Fig. 1.

Associations of the number of 24-h shifts in the past month with systolic blood pressure (a) and diastolic blood pressure (b) in 295 male firefighters who worked at fire stations and were not taking anti-hypertensive medication (the reference group: 8–11 shifts). The black bars indicate the results from the univariate analysis, and the white bars indicate the results from the multivariate analysis after controlling for age, education, more demanding job over the past years, and body mass index. *p < 0.05 and **p < 0.01