Study author Kelly Glazer Baron of the Northwestern University Feinberg School of Medicine in Chicago said exercise is a common prescription for insomnia, but spending 45 minutes on the treadmill one day won't translate into better sleep that night.
"If you have insomnia you won't exercise yourself into sleep right away," Baron said in a statement. "It's a long-term relationship. You have to keep at it and not get discouraged."
This is the first long-term study to show aerobic exercise during the day does not result in improved sleep that same night when people have existing sleep problems, Baron said.
Baron, Kathryn Reid, a research associate professor of neurology at Feinberg, and Dr. Phyllis Zee, a professor of Neurology at Feinberg and director of the Sleep Disorders Center at Northwestern Memorial Hospital, analyzed data from a 2010 clinical trial -- by the same group of Northwestern researchers -- that demonstrated the ability of aerobic exercise to improve sleep, mood and vitality over a 16-week period in middle-age to older adults with insomnia. Baron and colleagues examined the daily sleep data from 11 women ages 57-70.
The study, published in the Journal of Clinical Sleep Medicine, found the women didn't sleep better on nights following exercise, but they did after about four months.
"Women had an increase on average of 45 minutes of their sleep duration," Baron said. "That's as large or larger than most of the behavioral and medication studies."
Patients with insomnia have a heightened level of brain activity and it takes time to re-establish a more normal level that can facilitate sleep, Zee said.
"Rather than medications, which can induce sleep quickly, exercise may be a healthier way to improve sleep because it could address the underlying problem," she said.