work a mix of day and night shifts may face a greater risk
of dying from heart disease than those who work fixed days
or nights only, a new study from Japan suggests. Also, the
effect of heart disease risk factors such as high blood
pressure, obesity, excessive alcohol consumption and
cigarette smoking was even greater for individuals who
worked rotating shifts, Dr. Yoshihisa Fujino and his
colleagues report in the American Journal of Epidemiology.
Fujino of the University of Occupational and Environmental
Health in Kitakyushu and his team looked at 17,649 men
aged 40 to 69 participating in a study of cancer risk.
Nearly 84 percent chiefly worked days, while about 5
percent worked nights only, and roughly 11 percent were on
Over a period of about 13 years,
1363 of the men died, with 86 of these deaths due to heart
Men who worked rotating shifts were 60 percent more likely
than those who worked day shifts to have diseases of the
heart and blood vessels, and they were 2.32 times more
likely to die of heart disease such as a heart attack. And
if men had other risk factors for heart disease, the
effect of rotating shift work was even stronger. For
example, rotating shift workers with high blood pressure
were 3.4 times more likely to die of heart disease than
day workers with high blood pressure.
However, men who worked fixed nights were at no greater
risk for heart disease or death from related causes than
those who worked days only.
Past studies have suggested that difference in health
among people working different shifts may be due to
differences in heart disease risk factors -- for example,
people who work nights may be more likely to smoke than
those who work days. However, in the current study, the
effect of rotating shift work persisted even after the
researchers used statistical techniques to adjust for such
Shift work is known to affect circadian rhythms and body
functions such as blood pressure,
heart rate and hormone secretion, Fujino and his
colleagues note. It may be more difficult people's
circadian rhythms to adapt to a rotating shift than to
steady nighttime work, they suggest.