Objective: Night shift work is associated with ischemic cardiovascular disorders. It is not currently known whether it may be causally linked to the metabolic syndrome (MS), a risk condition for ischemic cardiovascular disorders. The syndrome is given by the presence, in the same individual, of visceral obesity associated with even mild alterations in glucidic and lipidic homeostasis, and in blood pressure. Aim of this study was to assess whether a causal relationship exists between night shift work and the development of MS.
Methods: Male and female nurses performing night shifts, free from any component of MS at baseline, were evaluated annually for the development of the disorder during a four-year follow-up. Male and female nurses performing daytime work only, visited during the same time period, represented the control group.
Results: The cumulative incidence of MS was 9.0% (36 out of 402) among night shift workers, and 1.8% (6 out of 336) among day-time workers (Relative Risk-R.R.-: 5.0, 95% Confidence Intervals-C.I.- 2.1 to 14.6). The annual rate of incidence of MS was 2.9% in night-shift workers and 0.5% in day-time workers. Kaplan-Meier survival curves of the two groups were significantly different (Log Rank test; p<0.001). Multiple Cox regression analysis (forward selection method based on likelihood ratio) showed that among selected variables (age, gender, smoking, alcohol intake, familiar history, physical activity, and work schedule) the only predictors of occurrence of MS were sedentariness (Hazard Ratio-HR-=2.92; 95% CI=1.64 to 5.18; p=0.017), and night shift work (HR=5.10; 95% CI=2.15 to 12.11; p<0.001).
Conclusions: the risk of developing MS is strongly associated with night shift work in nurses. Medical counseling should be promptly instituted in night shift workers with the syndrome, and in case of persistance or progression, a change in work schedule should be considered.
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