a National Institute of Public Health and the Environment, Bilthoven, The Netherlands.
b MRC Biostatistics Unit, Institute of Public Health, University of Cambridge, UK.
c Department of Psychiatry, University of Groningen, The Netherlands.
Reprint requests to: AJM van Loon, National Institute of Public Health and the Environment, Department of Chronic Disease Epidemiology, PO Box 1, 3720 BA Bilthoven, The Netherlands. E-mail: jeanne.van.loon{at}rivm.nl
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Abstract |
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Methods Cross-sectional data obtained from 3309 respondents participating in an ongoing prospective cohort study in the Netherlands on psychosocial factors and cancer risk were used to study the association between psychosocial job characteristics and lifestyle. Information on job characteristics and risk factor prevalence was collected from 2065-year-old men and women, through self-administered questionnaires. Multiple logistic and linear regression analyses were undertaken by gender, with adjustment for age and education.
Results No differences in the prevalence of lifestyle risk factors for cancer were found amongst the psychosocial work characteristics studied. Moreover, little evidence was found for a relation between job (or iso-) strain and cancer-related lifestyles in multivariate analyses.
Conclusions The present study found no support for the hypothesis that job strain or iso-strain are associated with a cancer-related lifestyle. Further research on the role of other psychosocial factorslike personality or social support outside workin mediating associations between job characteristics and lifestyle, is warranted.
Keywords Job stress, demand-control theory, smoking, alcohol, diet, physical activity
Accepted 26 January 2000
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Introduction |
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Associations between job strain and health behaviour may vary by sex.12,13,16 Therefore we have conducted the analyses for men and women separately.
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Methods |
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Psychosocial work factors
Information on work characteristics was obtained by the Health and Life Experiences Questionnaire (HLEQ) as part of a broader range of assessments. The instrument was designed for initial use in the European Prospective Investigation into Cancer and Nutrition (EPIC) study in Norfolk, UK. A more detailed outline of aspects of the HLEQ assessment approach has been provided elsewhere.19 As for most measures, validated Dutch equivalents were not present, but the English version of the questionnaire was translated into Dutch (by one person) and back-translated into English (by another person). Differences in nuance between the original and the back-translated version were resolved by the researchers involved in the project.
In this paper we focus on three constructs representative of the often used job strain model of Karasek,1 namely job demands, job control and job support, with item choice based on scales used in the Whitehall II study.20 The separate constructs were measured respectively through 4-item, 14-item and 5-item scales (Appendix). Response categories ranged from 1 (often) to 5 (never). First, all items were recoded in the same direction, whereby high scores represent more demands, more control or more support. Next, for those with no more than one missing item in a scale, scale total scores were calculated. For those respondents with one missing item, the mean score of the remaining items was added to the total score of all completed items. The response category not applicable (added for seven items on the role of supervisors and colleagues) was given the score of the middle category. A summary score for job control was computed by weighting scores on decision authority (eight items) and skill discretion (six items) equally. Finally, two combined variables were constructed: job strain and iso-strain. Job strain was defined as having simultaneously high job demands (above the median score) and low job control (below the median). Low strain jobs are defined as having low demands and high control; in active jobs people were supposed to have high demands and high control and in passive jobs people have low demands as well as low control (Figure 1). For the definition of iso-strain, social support at work was combined with job strain to create eight exposure groups (Figure 1
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Statistical methods
The prevalence of lifestyle risk factors for cancer was compared within categories of job demands, job control and job support (dichotomized by the median value), for men and women separately. Multiple logistic regression analysis was used to study the association between job strain or iso-strain (independent, categorical variables) and the probability of having a specific lifestyle. Smoking was dichotomized as ever versus never smoking and as current smoking versus no smoking. Alcohol consumption was dichotomized as current alcohol intake versus no alcohol intake and as alcohol intake above the median versus intake below the median (for the latter abstainers were excluded). Intake of fruit and vegetables was dichotomized by the median value, for men and women separately. Physical activity was dichotomized as low versus medium plus high. Furthermore, linear regression analysis was used to study the association between job strain or iso-strain and the amount of cigarettes smoked (for current smokers), the number of alcoholic beverages per day (for current drinkers) and the number of servings per day for fruit and vegetable intake. In the logistic and linear regression models adjustment was made for age (continuous) and highest level of education (low, medium, high). Because it is not clear which job strain category is most beneficial with regard to healthy lifestyles, high strain was used as comparison group in the job strain models and high strain combined with low support as the comparison group in the iso-strain models. Statistical analyses were carried out using SAS, version 6.12.
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Results |
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Results from linear regression analyses (not presented) were comparable with findings from logistic regression analyses: no statistically significant associations were found between job strain and smoking (number of cigarettes), alcohol intake (glasses per day) or intake of fruit and vegetables (servings per day). With regard to iso-strain, statistically significant associations were found for number of cigarettes smoked and alcohol intake, among women. However, the parameter estimate for the number of cigarettes smoked per day was only significantly different in the low strain-low support category (B = 3.05, SE 1.55, P < 0.05) compared with the high strain-low support category. The same was found for number of alcoholic drinks per day (low strain-low support B = 0.37, SE 0.11, P < 0.05).
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Discussion |
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Other studies on job characteristics and lifestyle focused mainly on smoking habits and alcohol consumption, due to the fact that in most studies established risk factors for cardiovascular disease were considered. Studies on smoking and job characteristics showed inconsistent results. In general, hardly any significant association was found for job demands or job support and smoking status or number of cigarettes smoked per day.12,13,15,16,24,25 In some studies low job control was found to be associated with higher prevalence of current smoking among men2426 or number of cigarettes smoked per day.13 However, in several other studies no significant associations were reported between job control and smoking status12,15,16 or number of cigarettes smoked.15,27 Although the measurement of job characteristics differs between these studies (based on job title by imputation or based on questionnaire information), this is not the reason for inconsistencies in the results. When considering the association between job strain and smoking, there is more evidence for an association between job strain and number of cigarettes smoked,11,13,17,28 than for job strain and smoking status.10 However, in most studies no significant associations are reported.9,12,16,24,25,27,29
In two studies on alcohol intake (g/day) and job demands, job control or job support12,27 no statistically significant associations were found. When considering job strain in relation to alcohol intake,9,11,12,17,27 two studies reported a statistically significant inverse association.11,12
Most studies concerning lack of physical activity and job characteristics gave no support for an association. Three studies reported no significant association,9,17,27 while in one study a positive association was reported for women.10 However, in the latter a proxy for job strain (employment outside the home) was used.
Only one study considered the association between healthy eating and job demands.15 Healthy eating was measured by means of the consumption of fruit, vegetables, whole foods and fish. No significant associations were reported.
No studies on the association between iso-strain and lifestyle were found.
Although there are differences in response rates, study population, or measurement of job characteristics between these studies, there are no clear differences in these factors between studies where significant associations are reported compared with studies where no significant associations are found. Nevertheless, response rates, choice of study population or measurement of job characteristics may affect the validity of the results.
The response rate for the MORGEN-project was 50% in 1993 and 44% in 1996. For the questionnaire on psychosocial factors, the response rate was 55%. Therefore, our data may have been affected by selection bias. A small non-response survey among the MORGEN-study population conducted in 1993,30 showed that men and people with a lower level of education are possibly under-represented in MORGEN, whereas non-smokers, sportsmen and people with less-than-good self-reported health are over-represented. Bias in the associations between psychosocial job characteristics and cancer-related lifestyles would only occur when response status is associated with both job characteristics and lifestyles. It seems unlikely that people with cancer-related lifestyles would respond in a different way compared with people without cancer-related lifestyles according to their psychosocial work environment. In our study on psychosocial factors and cancer risk, response rates were also lower among people with a lower level of education. Because in general, people with higher socioeconomic status (SES) have higher levels of job demand and job control,31 these differences in response rates among SES groups may lead to higher mean scores for job demand and job control. However, the prevalence of job strain did not substantially differ between SES groups in our study population (not presented).
We restricted the study population to those who had a paid job at the time they completed the questionnaire. Therefore, the findings are restricted to relatively healthy employed workers, because those who might have already left the labour force as a result of the adverse health effects of work-related exposures (e.g. strain) are excluded. In the MORGEN data from 1993 and 1996, 77% of the men and 51% of the women had a paid job. The corresponding percentages in the sub-population who responded to the questionnaire on psychosocial factors were 80% and 62%. We compared the prevalence of the established lifestyle risk factors for cancer among those with and without a paid job in the MORGEN population of 1993 and 1996. There were no striking differences in cancer-related lifestyles between women with and without a paid job but current smoking was more prevalent among men without a paid job and the mean alcohol intake (for current drinkers) was also higher in this group (data not presented). Consequently, our findings refer mainly to the active labour force instead of the general population.
In this study the assessment of psychosocial work characteristics was based on self-report. Self-reports may provide inaccurate descriptions of job characteristics, or may be biased by personality traits such as negative affectivity.4 Nonetheless, information derived from an objective classification based on job title neglects within-occupation variance and it assumes that conflicting demands, time pressure and lack of control will be just as stressful for all people. Thus, an imputation procedure has less power than a method based on individual level scores in which variance due to both person and occupation exists.26
We used cross-sectional data from an ongoing prospective study on psychosocial factors and cancer risk. The classification of subjects with regard to the job variables was based on the current job, and all of the behaviours may have preceded the initiation of the current job. Therefore, associations between job characteristics and lifestyle might be interpreted as lifestyle preservation, rather than lifestyle initiation. Today's exposure to job strain is not a valid indicator for lifetime exposure, since employees change jobs, gain new skills and so on. Misclassification and a smaller effect size might be the consequence.4
Finally, it may be possible that other psychosocial factors, such as personality or social support outside work, may mediate the associations between job characteristics and lifestyle. Therefore, the role of social support (not work related) and personality characteristics needs to be explored in future work.
In conclusion, we found no association between job strain or iso-strain and cancer-related lifestyles but because other studies on job strain and lifestyles showed inconsistent results, the lifestyle risk factors for cancer will be considered in further research on job strain and cancer risk.
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Appendix |
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Job demands
This subscale consisted of four items:
Job control
Eight items considered decision authority, namely:
The six items for skill discretion were:
Social support
The five items for social support were:
The construction of these subscales was based on results from the Whitehall-II study20 and in our data this structure was confirmed by means of factor analysis.
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Acknowledgments |
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References |
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