Retrospective cohort study of the risk of obesity among shift workers: findings from the Industry-based Shift Workers' Health study, Japan.
OBJECTIVE
The authors investigated the effect of shift working on the risk of obesity using data from the Industry-based Shift Workers' Health (IbSH) study, a retrospective cohort study based on a health care database system belonging to a manufacturing corporation in Japan.


METHODS
The study database contains data on annual health check-ups and work schedules for every worker in the corporation in Japan since 1981. Study subjects consisted of 9912 male employees (8892 daytime workers and 920 rotating three-shift workers; mean age at first check-up was 23.7 years) whose work schedules were consistent during the follow-up period. Obesity was defined as a body mass index ≥ 25.0.


RESULTS
3319 cases of obesity were recorded over the 27.5 years of retrospective follow-up. Kaplan-Meier survival analysis visually demonstrated an increased risk of obesity among shift workers. The risk becomes particularly obvious after 10 years of follow-up. Cox proportional-hazards model analysis revealed a significantly increased risk among shift workers (RR 1.14, 95% CI 1.01 to 1.28).


CONCLUSIONS
The risk of obesity among male shift workers was visually and statistically demonstrated.
Kubo
Tatsuhiko
T
Department of Public Health, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahata-nishi-ku, Kitakyushu, Fukuoka 807-8555, Japan. kubo@med.uoeh-u.ac.jp
Oyama
Ichiro
I
Nakamura
Takehiro
T
Shirane
Kiyoyumi
K
Otsuka
Hirotake
H
Kunimoto
Masamizu
M
Kadowaki
Koji
K
Maruyama
Takashi
T
Otomo
Hajime
H
Fujino
Yoshihisa
Y
Matsumoto
Tetsuro
T
Matsuda
Shinya
S
D000328:Adult; D004812:Epidemiologic Methods; D006801:Humans; D007564:Japan / Q000453:epidemiology; D008019:Life Style; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009765:Obesity / Q000453:epidemiology / Q000209:etiology* / Q000503:physiopathology; D009784:Occupational Diseases / Q000453:epidemiology / Q000209:etiology* / Q000503:physiopathology; D014940:Work Schedule Tolerance; D055815:Young Adult