Occupational Medicine Advance Access originally published online on June 16, 2006
Occupational Medicine 2006 56(6):386-392; doi:10.1093/occmed/kql037
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Work-related life events, psychological well-being and cardiovascular risk factors in male Swedish automotive workers
Primary Health Care–Department of Primary Health Care, PO Box 5129, Göteborg SE-426 05, Sweden
Correspondence to: Gisela Rose, Primary Health Care, Salubritas AB, PO Box 5129, SE-426 05 V. Frölunda, Sweden. Tel: 46 705 123633; fax: 46 31 3399979; e-mail: gr{at}kungsportslakarna.se
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Abstract |
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Aims To analyse the relationship between life events, social support, psychological well-being and cardiovascular risk factors in blue- and white-collar Swedish automotive workers.
Methods Baseline questionnaire regarding life events, social support, depressed mood and mental strain and smoking habits. Follow-up questionnaire after 5 years included the Psychological General Well-being Inventory to assess various health variables. At baseline and follow-up, anthropometric data were obtained. Blood pressure, blood glucose and serum lipids were measured and smoking habits were surveyed.
Results The blue-collar workers showed a profile indicating increased cardiovascular risk with a higher proportion of smokers, a higher waist to hip ratio and higher triglycerides. They also reported themselves to have worse general health and less emotional self-control, but were less anxious than the white-collar workers. Negative life events, especially those related to work seemed to affect the well-being of the blue-collar workers more adversely than the white-collar workers. Being nervous and depressed at baseline increased the risk of poor psychological well-being at the follow-up. Social support within this 5-year perspective was a factor which predicted psychological well-being in both worker categories. Increase in cholesterol/high-density lipoprotein-cholesterol (HDL-C) ratio was the only cardiovascular risk factor associated with the strain of life events but not with work-related events.
Conclusion Over a 5-year period, men who experienced negative, strongly stressful and work-related life events displayed poorer psychological well-being at follow-up regardless of worker category. Social support was protective.
Keywords Coronary disease; life event; psychological; risk factors; stress
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Introduction |
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Workers of low occupational status are known to have a higher risk of cardiovascular disease than those of high status [1]. The pathways of increased risk in blue-collar workers as compared to white-collar workers are insufficiently known. Stressful life events, lack of social support and depression are thought to influence standard risk factor levels and thereby increase risk [2]. We examined whether these influences differed between blue- (manual) and white-collar (clerical) men at Volvo.
In the Volvo-Renault-Coeur study, we have previously demonstrated that stressful life events at work were associated with feelings of depression and mental strain [3]. The stressful events at work made up around one-third of all events and were mostly concerned with reorganizations and mergers in the workplace. The psychological reactions to strain at work were further associated with poorer health habits, which, however, differed between manual and clerical workers.
Blue-collar workers with mental strain and depression were more often smokers whereas white-collar workers who reported mental strain and depression on average consumed more alcohol. Thus, mental strain and depression seemed to be determinants of personal cardiovascular risk factors which vary according to socio-economic status.
In the present study, we examined whether a simple set of two questions about depression and mental strain could predict psychological well-being and cardiovascular risk over a 5-year follow-up period.
In this 5-year follow-up examination, we included the Psychological General Well-being Inventory (PGWB) which provided quantitative measures of six psychological dimensions: anxiety, depression, positive well-being, self-control, general health and vitality.
We hypothesized that stressful life events would predict poor psychological health and increased cardiovascular disease risk 5 years later. We also expected the association with cardiovascular risk factors to be stronger in the blue-collar workers than in the white-collar workers.
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Methods |
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In 1993, from the participating Volvo units, all Caucasian men born between 1 January 1943 and 1 January 1948 were extracted from the personnel files and sorted by last name in alphabetical order. From this cohort of
4000 men, every third person from the top of the list down was asked to participate in the study, until 1000 volunteers had been selected out of the 1144 men who were approached. The selected sample constituted about one-third of the corresponding age population of the plants involved. The participating Volvo entities were dominated by white-collar workers.
The sample size was determined in order to be able to detect a 20% difference of cardiovascular end-points after 10 years in Swedish men compared to a corresponding French cohort with 90% probability. This report pertains to the Swedish cohort only.
Information on personal history of illness, family status, workers category (blue- and white-collar), work and lifestyle factors including exercise, smoking and alcohol habits was collected. Measurements of mood, mental strain, social support and life events were also recorded [3,4].
Based on our previous work, social support was defined and summarized as a composite index of seven questions, which were assigned score points (p):
- (i) Ever engaged in social leisure activities? Yes = 1p
- (ii) Social leisure activities every week? Yes = 1p
- (iii) Engaged in hobbies, one or more? Yes = 1p
- (iv) Belongs to an association? Yes = 1p
- (v) Number of close friends? 0 friends = 0p; 1–2 friends = 1p; 3–5 friends = 2p; >5 friends = 3p
- (vi) Meets friends every week? Yes = 1p
- (vii) Meets with friends every month? Yes = 1p
- (ii) Social leisure activities every week? Yes = 1p
The analysis compares those with events and those without corresponding events.
In 1993, the following questions about mood and mental strain were asked: ‘How often do you feel unhappy, depressed and sad?’ and ‘How often do you feel fidgety, nervous and tense?’ These two questions with nine continuous alternatives ranging from never to always were used for the analyses of the follow-up data [5].
Determination of blood pressure (BP), weight, height, circumferences of waist and hip, fasting serum concentrations of cholesterol, HDL-C, triglycerides and blood glucose were collected using methods detailed in a previous report [3].
In 1998, health professionals contacted the men who participated in 1993. To locate addresses and telephone numbers, company personnel records and the national person number identification system were used. All individuals were contacted by mail and/or telephone and invited for an interview, lasting 45–60 min, and examination by a nurse. The Volvo team was able to follow up 954 subjects (95%). Reasons for non-participation are shown in Table 1 (available as Supplementary data at Occupational Medicine Online).
The health examination in 1998 included the following measurements: weight, height, BP, circumferences of waist and hip, fasting serum concentrations of cholesterol, HDL-C, triglycerides and blood glucose.
Body mass index (BMI) was calculated as weight (kg) divided by height square (m2). Waist to hip ratio (WHR) was calculated as waist circumference (cm) divided by hip circumference (cm).
Smoking habits were also surveyed.
Methods of standardization, collection and analyses followed those of the baseline study with venous blood tests collected after an overnight's fasting. BP was measured in the supine position as the average of three measurements taken from the right arm after a 10-min rest, using a semi-automatic cuff (LIC Hygien, Solna and D2 International, Hestia Pharm, Mannheim, Germany). The laboratory methods have been previously described [6].
The PGWB was completed at the follow-up visit. It has been tested for validity and reliability and has been used in many studies [7]. The PGWB index included six subscales for assessment of anxiety, depressed mood, positive well-being, self-control, general health and vitality. The subscales had three to five items each. Each item had six response options that were scored on a scale from 1 to 6. The scores of the PGWB index ranged from 22 to 132. The subscales ranged from 1 to 18, 24 or 30. Low scores reflected states of distress and high scores excellent well-being. Self-control refers to the question: ‘How well are you in control over your feelings, thoughts and actions?’
For univariate comparisons between white-collar and blue-collar workers with regard to PGWB scores, lifestyle variables and somatic variables, two sample t-tests were performed.
Multivariate linear regressions were fitted to test the associations between PGWB variables and life event variables. Table 2 (available as Supplementary data at Occupational Medicine Online) shows the variable definitions, abbreviations, types and values used.
Each model used one of the seven PGWB variables as the dependent (outcome) variable and one of the four life event variables as an independent (explanatory) variable. Multivariate logistic regressions were fitted to test the associations between cardiovascular disease risk variables and life event variables. Each model used one of the eight cardiovascular disease risk variables as the dependent (outcome) variable and one of the four life event variables as an independent (explanatory) variable. To avoid potential collinearity, only one life event variable was entered into any model at the same time. It was pre-determined that each model should be adjusted for age, work type and all three baseline psychological variables. Other demographic or occupational variables such as marital status, education or job satisfaction were entered into models if they significantly improved model fitting or were statistically significant. Interaction between independent variables, such as interaction between work type and age or work type and education, were added into models only if the interaction variable was statistically significant.
To investigate the association between life event variables and change in cardiovascular disease risk profile, multivariate logistic regressions were performed, using worsening of risk factors as dependent variables (1 worsened, 0 otherwise, see definitions in Table 2) and life event variables as independent variables, adjusting for demographics and occupational variables. Potential interactions were considered and tested but only statistically significant interactions would be reported in the text.
All analyses were performed with STATA 8.0 package.
This 5-year follow-up investigation was a part of the 10-year study which was approved by the Ethics Committee of Gothenburg University on 11 February 1993.
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Results |
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Of the 954 subjects followed up from the original study, complete data were available for 926 subjects in the follow-up study.
As shown in Table 3, there are several differences between blue- and white-collar workers at the time of the follow-up examination. Blue-collar workers reported less anxiety, less self-control and worse general health. They had higher WHR, higher triglycerides, and were more often smokers than white-collar workers. PGWB scores as outcome are shown in Table 3.
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Strongly stressful life events were significantly negatively associated with the vitality score. Workers who experienced strongly stressful life events at baseline scored on average 0.6 score points lower on the vitality score at follow-up than workers who did not (P < 0.05). Work-related life events were found to be significantly associated with anxiety and general health at follow-up. Workers who experienced work-related life events on average had lower scores in these assessments than workers who did not (P < 0.05). These associations were not modified by work type, i.e. the negative effects of strongly stressful life events and work-related life events on PGWB scores, if any, were the same among blue-collar workers and white-collar workers. Negative life events were significantly associated with self-control and this association was modified by work type. Among blue-collar workers, those who experienced negative life events at baseline on average scored 0.6 points lower on the self-control score at follow-up than those who did not (P < 0.01). However, among white-collar workers, experiencing negative life events at baseline was associated with only a 0.1 point lower average score (P < 0.01), i.e. the negative effect of experiencing negative life events on self-control was not as strong among white-collar workers as it was among blue-collar workers. Positive life events were not found to be associated with any of the PGWB scores at follow-up.
Work type was found to be significantly associated with each of the PGWB variables (PGWB1 – PGWB6 and PGWB total score), after adjusting for other variables. White-collar workers on average had lower anxiety scores and higher general health scores than blue-collar workers at follow-up (P < 0.05 and P < 0.001, respectively). No interaction between work type and other variables was found in these two assessments. In assessments where interaction between work type and other variables were found significant, work type took its effects by modifying the effects of other variables on the PGWB scores. For example, university education was found to be significantly associated with the PGWB score of positive well-being, and its effects were modified by work type. Among blue-collar workers, those who had a university degree on average scored 2.1 points higher than those who did not (P < 0.05). However, among white-collar workers, those who had a university education on average scored 0.4 points lower than those who did not (P < 0.01, see footnote ‘d’ in Table 4). Detailed statistics are reported in Table 4. Since interactions between white- or blue-collar work and other demographic variables were not the primary focus of this paper, they are not discussed in the text here. Subjects who were single at baseline on average had lower scores (regression coefficient –1.0, P < 0.01) in positive well-being at follow-up than those who were married. This effect was not modified by any other variables.
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There were three assessments of psychological well-being at baseline. All of them were found to be significantly associated with the PGWB scores at follow-up after adjusting for other variables except for social support, which did not reach statistical significance in models with anxiety, self-control and general health. On average, subjects who had higher scores in questions about being nervous and being depressed at baseline had significantly lower scores for every PGWB assessment than those who had lower scores in these two questions. On the other hand, subjects who had higher scores in the question about social support at baseline had significantly higher scores in some PGWB assessments. No interaction between baseline psychological variables and work type was found.
When the relationship between changes of cardiovascular disease risk profiles and life event were investigated, no significant association was found for changes in BMI, WHR or cholesterol level (CHO) (see Table 5).
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The only association between changes of risk profile and life events was present between changes in cholesterol-HDL ratio (CHR) and experiencing a strongly stressful life event. Workers who experienced strongly stressful life events at baseline were more likely to have increased the CHR over the period between baseline and follow-up than workers who did not (OR 1.72, P < 0.05). No interaction between strongly stressful life events and other variables was found.
Being single at baseline was found to be associated with changes in BMI, WHR and CHO. Workers who were single at baseline were more likely to have developed obesity (BMI > 30), hypercholesteremia and increased WHR over the period between baseline and follow-up than workers who were married at baseline (OR 2.04, 2.28 and 1.81, respectively, P < 0.05 in all cases).
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Discussion |
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In the 5-year follow-up investigation of 1000 workers at Volvo, Sweden, we found increased cardiovascular risk in blue-collar compared to white-collar workers. Blue-collar workers were more often smokers, had higher WHR and higher triglycerides. Partially confirming what has been reported in other studies, Volvo blue-collar workers on average reported slightly worse general health and lower self-control, but less anxiety than did white-collar workers [8–10].
During the 1990s, the Volvo Company was successful in implementing a strongly decentralized organization [11]. Certain tasks were delegated to blue-collar work groups such as increased responsibility for planning and coordination which resulted in a more varied work content and greater overall responsibility. This situation may not help to explain the worse health experienced by the blue-collar workers as described in other studies [12].
Although not clearly understood is why workers who experienced a strongly stressful life event at baseline were more likely to increase their cholesterol/HDL-C ratio. No change of a biological cardiovascular risk factor was seen as a consequence of work-related life events.
In the current study, experience of negative life events was significantly negatively associated with self-control and this association was modified by work type, with a stronger effect in blue-collar workers. Aro and Hasan [8] suggested that psychosocial stress is mostly related to indicators of morbidity such as perceived health, bodily symptoms and sickness behaviour.
Furthermore, social support seemed to be a factor which protected, over 5 years, against decreasing psychological well-being in both blue- and white-collar workers. The preventive effect of good social support has been shown in many studies [13–18].
In 1993, 56% of blue-collar workers and 66% of white-collar workers were exposed to negative life events. Of those, about one-third were work-related life events (mostly mergers and organizational changes). As found in this and other studies, stressful and strongly stressful life events seemed to have lasting consequences in a 5-year perspective [19]. Strongly stressful events were negatively associated with vitality, negative life events with lower self-control, and work-related events predicted lower general health and anxiety at follow-up independent of type of work. There are few studies which have investigated the impact of work-related life events on health [20]. Tennant [21] showed psychological disorders, especially depression, to be increasingly caused by work-related stressors.
In another Swedish study, job–stress factors were not related to coronary risk factors [22]. We suggest that consideration should be given to intensified psychological support during changes of working conditions so as to prevent adverse health effects.
A highly significant interrelationship was seen between two simple questions ‘How often do you feel unhappy, depressed and sad?’ and ‘How often do you feel fidgety, nervous or tense?’ used at baseline and a corresponding group of questions in the PGWB used 5 years later. This may indicate that these complaints are stable over time, and that occupational health staff can estimate the psychological status of the employees without time-consuming questionnaires.
In addition to our findings, the high compliance due to the occupational health setting, the width of data collected and the long-term follow-up add to the strength of this study. While the focus on middle-age men was necessary from a cardiovascular end-point perspective, not including women is a weakness. As shown in a previous study of Swedish women, low socio-economic status, as assessed by low occupational level, was associated with increased cardiovascular risk and explained by lack of self-control in low status women [23].
In conclusion, when measuring traditional risk factors for cardiovascular disease, it seems justified to stress the importance of dimensions of psychological well-being and to integrate somatic, social and psychological aspects into a common concept of work-related distress [24–30].
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Conflicts of interest |
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None declared.
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Acknowledgements |
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The baseline investigations at Volvo were performed by Siv Thornell, Lisbeth Paffrath and Pia Johannisson. The third step interviews were conducted by Siv Thornell, Annie Jansson, Caroline Karlsson, Inga-Greta Wittlöv and Pia Lindén. Sandra Ross assisted with the language revision.
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