New York, May 3 (IANS) Among the women diagnosed with advanced breast cancer, those who sleep efficiently - not necessarily for longer period - are likely to live longer than those who do not get quality sleep, a study indicated.
Sleep efficiency refers to the ratio of time asleep to time spent in bed.
"Good sleep seems to have a strongly protective effect, even with advanced breast cancer," said Oxana Palesh, an assistant professor at Stanford University.
"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," Palesh noted.
There is no association between sleep duration and survival, the findings of the research showed.
The study involved 97 women with advanced breast cancer who had a mean age of 55 years.
Objective sleep parameters were measured by wrist actigraphy for three consecutive days.
Higher sleep efficiency was significantly associated with lower mortality over the ensuing six years.
Mean survival was 68.9 months for efficient sleepers compared with 33.2 months for participants with poor sleep efficiency.
A 10 percent increase in sleep efficiency reduced the estimated hazard of subsequent mortality by 32 percent, further analysis showed.
Sleep disruption may lead to diminished immune function or impaired hormonal stress responses that are more directly responsible for the decrease in survival, the researchers indicated.
The study appeared in the journal Sleep.