Karen Mustian of the University of Rochester Medical Center in New York said some cancer patients might have trouble sleeping because of a worsening sleep problem they had even before their cancer diagnosis.
Mustian analyzed data involving survivors with sleep problems who did yoga for 75 minutes twice a week for a month.
The study, published in the Journal of Clinical Oncology, found cancer survivors who took up a form of gentle yoga slept better.
"While they showed greater improvements in their overall rating of their sleep, they really showed improvements in feeling less tired during the day and napping less," Mustian said in a statement.
Penelope Cruz named 2013's 'Best Body' by Fitness magazine
Susan Sarandon: I was stoned at almost every awards show