By Robert Preidt
The study, which was not designed to prove cause-and-effect, included more than 18,000 cancer patients whose progress was tracked in the Women's Health Initiative study.
All of the women provided information about a number of aspects of their sleep prior to their cancer diagnosis, including the amount of sleep they got, whether or not they snored, and any history of insomnia.
Researchers led by Amanda Phipps, an assistant professor of epidemiology at the University of Washington in Seattle, found that women who slept 6 hours or less per night and were frequent snorers had more than twice the odds of a poor prognosis compared to women with neither of those factors.
The study was published online in the journal Sleep and was also presented June 10 at the annual meeting of the Associated Professional Sleep Societies in Seattle.
"Our results suggest that sleep duration is important for breast cancer survival, particularly in women who snore," Phipps said in a journal news release.
Two breast cancer experts were cautious in interpreting the study results, however.
"At first glance it seems as though recommending more sleep could be of benefit [to breast cancer patients]," said Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City. "However, one must remember that perhaps the factors that allow women to have more restful sleep -- such as healthier lifestyle or lower amounts of stress -- are the real reasons women who sleep well have better breast cancer outcomes."
Dr. Charles Shapiro co-directs the Dubin Breast Center at the Mount Sinai Hospital, also in New York City. "Sleep patterns often get disrupted, and insomnia is prevalent, in women who are diagnosed and treated for breast cancer and other cancers," he said.
"Precisely why insomnia is prevalent in cancer populations is unknown, but there are many potential causes including depression, anxiety, fatigue and [other issues] such as hot flashes," Shapiro added.
But he agreed with Bernik that "important factors like depression and obesity, known to be associated with increased breast cancer mortality, were not assessed [in the study]," and they could be the link between sleeplessness and breast cancer outcomes.
"Insomnia is a common but under-recognized and undertreated problem among breast cancer survivors," Shapiro said, "but whether it actually causes increased cancer deaths is unknown and we need a lot more information before we make that link."