Exercise and Sleep

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It’s no secret that exercise has extensive benefits for people with diabetes: improving insulin sensitivity, lowering heart disease risk, and helping maintain weight loss, among others. But while any exercise may be good from a health perspective, in reality many people can be very particular about when they exercise. Some people may find that a morning workout gives them an all-day energy boost, while others might spend the day fatigued by the same workout. So a new study that claims evening exercise doesn’t harm sleep may leave many people skeptical.

Published last month by the journal Sleep Medicine, the study analyzed a 2013 survey called the National Sleep Foundation Sleep in America Poll. The survey included 1,000 adults ages 23–60 and asked questions about sleep time and quality; exercise intensity, duration, and timing; and many other sleep-related questions. After adjusting for traits such as age and health status, the researchers found that exercise timing and intensity did have some impact on sleep quality. As noted in a Reuters article on the study, participants who exercised vigorously in the morning were 88% more likely to report sleeping well than those who didn’t exercise, as well as 44% less likely to report waking up feeling unrefreshed. In addition, participants who exercised moderately in the morning were 53% more likely than non-exercisers to report sleeping well.

Participants who exercised in the evening, on the other hand — either moderately or vigorously — didn’t report sleep outcomes that were significantly different from those of non-exercisers. Even though the researchers took this result as an indication that evening exercise doesn’t cause sleep problems, it’s possible that exercising too late in the day cancels out some inherent sleep-enhancing benefit from exercise. It’s also possible, though, that biological or personality differences could explain the association between exercise timing and sleep quality: Maybe the people who choose to exercise in the morning are those who naturally sleep better, while those who exercise later do so because they aren’t as chipper in the morning.

Morning and night aren’t, of course, the only times a person can exercise. Midday workouts have several benefits, as noted in a Wall Street Journal article from last year. The article notes that an afternoon workout can help reverse the fatigue that many people experience at this time of day, potentially leading to increased productivity at work. More moderate exercise seems to be the most helpful in this regard; a high-intensity workout in the middle of a stressful workday can deepen, rather than alleviate, fatigue. And while humans should always take the results of animal studies with a grain of salt, two years ago, a study described in a New York Times blog post found that in mice, the equivalent of an afternoon workout led to cell growth in the area of the brain responsible for sleep regulation.

What’s your experience regarding exercise and sleep — have you found that the timing of your workouts has any impact on your sleep quality? Can someone who’s not already a “morning person” reap the benefits of morning exercise? Could anxiety about early-morning exercise even lead to worse sleep? Does the intensity of afternoon or evening workouts have any effect on how you sleep? Leave a comment below!

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