Long overtime working and the risk of occupational hypertension

Background Hypertension is an important occupational risk factor for adults and associated with the working type and working hours. Objective We aimed to determine the association between overtime work hours per month (OWHs) and the risk of developing occupational hypertension. Subjects and methods We studied 1504 employees of two public institutions, who were providing electricity service to the general population on Kansai area in Japan. The age ranged from 23 to 62 years (mean 39.8±4.0 ) and 86.4 % of the cohort were men. OWHs were calculated from the attendance management system. OWHS were grouped into the following categories; less than 50 hours, 50 to 69 hours, more than 70 hours per month. Subjects were analyzed by body mass index, blood pressure, blood chemistry, and sleeping times according to annual health check-up data. And, workplace clinic blood pressure was taken at rest during the Industrial physician interview due to overtime work. Diagnosis of hypertension was based on systolic blood pressure (SBP) ≧140 and/or diastolic blood pressure (DBP) ≧90mmHg, according to the Janese Society of Hypertension guidelines. Results The mean value of OWTs in this study subjects were 44.4±11.6 hours. The mean value of SBP and DBP at workplace clinic of subjects with more than 50 hours OWHs, were significantly elevated to subjects with less than 50 hours OWHs (126±15.1 mmHg vs 114.8±12.6 mmHg; p<0.0001 and 80.5±12.1mmHg vs 71.8±9.9mmHg; p<0.0001, respectively. HR:1.64, 65%CI: 1.02-2.53). The mean value of SBP at workplace clinic of subjects with more than 70 hours OWHs were more elevated compared to subjects with 50 to 69 hours OWHs (132.4±13.5 mmHg vs 122.9±14.9 mmHg; p<0.0014, HR: 1.42, 95%CI: 1.14-2.01). Among employees aged less than 35years, there were no significant differences of both SBP and DBP under more than 50 hours OWHs (114.8±12.6 mmHg vs 115.1±10.0 mmHg; p=ns).The mean values of SBP and DBP at annual health check-up have not significantly differentiated between subjects with less than 50 hours and more than 50 hours OWHs (114.8 ±12.6 mmHg vs 114.9±13.3 mmHg; p=ns and 7.9±10.2 mmHg vs 71.9±10.2mmHg; p=ns, respectively). Conclusion Long OWHs were an important risk factor of occupational hypertension among employees aged more than 35 years, which could not be detected at annual health check-up. Workplace strategies targeting long OWHs could be effective in reducing the clinical health burden of occupational hypertension.