Cardiovascular Risk Factors and Primary Selection into Shift Work

Objectives This study examined differences between future shift workers and future day workers as regards cardiovascular risk factors before they began different work schedules and the differences that remained after control for sociodemographic factors and general self-efficacy. Methods Altogether 2870 newly educated social and health care workers filled out a questionnaire a few weeks before finishing their formal training and again 1 year after graduation. They answered questions on diabetes, hypertension, lifestyle habits, sociodemographic factors, and general self-efficacy. Results In the unadjusted analyses, baseline obesity was associated with fixed evening work at follow-up. Minimal or light-to-moderate leisure-time physical activity was associated with a decrease in the odds ratio (OR) for two or three shifts including night work. Smoking status was associated with fixed evening work, fixed night work, and two-or three-shift work including night work. After adjustment for sociodemographic factors and general self-efficacy, smoking was prospectively associated with fixed evening work [OR 1.56, 95% confidence interval (95% CI) 1.21-2.02] and fixed night work (OR 1.64,95% CI 1.04-2.56). Being an ex-smoker was associated with two-or three-shift work including night work (OR 1.85, 95% CI 1.28-2.68). The association between two-and three-shift work and smoking was only of borderline significance (OR 1.37, 95% CI 1.00-1.87). Conclusions Compared with future day workers, fixed evening or fixed night workers already smoked more before they began shift work. Being an ex-smoker was significantly associated with two-or three-shift work including night work. These results indicate that smoking status should not solely be treated as a mediator between some variants of shiftwork schedules and cardiovascular diseases but should also be considered a confounder.