Question

Late-day exercise: Can it cause insomnia?

I prefer to exercise in the early evening, but I have been told this may worsen insomnia. Is this true?

Answer

from Timothy Morgenthaler, M.D.

Several studies indicate that regular exercise improves sleep in people with insomnia. But how the timing of exercise affects your own ability to fall asleep is unclear.

Most people with chronic insomnia have increased levels of stress hormones in their blood, suggesting that they are abnormally sensitive to stress (hyperaroused). The higher your stress hormone levels, the worse your sleep is. Exercise initially increases such stress hormones. But several hours after a workout, the stress hormones decrease.

The time it takes for stress hormones to decrease following exercise varies. Because each person is different, you may consider trying this experiment if you're having trouble falling asleep:

• For two weeks, exercise close to bedtime. Each morning, rate your quality of sleep on a scale of 1 to 10.
• For the next two weeks, exercise in the morning or in the early afternoon. Each morning, rate your sleep quality.
• For each week, add up your ratings and divide by the total number of days you've rated. This will give you an average score for each week.

This can show you how the timing of your exercise may affect your sleep and help you determine the time of day that's better for you to exercise.