Researchers found study participants, mostly women with a history of breast cancer, reported significant improvements in sleep quality and sleep duration when they attended yoga sessions twice per week.
The study's lead author called it "the kind of study that doctors typically look to when changing the standard of care with patients."
"One of the biggest messages from the trial is yoga worked," Karen Mustian, from the James P. Wilmot Cancer Center at the University of Rochester Medical Center in New York, said.
"Regardless of whether people had mild sleep disruption or a clinical diagnosis of insomnia, people who participated in yoga experienced the same amount of sleep improvement," she told Reuters Health.
Mustian said between 30 and 90 percent of cancer survivors report some form of sleep disturbance.
That can be due to anxiety about a cancer diagnosis, related health problems or side effects of treatments including surgery, chemotherapy, radiation and hormone therapy.
Studies suggest yoga can lower blood pressure and improve anxiety, depression and insomnia. The program used in this study included Gentle Hatha yoga, which focuses on physical postures, and Restorative yoga, with an emphasis on relaxation, breathing and meditation.
The study included 410 people with a history of cancer who were recruited from 12 US cities. Participants were 54 years old, on average. Almost all were white and female, and three quarters had had breast cancer.
Participants were randomly assigned to one of two groups. Half of them attended a standardised yoga programme for cancer survivors that met for 75 minutes twice a week, in addition to receiving standard care. The other half received only standard care.
The researchers assessed participants' sleep quality before and after the four-week study period on a questionnaire and using actigraphy, a sensor that detects movement and is worn like a wristwatch at night.
People in both groups improved on measures of overall sleep quality and several other sleep-related variables. Relative to the control group, however, those who did yoga saw greater improvements in sleep quality, daytime sleepiness and the amount of time actually spent sleeping while in bed.
On a scale of general sleep quality - measured from 0 to 21, where lower scores indicate fewer problems - yoga participants improved from a 9.2 to a 7.2 during the study. Those in the comparison group improved from a 9.0 to a 7.9, on average, according to results published in the Journal of Clinical Oncology.
What's more, yoga participants reduced their use of sleep medication by 21 percent per week, on average, and those not assigned to yoga increased use of sleep aids by five percent per week.
"What's exciting about this study is that it brought yoga out to people where they're receiving care and still showed that there's benefits to yoga participation," Dr Donald Abrams, an oncologist at the University of California, San Francisco Osher Center for Integrative Medicine, told Reuters Health.
Abrams, who was not involved in the new study, said it's not clear why people in the comparison group improved on sleep measures, albeit to a smaller extent than those who did yoga. He also wondered whether the results would apply to other groups of patients.
"The data from other studies is quite clear that yoga improves quality of life for breast cancer patients, and this study confirms that," he said. "We still don't know how it works in men with colon or prostate cancer, for example, because those patients are never really involved in these trials."
Still, he said he often recommends yoga to his patients with cancer.
"People can do it at home, or they can take a class," Abrams said. "The cost is not enormous, and it's definitely better than taking sleeping pills."