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Prevalent cardiovascular disease, risk factors and selection out of shift work
Mika Kivimäki1, Marianna Virtanen, Marko Elovainio
1Finnish Institute of Occupational Health, Topeliuksenkatu 41 a A, FIN-00250 Helsinki, Finland. mika.kivimaki@ttl.fi
Insights
Health issues cause employees with multiple risk factors to leave jobs, irrespective of work schedule. This suggests health-related selection bias is unlikely to significantly impact studies on shift work and cardiovascular disease (CVD).
Area of Science:
- Occupational Health
- Epidemiology
- Cardiovascular Disease Research
Background:
- Shift work is a known occupational exposure.
- Previous research suggests a link between shift work and cardiovascular disease (CVD).
- Potential bias from health-related attrition in shift work studies needs investigation.
Purpose of the Study:
- To investigate if health-related factors influence workers leaving shift work positions.
- To determine if this selection-out process biases the observed association between shift work and cardiovascular disease (CVD).
Main Methods:
- A cohort of 7037 female nurses in Finland was studied (2000-2004).
- Data included doctor-diagnosed CVD and risk factors (hypertension, high cholesterol, obesity, diabetes).
- Workplace departure and shift-to-day work changes were tracked.
Main Results:
- Nurses with diabetes or multiple CVD risk factors were more likely to leave their jobs.
- This association was observed regardless of whether they worked shifts or days.
- Prevalent CVD and risk factors did not predict a change from shift to day work.
Conclusions:
- Workers with multiple health risk factors tend to leave their jobs, independent of work schedule.
- Health-related selection out of shift work is unlikely to be a major source of bias in CVD research.
- Findings suggest the association between shift work and CVD is less likely to be confounded by self-selection based on health status.
Objectives:
This study examines whether health-related selection out of shift work is likely to bias the association between shift work and cardiovascular disease (CVD).
Methods:
Survey data on doctor-diagnosed CVD (myocardial infarction, angina, or hypertension) and risk factors (high blood pressure, high cholesterol concentration, obesity, and diabetes) were collected in 2000-2002 for a cohort of 7037 female nurses (5038 shift workers, 1999 day workers) in 21 Finnish hospitals. The follow-up in 2004 determined those who had left their workplace or changed from shift work to day work.
Results:
Among the shift workers, the age-adjusted odds for leaving the organization was 1.83 (95% CI 1.01-3.32) times higher for those with prevalent diabetes and 2.21 (95% CI 1.12-4.39) times higher for those with three to four risk factors than for their counterparts with no diabetes or risk factors. The associations between CVD risk factors and leaving the organization were similar for the day workers. The prevalent CVD and risk factors did not predict a change to day work among the shift workers who remained in the organization during the entire follow-up period.
Conclusions:
Employees with several risk factors are more likely to leave an organization regardless of the type of work schedule. Health-related selection out of shift work is an unlikely source of major bias in research on shift work and CVD.
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