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 Nurses in the study who worked at least three nights per month were
more likely to develop heart problems over the next 24 years than
nurses who stuck to daytime shifts.
"I think it’s an important message because it’s a potentially
modifiable risk factor," said lead author Celine Vetter, of Harvard
Medical School andBrigham and Women's Hospital in Boston.
For the new study, Vetter and her colleagues used data from more
than 189,000 women. About 40 percent were participating in the
Nurses' Health Study (NHS), which began in 1988. The others were in
NHS2, which began in 1989.
The women entered the studies between the ages of 25 and 55. At the
start, none of them had coronary heart disease, which is when the
arteries that carry blood to heart muscle become narrowed or
blocked.
NHS participants were only asked once about their history of working
night shifts, but NHS2 participants were asked about their night
shifts every two years.
During the follow-up period, there were 7,303 cases of coronary
heart disease problems - like heart attacks, chest pain and bypass
surgeries - in the NHS study and 3,519 cases in the NHS2.
Overall, the risk went up with the number of years women spent
covering night shifts, the researchers report in JAMA.
Compared to the risk for nurses in NHS2 who didn't work night
shifts, the risk of coronary heart disease was 12 percent higher in
nurses who worked night shifts for less than five years, 19 percent
higher in those who worked night shifts for five to nine years, and
27 percent higher in nurses who worked nights for at least 10 years.
But the risk of coronary heart disease came back down as women quit
working night shifts or retired, the researchers found.
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For example, women in NHS with at least 10 years of rotating night
shifts had a 27 percent increased risk of coronary heart disease
during the first half of the follow-up period, but only a 10 percent
increased risk during the second half of the follow-up period.
The study can't explain the association, but Vetter said it could be
related to increased inflammation in the body and social disruption.
She also said the findings may apply to people who work early
morning shifts since they have to get up during the night.
Once researchers have more data, Vetter said, they will be able to
design healthy work schedules.
"Hopefully we can design schedules that are healthier for the
individual," she said.
SOURCE: http://bit.ly/1T2XrW0 JAMA, online April 26, 2016.
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