In a large study, middle-aged women working night shifts
didn't suffer any long-term impairment in their thinking skills.
Previous studies suggested working a mix of day and night
shifts disrupts circadian rhythms, changes in the mind and body that follow a
24-hour cycle. Researchers have thought those disruptions could speed up brain
ageing. "While we had a good rationale for thinking this association might
exist, it simply did not in this dataset," Dr Elizabeth E Devore said.
She led the study at the Channing Division of Network
Medicine of Brigham and Women's Hospital in Boston. The researchers figured
midlife would be a critical window for influencing early changes in the brain
related to later memory loss and cognitive decline, Devore told Reuters Health
in an email.
They looked at data from the Nurses' Health Study, a
long-term study that began in 1976. The current analysis included more than 16 000
female nurses who reported on their history of night-shift work in 1988, when
they were between the ages of 58 and 68. The women reported for how many years
they had worked at least three nights per month in addition to regular day and
Researchers then tested the same women's mental processing
ability and memory by phone in 1995 and 2000, when they were all older than 70.
Exercises included recalling a list of words or repeating a series of numbers
About 1 000 women reported doing at least 20 years of rotating
shift work. Just over 6 000 had never done shift work. Women who reported
rotating night shifts for many years tended to be heavier and have less
education than other women. But they scored similarly on the thinking and
memory tests, the researchers wrote in the American Journal of Epidemiology.
Still many concerns
One limitation of the study, Devore said, is that the
researchers did not have information on which women worked night shifts after
1988. So they could have missed a link between shift work in older age and
Other studies have tied shift work to chronic diseases like
cancer, heart disease, obesity and type 2 diabetes, Devore said. "There is
still plenty to be concerned about regarding shift work," said Jeanne M.
Geiger-Brown of the University Of Maryland School Of Nursing in
Baltimore. "The problem with shift rotation is that the period between two
successive shifts can be shorter than the equivalent number of hours on a day
off between the same shift," she said.
"However, night shifts are difficult, no matter whether
rotating or permanent. "In addition to the potential health risks for
nurses who work night shifts, sleepiness at work could lead to accidents or
harm for the patients they treat, said Geiger-Brown, who studies nursing,
fatigue and cognition. "Whether rotating or permanent, shift work can be
detrimental to health, and the lifetime duration to shift work should be kept
as low as possible," she told Reuters Health.
"Nurses who are concerned about the risk for cognitive
decline can be assured that this risk is not elevated based on this large
epidemiologic study," she said. However, she added, women should do what
they can to reduce their risk of heart disease and diabetes, especially when
they have to work nights.