regression model included all covariates. Ordinal variables were introduced as dummy indicators in the analyses.

Results

Study population
Table 1Go presents the study population. Men were more likely than women to be ex-smokers, to work more regular hours/week, put in more overtime, and to hold occupations classified as medium- or high-level non-manual. Men were less likely than women to have a job situation characterized by low decision latitude. As compared to women, men generally had a higher prevalence of carotid plaques and thicker carotid intimal-medial walls.


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Table 1 Study population by sex, sociodemographic characteristics, physiological measurements, health-related behaviours and level of self-reported psychological job demands, and job decision latitude. Values are numbers and percentages unless stated otherwise
 
Distribution of work-related psychosocial factors
Table 2Go shows the distribution of work-related psychosocial factors according to the model defined by Karasek. Proportionately more men than women had job situations with low demands and high decision latitude (‘relaxed’), or job situations with high demands and high decision latitude (‘active’). Women were more likely to have job situations with low demands and low decision latitude (‘passive’) or job situations with high demands and low decision latitude (‘job strain’).


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Table 2 Study population by combinations of psychological job demands, and job decision latitude in middle-aged Swedish men and women
 
Atherosclerotic risk factors by work-related psychosocial factors
With few exceptions, behavioural and physiological risk factors were found to vary only moderately with psychosocial working conditions, whereas psychosocial factors unrelated to work showed strong associations with psychosocial working conditions in both men and women (Table 3Go). Women in job situations with high psychological demands and high decision latitude (‘active’) showed a high prevalence of smoking. Such women also worked more hours per week, and put in more overtime work than women in job situations with low psychological demands and high decision latitude (‘relaxed’) (reference group).


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Table 3 Age-adjusted means and prevalences (%) of physiological measurements, health-related behaviours, psychosocial factors, carotid plaque and carotid intima-media thickness by work-related psychosocial factors in middle-aged Swedish men and women
 
Domestic duties by work-related psychosocial factors
Table 4Go shows the age-adjusted distribution of various domestic duties and educational level of the neighbourhood by work-related psychosocial factors. Generally, more time was spent doing household work by women than men. Women in job situations with high psychological demands and high decision latitude (‘active’) or high psychological demands and low decision latitude (‘job strain’) spent the most time doing household chores. For both men and women, those in job situations with low psychological demands and low decision latitude (‘passive’) or high psychological demands and low decision latitude (‘job strain’) more often lived in neighbourhoods with a high proportion of residents with only primary education compared to those in the ‘relaxed’ job situation.


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Table 4 Age-adjusted means and prevalences (%) of domestic duties and educational level of neighbourhood by work-related psychosocial factors in middle-aged Swedish men and women
 
Carotid plaque by work-related psychosocial factors
The age-adjusted odds of carotid plaque tended to be higher for women in job situations with high psychological job demands (OR = 1.27, 95% CI: 1.00, 1.63), but not for men in this situation. There was no association between having a job situation with low decision latitude and presence of carotid plaque for either men or women (data not shown).

When examining the combined effect of job demands and job decision latitude on the presence of carotid plaque (Table 5Go), women in job situations with high psychological demands and low decision latitude (‘job strain’) showed a high plaque prevalence odds compared to women in job situations with low psychological demands and high decision latitude (‘relaxed’) (reference group). Such a pattern was not seen in men. Men in job situations with high psychological demands and high decision latitude (‘active’) had a low carotid plaque prevalence odds (OR = 0.71, 95% CI: 0.51, 0.99) compared to men in ‘relaxed’ job situations. Among women, the pattern was reversed, with women in job situations with high psychological demands and high decision latitude (‘active’) having the highest carotid plaque prevalence odds. Also women in job situations with low psychological demands and low decision latitude (‘passive’) had a relatively high odds of carotid plaque. After adjusting for covariates, the magnitude of the associations in men remained nearly unchanged, while the associations found in women were slightly reduced—with the association with ‘job strain’ becoming of borderline significance (P = 0.06).


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Table 5 Adjusted odds ratios (OR) and 95% CI of carotid plaque, by self-reported work-related psychosocial factors in middle-aged Swedish men and women
 
Finding that men in job situations with low psychological demands and high decision latitude (‘relaxed’) had a relatively high prevalence of carotid plaque, we considered the possibility of a threshold effect dependent on the choice of cut-off limits when dichotomizing the two variables. Changing the cut-off threshold of psychological job demands to the lowest tertile, however, did not lead to any major changes in the magnitude of the associations initially found (data not shown). Men in ‘active’ job situations still had the lowest carotid plaque prevalence odds (OR = 0.62, 95% CI: 0.44, 0.89), while those in ‘relaxed’ job situations had the highest odds. Conversely, women in ‘active’ job situations had a relatively high carotid plaque prevalence odds (OR = 1.77, 95% CI: 1.16, 2.71). Similarly, changing the cut-off border of work-related decision latitude to the highest tertile did not change the magnitude of these associations (data not shown).

There were only minor changes in the relationship between psychosocial working conditions and carotid plaque in men after adjusting for occupational status. The age and occupational status adjusted OR of carotid plaque for psychosocial working conditions (‘relaxed’ job situation (reference group), ‘active’ job situation, ‘passive’ job situation, and ‘job strain’) were 0.73 (95% CI: 0.45, 1.03), 0.87 (95% CI: 0.46, 1.16) and 0.91 (95% CI: 0.59, 1.41), respectively. Among women, the magnitude of the associations between psychosocial working conditions and carotid plaque was slightly reduced. Corresponding OR of carotid plaque for women were 1.82 (95% CI: 1.21, 2.62), 1.45 (95% CI: 0.96, 1.73) and 1.45 (95% CI: 0.94, 1.95).

Intima-media thickness in the carotid bifurcation area by work-related psychosocial factors
Women in job situations with high job demands showed a thicker IMT in the carotid artery bifurcation area compared with women in job situations with low job demands (mean difference = 0.08 mm; 95% CI: 0.03, 0.14). Women in job situations with low decision latitude also showed a thicker IMT compared with those in job situations with high decision latitude (mean difference = 0.06 mm; 95% CI: 0.003, 0.12). No such associations could be seen in men (data not shown).

When examining the combined effect of job demands and job decision latitude on IMT in the carotid bifurcation area, there were similar patterns of associations as to those found for carotid plaque. Table 6Go shows that women in job situations characterized by ‘job strain’ had a thicker IMT compared to women in ‘relaxed’ job situations, (mean difference = 0.15 mm; 95% CI: 0.07, 0.23). No such association was found in men. Furthermore, women in ‘active’ job situations had a thicker IMT compared to women in ‘relaxed’ job situations, (mean difference = 0.10 mm; 95% CI: 0.01, 0.19). The magnitude of these associations was somewhat attenuated after adjustment for covariates, where the difference in IMT between those in ‘active’ job situations and those in ‘relaxed’ job situations turned to borderline significance (P = 0.11).


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Table 6 Adjusted mean differences (mm) and 95% CI in carotid intimal-medial wall thickness in the bifurcation area, by self-reported work-related psychosocial factors in middle-aged Swedish men and women
 
Intima-media thickness in the common carotid artery by work-related psychosocial factors
In both men and women, the age-adjusted mean differences in IMT in the CCA by psychosocial working conditions were small and statistically non-significant (data not shown). For example, men in job situations characterized by ‘job strain’ and men in job situations with high psychological demands and high decision latitude (‘active’) showed a similar IMT compared to men in ‘relaxed’ job situations, (mean difference = -0.01 mm; 95% CI: –0.04, 0.02, and mean difference = -0.001 mm; 95% CI: –0.02, 0.02, respectively). For women, the corresponding figures were: mean difference = -0.008 mm; 95% CI: –0.03, 0.01, and mean difference = 0.002 mm; 95% CI: –0.02, 0.02 respectively.

Discussion

Women in job situations with high psychological demands and low decision latitude (‘job strain‘) showed a high plaque prevalence odds, and a thicker IMT in the carotid bifurcation area compared with women in job situations with low demands and high decision latitude (‘relaxed’), even after adjustment for covariates. No such associations were seen in men. However, women in job situations with high psychological demands and high decision latitude (‘active’) also showed high odds for carotid plaque, and a thicker IMT in the carotid bifurcation, compared with women in ‘relaxed’ job situations. Thus, the specific hypothesis that high psychological job demands interact synergistically with low decision latitude in the development of carotid atherosclerosis could not be supported in this study, neither in men nor in women. Instead a more complex pattern of interaction between job demands and job decision latitude was shown.

Except for an association with smoking habits found in women, the associations between the four demand-control categories on the one hand, and behavioural and biological atherosclerotic risk factors, on the other, were weak and mostly not statistically significant. These results correspond well with findings in a review of 22 studies on work-related psychosocial factors and cardiovascular disease made by Theorell and Karasek, in which the authors concluded that the association between work-related psychosocial factors and cardiovascular risk factors has been more inconsistent compared with the association between work-related factors and cardiovascular disease.8

The actual differences in mean IMT in the CCA by work-related psychosocial factors were small among both men and women and may not be clinically important. Among women, similar findings were made in an earlier study regarding socioeconomic differences in IMT in the CCA.25 When analysing differences in IMT in the CCA in a population of middle-aged women known to have less wall thickening compared to men, non-atherosclerotic factors such as fibromuscular hypertrophy might play a larger role in the IMT measures than in men.20 This might particularly be true for the measurement of IMT in the CCA, where the atherosclerotic process starts later than in the bifurcation area.20 In our study there was no association found between presence of carotid plaque and carotid IMT in the CCA in women with a thinner IMT (below the mean value [0.73 mm]), while there was indeed such an association in women with a thicker IMT (above the mean value) (P < 0.001). Women with a thinner common carotid IMT showed no association with current smoking (P = 0.80) or with LDL cholesterol (P = 0.67), while there were strong associations in women with a thicker IMT (P < 0.001 and P < 0.001, respectively). Men with an IMT below as well as above the mean value (0.77 mm) showed a clear association with carotid plaque, (P = 0.002 and P = 0.001, respectively). Thus, the weaker associations found in women for IMT in the CCA as compared to measures in the bifurcation area, can perhaps be referred to a larger role of non-atherosclerotic factors in the IMT measurement in the CCA.

It has been questioned to what extent studies on work-related stress have recognized the possibility of a confounding effect on work environment characteristics stemming from socioeconomic status.13,32 In our study, both high psychological demands and high decision latitude were more prevalent in higher-level occupational status groups. On the other hand, those having manual jobs showed a relatively high prevalence of ‘passive’ job situations as well as job situations characterized by ‘job strain’. This was true both of men (26% and 33%, respectively) and women (35% and 35%, respectively). Adjustment for occupational status reduced the magnitude of the association between both ‘job strain’ and ‘passive’ job situation, and carotid plaque prevalence in women. However, this adjustment did not affect the high odds for atherosclerotic plaque among women in ‘active’ job situations. The effect of ‘job strain’ and ‘passive’ job situations on atherosclerosis might, therefore, be due to other factors associated with low occupational status than those accounted for in our analysis, and different explanations must be sought for the increased risk among women in ‘active’ job situations.

There are other theories of what constitutes adverse work-related psychosocial factors, such as the Effort Reward Imbalance (ERI) model introduced by Siegrist.33 This model focuses on the balance between efforts spent in the work situation on the one hand, and perceived rewards for this on the other hand, and an unfavourable imbalance has been found to predict cardiovascular disease.7 Unfortunately, we lack the opportunity to compare the predictive validity between the demand-control model and ERI in our study. However, the weak associations between job strain and preclinical atherosclerosis found in men in our study contrast with the findings from numerous previous studies with clinical cardiovascular disease outcomes and utilizing the same demand-control instrument, where the associations have been clearer and of similar magnitude for men and women.32

Job strain has been linked with both cardiovascular morbidity and mortality. However, according to the original hypothesis of Karasek, ‘active’ job situations characterized by high psychological demands and high decision latitude should be associated with relatively lower risk and with health-promoting activities.6 Nevertheless, job situations characterized by high psychological demands seem to have negative effects on women’s health, even when decision latitude is high. There may be explanations for the observed differences between men and women in the association between work-related psychosocial factors and atherosclerosis. First, there may be gender-specific differences in actual job situations. Recent data from Sweden indicate an increasing segregation of the Swedish labour market, in which working conditions have been improved in male-dominated, but not as much in female-dominated occupations. Among women, work-related psychological demands have increased, without a parallel increase in decision latitude.34 Besides these gender-based differences in the job situation, empirical data support the notion of a synergistically negative effect of unpaid domestic housework and paid work among women.35 In a recent Swedish study of men and women in high-status jobs, it was shown that women were additionally stressed by their large, unpaid domestic workload and greater responsibility for duties related to home and family. These women had higher stress-hormone levels during and after work than men at the same occupational level, reflecting the women’s greater burden.36

In a review by Schnall and Landsbergis,32 it was suggested that the job strain paradigm might be taken as a general model for social stress, with the combined effect of demands from home and family playing an important role. Because women in Swedish families are mainly responsible for children and the household, it is reasonable to assume that it is more difficult for them to handle overtime assignments in the workplace than is the case with men. It has been shown that women in occupations involving long working hours and overtime work have an increased risk of myocardial infarction. Conversely, overtime work actually seems to be a protective factor in men.1 In our study, women in ‘active’ job situations worked longer days than those with ‘relaxed’ job situations, and also reported doing more overtime. The same pattern was found among men. Men and women in job situations characterized by ‘job strain’ did not work longer days, but reported somewhat more overtime work than subjects in ‘relaxed’ job situations.

Another aspect of the work–family conflict refers to the presence of domestic stress such as household duties and child care. In our study, women in job situations characterized by high demands more often reported feeling stressed due to problems or demands arising outside the workplace (41% for those in an ‘active’ job situation and 43% for those in a job situation characterized by ‘job strain’, compared to 25% and 27% among women in a ‘passive’ and ‘relaxed’ job situation, respectively). Among women who were homemakers (not included in our study), the same level was 22%, pointing to a relatively greater general stress among women in high-demand occupations. Including the number of working hours, overtime work, and various measures of domestic stress in the regression models, only slightly reduced the magnitude of the initial associations between work-related psychosocial factors and carotid atherosclerosis. Perhaps these measures are too imprecise to capture the joint effects of domestic responsibilities and occupational demands, resulting in a situation wherein even the presence of high job decision latitude cannot prevent the strain resulting from an overload of psychological demands.

Methodological issues
Since we investigated only the vocationally active part of our population, there is the possibility of a health-related selection bias. However, the initial patterns showed no major change when we utilized information from the baseline questionnaire and included unemployed individuals and those on disability pensions in the analysis (n = 1065). Moreover, our study was performed on a community-based sample of the general population, which made it less sensitive to selection bias than samples based on workplace or clinical settings. Furthermore, there is no apparent reason to believe that preclinical atherosclerotic manifestations would influence a subject’s participation differentially with regard to psychosocial working conditions, since the outcome could be expected to be asymptomatic—particularly since all individuals with a history of cardiovascular disease were excluded from the analysis. Among those 480 subjects excluded, either due to incomplete laboratory test results, or because of an excessive time lag between their ultrasound, baseline, and laboratory examinations, there were slightly more men (47% versus 42%) than in the study population. However, the percentage of manual workers did not differ between the two groups, neither with regard to men (37.4% versus 38.6%) or women (35.7% versus 37.5%).

Psychosocial working conditions were self-assessed by questionnaire. Unlike cohort studies, cross-sectional studies recruit people that already have a disease. Thus, there is the potential that, due to their poor health, subjects may overemphasize unfavourable psychosocial exposures.37 However, since we investigated preclinical atherosclerosis, differential misclassification of psychosocial exposure due to cardiovascular symptoms does not seem to be a likely source of bias. We also considered the possibility of threshold effects between psychosocial exposures and outcome. Changing the cut-off for psychological demands and decision latitude did not affect the magnitude of the associations initially found. We also considered the possibility of changes in job position over time. However, in our sample, the mean length of time subjects spent in their current occupation was 19 years for women and 23 years for men, indicating that this measure was rather stable. Moreover, excluding subjects who reported job changes in the last 5 years did not alter the magnitude of the initial associations (data not shown).

In large populations, high-resolution B-mode ultrasonography has proven to be a valid, non-invasive method of monitoring atherosclerotic changes in the carotid arteries.20,21,24 It has been shown that the carotid IMT is associated with an increased risk of myocardial infarction in both men21,38 and women.38 Moreover, the presence of small or large plaques in the carotid bifurcation area has been shown to be associated with incident cardiovascular disease in men;21 the same is true of studies that include women (but not specifically separating women).39 During our study, the reproducibility of ultrasound results was monitored at regular intervals and found to be reasonably good.24,25 The sonographers had been given no information about a subject’s occupation or working conditions. Therefore, we regard B-mode ultrasonography as a valid and reliable measure of the extent of the general atherosclerotic process.

Conclusion

The specific hypothesis that a working situation characterized by high psychological demands and low decision latitude (‘job strain‘) is associated with increased carotid atherosclerosis could not be supported in this study, neither in men nor in women. Instead a more complex pattern of interaction between job demands and job decision latitude was shown. The patterns of associations between work-related factors and carotid atherosclerosis looked different in men and women. This might partly be due to gender-specific differences in actual job situations. Another explanation might involve the work–family conflict, even though, in our study, adjustment for domestic stress only slightly reduced the magnitude of the associations found in women.


KEY MESSAGES

  • The specific hypothesis that high job demands interact synergistically with low decision latitude (‘job strain’) in the development of carotid atherosclerosis could not be supported in this study, neither in men nor in women. Instead there was a more complex pattern of interaction between job demands and job decision latitude.
  • The patterns of associations between work-related factors and carotid atherosclerosis looked different in men and women.
  • The effect of work-related psychosocial factors on carotid atherosclerosis was only slightly attenuated after adjustment for established atherosclerotic risk factors, which suggests that other mediating factors may be of importance.

 

Acknowledgments

This study was made possible by grants from the Labor Market Insurance Company, the Swedish Council for Social Research (F 0289/1999), and the National Institute of Public Health, Sweden.

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