A longitudinal study on the relationship between shift work and the progression of hypertension in male Japanese workers.

Objective: In this 1991-2001 cohort study of 6495 male workers in a Japanese steel company, we investigated whether shift work affects progression from mild hypertension to severe hypertension.

Design: A prospective cohort study.

Participants: Participants had mild hypertension at entry into the study with systolic blood pressure of 140-159 mmHg or diastolic blood pressure of 90-99 mmHg or both before treatment. In summary, 2911-2941 workers were included for each endpoint. Pooled logistic regression analysis was performed to adjust for the effect of contributing factors and annual variations.

Main Outcome: Either severe hypertension (systolic blood pressure >or= 160 mmHg and/or diastolic blood pressure >or= 100 mmHg), severe systolic hypertension (systolic blood pressure >or= 160 mmHg) or severe diastolic hypertension (diastolic blood pressure >or= 100 mmHg) was defined as a different endpoint of observation.

Results: Job schedule was significantly associated with progression from mild hypertension to severe hypertension and severe diastolic hypertension. The odds ratios of shift workers compared with regular day workers were 1.23 (95% confidence interval: 1.05-1.44) and 1.28 (95% confidence interval: 1.07-1.52) for severe hypertension and severe diastolic hypertension, respectively. Age, body mass index, creatinine, gamma-glutamyl transpeptidase, and glycosylated hemoglobin A1c were also significantly associated with severe hypertension, severe systolic hypertension and severe diastolic hypertension.

Conclusion: Our study revealed that shift work is a significant and independent risk factor for the progression of hypertension.