Electrocardiographic, biochemical, and physical data obtained from 237 shif
t and 115 day workers without any obvious disorders were assessed to clarif
y the impact of shift work on cardiovascular functions. The heart-rate corr
ected QT interval (QT(c)) was significantly longer in the shift workers tha
n in the day workers. However, blood pressure, working duration and biochem
ical and other data were comparable between the two work groups. When multi
ple regression analysis was used, shift/day work was significantly related
to the QT(c) in all of the workers. The adjusted odds ratio of shift work,
to the prolonged QT(c) (greater than or equal to 440 ms(1/2)) was 8.15. The
prolonged QT(c) has been thought to contribute to an increased risk of car
diac death. These findings, therefore, suggest that the increased risk for
cardiovascular mortality in shift workers may be attributable to prolongati
on of the QT(c).