For patients with advanced breast cancer, a measure of sleep efficiency-the ratio of time actually asleep to time spent in bed-has been found to be predictive of survival time. The study, published in the May issue of Sleep (2014;2014;37:837-842) found that higher sleep efficiency was significantly associated with lower mortality over the ensuing six years, an effect that remained, the researchers noted, after adjusting for baseline prognostic factors such as age, estrogen receptor status, and treatments received.
Mean survival was 68.9 months for "efficient sleepers" compared with 33.2 months for those with poor sleep efficiency. Further analysis found that a 10 percent increase in sleep efficiency reduced the estimated hazard of subsequent mortality by 32 percent. There was no association between sleep duration and survival.
"We were surprised by the magnitude of the relationship between sleep quality and overall survival even after we accounted for medical and psychological variables that typically predict survival," the lead author, Oxana Palesh, PhD, Assistant Professor in the Department of Psychiatry and Behavioral Sciences at Stanford University and Research Director of the Stanford Cancer Survivorship Program, said in a news release. "Good sleep seems to have a strongly protective effect, even with advanced breast cancer."
The study involved 97 women with advanced breast cancer who had a mean age of 55. Objective sleep parameters were measured by wrist-worn actigraphy and sleep diaries for three consecutive days. Overall, participants spent about eight hours in bed at night but slept for only about 6.5 hours.
The authors note that this is the first study to demonstrate the long-term detrimental effects of objectively quantified sleep on survival in women with advanced cancer. The exact mechanism for the relationship remains unclear, but it could be, the researchers said, that sleep disruption may lead to diminished immune function or impaired hormonal stress responses that are more directly responsible for the decrease in survival.
Also commenting in the news release, the President of American Academy of Sleep Medicine, M. Safwan Badr, MD, said, "This study emphasizes the importance of assessing sleep quality among women with breast cancer. Healthy sleep is critical for physical health, quality of life, and overall well-being."
The research was supported by the National Institutes of Health, including grants from the National Cancer Institute and the National Institute on Aging.