Retrospective Cohort Study of the Risk of Hypertension among Shift Workers

Kubo, Tatsuhiko

Monday, March 19, 2012: 17:20

Isla Mujeres 2 (Cancun Center)

Tatsuhiko Kubo, Department of Public Heatlh, University Of Occupational And Environmental Health, Kitakyushu, Japan

Ichiro Oyama, Corporate ESH & QA, Asahi Kasei Corporation, Tokyo, Japan

Kiyoshi Kidouchi, Health Care Center, Asahi Kasei Corporation Nobeoka Office, Nobeoka, Japan

Masamizu Kunimoto, Health Care Center, Asahi Kasei Corporation Nobeoka Office, Nobeoka, Japan

Kiyoyumi Shirane, Health Care Center, Asahi Kasei Corporation Nobeoka Office, Nobeoka, Japan

Hidetoshi Tabata, Health Care Center, Asahi Kasei Corporation Nobeoka Office, Nobeoka, Japan

Zenzaburo Ishihara, Health Care Center, Asahi Kasei Nobeoka Office, Nobeoka, Japan

Ken Sabanai, Health Care Center, Asahi Kasei Nobeoka Office, Nobeoka, Japan

Takehiro Nakamura, Health Care Center, Asahi Kasei Chemicals Corporation Mizushima Works, Mizushima, Japan

Introduction
Epidemiological studies on shift work face difficulties regarding work schedule follow-up, potential significant result bias due to the healthy worker effect and confounding by socioeconomic factors. To overcome these issues, we established a retrospective cohort study with unique strengths and investigated the effect of shift working on risk of hypertension.

Methods
The study was designed as retrospective cohort study, which was established based on a health care database system belonging to a manufacturing corporation in Japan. The study database contains data regarding annual health check-ups and work schedules for every worker in Japan since 1981.Subjects for this study were 10,173 male employees (9,209 daytime workers and 964 three shift workers; mean age 23.7 years) whose work schedules were consistent during the follow-up period. Subjects with Systolic blood pressure >=140mmHg or diastolic blood pressure >=90mmHg were treated as cases for hypertension. The Cox proportional hazards model was used to estimate the risk, with adjustments for age, smoking, alcohol drinking, and leisure time physical activity and body mass index (BMI).

Results
During the 27.5 years of follow up (129,194 person-years in total; mean follow-up period = 12.3 years), 3,386 incidences of hypertension were detected. Cox proportional-hazards model analysis revealed significantly increased risk among three shift workers(relative risk (RR) =1.95, 95% Confidence interval (CI): 1.78, 2.15, p<0.001).

Discussion
Risk of hypertension among male shift workers was statistically demonstrated. Our study’s design is superior to that of previous studies in several aspects. First, we were able to obtain very good quality exposure information. Second, the cohort study design may have reduced the influence of the healthy worker effect to some extent. Third, since all study subjects belonged to the same company, socioeconomic differences are believed to have had relatively little effect on the results.

A2130 Retrospective Cohort Study of the Risk of Hypertension among Shift Workers