A new US study finds that it takes as long as four months for patients with insomnia to benefit from regular daily exercise.

It also finds that poor sleep can cause people to reduce the amount of exercise they do, and the researchers urge people with insomnia to persist and not expect exercise to be a quick cure.

A report on the study is online in the August 15th issue of the Journal of Clinical Sleep Medicine.

Lead author and clinical psychologist Kelly Glazer Baron PhD, said: "If you have insomnia you won't exercise yourself into sleep right away." Dr Baron, who is director of the behavioral sleep program at Chicago's Northwestern University Feinberg School of Medicine, added:

"It's a long-term relationship. You have to keep at it and not get discouraged."

Several studies have already shown that people find their sleep quality improves significantly with exercise, and there is also evidence that it improves objective measures of sleep.

But most previous studies on the effect of daily exercise on sleep have focused on healthy sleepers.

Baron and colleagues are the first to report a long-term study that shows aerobic exercise during the day does not help those with insomnia sleep better straight away.

In other words, if you have problems sleeping, then hitting the treadmill for 45 minutes during the day does not mean you will sleep any better that same night.

Poor sleep does not affect your aerobic capacity, says Baron, but it changes your perception of exertion, so you feel more exhausted.

Listening to people with insomnia

Baron decided to do the study, which analyzed the daily effects of exercise on sleep, after hearing people with insomnia complain that exercise recommendations were not having an effect straight away.

A common complaint was "I exercised so hard yesterday and didn't sleep at all," says Baron, explaining that there was a belief in exercise improving sleep - because of all of the studies that had been done. But she wondered if perhaps, with insomnia, it is not that straightforward.

In 2010 Baron and the team had run a 16-week clinical trial that found daily aerobic exercise did not boost sleep, mood and vitality in 11 sedentary middle-aged to older women diagnosed with insomnia. Older women are the group most affected by insomnia.

Exercise is considered an ideal way to improve sleep in older people because medication can affect memory and increase the risk of falls.

For this latest study, the researchers looked at trial data differently. They looked at the long-term pattern rather than the daily one and found exercise did affect sleep (but not straight away), and just as importantly, sleep affected exercise.

So it seems there is a chance of getting caught in a vicious cycle: poor sleep leads to less exercise, which means you are less likely to reap the long-term benefits.

Baron says the key message for people with sleep problems to escape the vicious cycle is to persist.

"People have to realize that even if they don't want to exercise, that's the time they need to dig in their heels and get themselves out there," Dr Baron says, urging:

"Write a note on your mirror that says 'Just Do It!' It will help in the long run."

Senior author Phyllis Zee, director of the sleep disorders center at Northwestern Memorial Hospital, says the benefits will not happen overnight because:

"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."

"Rather than medications, which can induce sleep quickly, exercise may be a healthier way to improve sleep because it could address the underlying problem," says Zee, who concludes: "... in the end, sleep still trumps everything as far as health is concerned."

Baron sees no reason why the results should not work for men too, as there is no evidence of gender differences in lifestyle treatments for insomnia.

Funds from the National Institute of Health, the National Institute on Aging, the National Heart, Lung and Blood Institute, and the National Center for Advancing Translational Science helped finance the study.

Advocates of how to get a good night's sleep suggest you start winding down for the night before you feel exhausted, and also keep your bedroom clear of distractions and gadgets that keep your brain overactive.

A recent study also found that bedtime use of smartphones and tablets can disrupt sleep because of the effect the light they emit has on melatonin, a hormone that helps control the natural sleep-wake cycle.

Written by Catharine Paddock PhD