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Sleep efficiency - ratio of time asleep to time spent in bed - is predictive of survival time for women with advanced breast cancer, according to a new study. 

The study found that a 10 percent increase in sleep efficiency reduced the estimated hazard of subsequent mortality by 32 percent. However there wasn't any association between sleep duration and survival, according to the study. 

"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," said 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, in the press release.  "Good sleep seems to have a strongly protective effect, even with advanced breast cancer."

The study was carried upon on nearly 100 women with advanced breast cancer who had a mean age of 55 years. Overall, subjects of the study spent about eight hours in bed at night and slept for 6.5 hours.

"This study emphasizes the importance of assessing sleep quality among women with breast cancer," said American Academy of Sleep Medicine President Dr. M. Safwan Badr, in the press release. "Healthy sleep is critical for physical health, quality of life and overall well-being."

Authors of the study said it was the first study that demonstrated the long-term detrimental effects of objectively quantified sleep on survival in women with advanced cancer. 

"There are effective treatments for sleep disruption in the general population, and some of them have shown to be effective in cancer survivors as well," said Palesh.  "But much more research is needed to develop and test interventions that are adapted for cancer patients and survivors.  These interventions might not only improve quality of life, but can potentially improve survival."

Findings of the study are published in the May 1 issue of journal Sleep.