Cancer survivors might want to try yoga to get a better night's sleep and to boost their energy levels, according to a U.S. study.

Researchers from the University of Rochester Medical Center in New York randomly assigned more than 400 cancer survivors, most of whom had been treated with chemotherapy for breast cancer, into two groups.

Those who did yoga were able to cut back on sleeping pills and slept better, as measured by a 22 percent increase in sleep quality on a commonly used scale. That was nearly twice the improvement of survivors who didn't do the exercises. Yoga also cut fatigue by close to half, and led to a small increase in quality of life.

That is good news for cancer patients, said researcher Karen Mustian who led the study that will be presented at the American Society of Clinical Oncology Annual Meeting in early June.

How yoga achieves its relaxing effects isn't completely clear.

For cancer survivors seeking help from yoga, Mustian recommended looking for Yoga Alliance-certified instructors, especially those who have experience with people dealing with illness. She also stressed that the results may not apply to all forms of yoga.

"A physician can say with some confidence, "yes, this kind of yoga program may be useful,"" Blayney, who was not involved in the research, told Reuters Health.

"Here we have a studied intervention, one that has been subjected to clinical trials and, lo and behold, it seems to be beneficial.