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 Compared to women sleeping eight hours a night, women who slept at
least nine hours were 46 percent more likely to die of breast
cancer, the study found. After up to 30 years of follow-up, the
women who got more sleep were also 34 percent more likely to die of
other causes.
“Sleep duration, but also changes in sleep duration before versus
after diagnosis, as well as regular difficulties to fall or to stay
asleep, may also be associated with mortality among women with
breast cancer,” said lead study author Claudia Trudel-Fitzgerald of
the Harvard T.H. Chan School of Public Health in Boston.
“Given that long sleep duration has been associated with mortality
among cancer-free individuals, as well as among breast cancer
patients in recent studies including ours, it is possible that the
relationship of sleep duration with survival also exists for other
types of cancer,” Trudel-Fitzgerald said by email. “However, further
research is warranted.”
For the study, researchers examined data on post-diagnosis sleep
duration for 3,682 women with breast cancer. They also examined
pre-diagnosis sleep duration in a subset of 1,949 women and
post-diagnosis sleep difficulties in a subset of 1,353 women.
At diagnosis, women were 65 years old on average and most had what’s
known as stage one or two tumors, meaning malignancies hadn’t spread
beyond the breast or nearby lymph nodes.
At least half the women in the study were still alive 11 years after
their diagnosis.
During the study, there were 976 deaths, including 412 caused by
breast cancer, researchers report in the British Journal of Cancer.
Among the subset of women who had data on pre-diagnosis sleep
duration, sleeping longer after their diagnosis was associated with
35 percent higher odds of death from all causes and 29 percent
greater likelihood of death from breast cancer.
For the group of patients who had data on sleep difficulties,
researchers found women who regularly struggled to fall or stay
asleep were 49 percent more likely to die from all causes than women
who rarely or never had these issues.
The study wasn’t a controlled experiment designed to prove that time
spent sleeping directly influences survival after a breast cancer
diagnosis.
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Other limitations of the study include its reliance on women to
accurately recall and report on their own sleep duration and
quality, the authors note. It’s also possible that breast cancer
contributes to sleep problems rather than sleep difficulties
increasing the odds of mortality after a cancer diagnosis,
researchers point out.
“People who are sicker are more likely to be fatigued from their
illness, be it breast cancer or other cause, and thus sleep more,”
said Cheryl Thompson, a researcher at Case Western Reserve
University in Cleveland, Ohio, who wasn’t involved in the study.
In the current study, patients who reported getting more than nine
hours of sleep were also more likely to be obese and have more
advanced cancer, Thompson said by email.
Some patients might sleep more because they get less physical
activity, spend more time in bed, or experience more social
isolation or depression, said Kristen Knutson, a researcher at the
Center for Circadian and Sleep Medicine at Northwestern University’s
Feinberg School of Medicine in Chicago.
When patients do notice changes in how long or how well they sleep,
it is worth discussing with their doctor, Knutson, who wasn’t
involved in the study, said by email.
“Sleep should be considered a vital sign,” Knutson said. “Changes in
sleep and excessive sleepiness are important signs that physicians
can use to help care for their patients.”
SOURCE: http://go.nature.com/2pasqsh British Journal of Cancer,
online March 30, 2017.
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