Extra sleep or Exercise.

That alarm hits at 6 a.m. and you have a choice: smash the snooze button or get up and get your workout in. What should you do? 

Science hasn't given us a solid answer on this yet. 

As there are only 24 hours in a day, it’s no wonder that we often feel pressed to choose between just a little more sleep or exercise when it comes to the few precious hours we have to ourselves. But for your health and happiness, you need to be getting enough sleep and fitting in exercise several times a week -- you know, between work, family, friends and all the rest of your myriad responsibilities. 

Considering how common this conundrum is, it’s surprising how few studies there are on the issue. Christopher Kline, an exercise and sleep researcher at University of Pittsburgh’s Physical Activity and Weight Management Research Center, has long wanted to conduct a long-term experiment that could tell us what the health effects would be of displacing a bit of sleep for exercise -- or skipping exercise for more sleep. But given the lack of research, Kline says there’s no clear answer on the issue. 

The only studies available to work with are correlational studies that can only suggest relationships -- not cause and effect -- between certain behaviors (such as sleep, light exercise, moderate and vigorous exercise and sedentary time) and certain health outcomes.

The case for more sleep (or at least more snooze button)

"A couple of studies that have looked at the day-to-day relationships between exercise and sleep in adults have found that better sleep is associated with greater exercise behavior the next day, but in these same studies exercise is rarely associated with better sleep the subsequent night,” Kline explained.

In other words, it makes sense that being more energized ups your chances of getting in a good workout the next day, but studies suggest that this doesn't necessarily lead to a virtuous cycle of satisfying sleep and regular exercise.  

The case for just putting on those sneakers and pushing through

The most convincing research to date on this topic uses what’s known as “isotemporal substitution modeling,” according to Kline, in which researchers statistically analyze data on large cohorts of people to see what the effects of substituting one activity for another would be on their health. 

This 2013 study of over 2,000 people, for instance, finds that switching 30 minutes of sleep with either moderate or vigorous physical activity was linked to health outcomes associated with better cardiovascular health: A smaller waist, higher levels of HDL cholesterol (the “good” cholesterol), lower levels of triglycerides, or fat in the blood, and lower blood sugar and insulin levels.

Interestingly, it also found that switching sleep for 30 minutes of sedentary behavior (say, watching TV or using a computer) was also linked to lower insulin levels and better regulation of insulin release. So in that case, the data suggests that if you're choosing between just one more “Masters of None” episode on Netflix or sleep, you should choose sleep. 

A similar study of over 200,000 middle aged people, published in 2015, found that if you slept less than seven hours, replacing one hour of walking or exercise with one hour of sleep was linked to a seven percent greater mortality risk. And if you slept more than seven hours, swapping exercise for sleep was linked to an 18 percent greater risk.

It's a tie, but exercise has an edge

Given these two studies, Kline said there was no clear answer. But if he had to choose, he would tentatively select 30 minutes of exercise over 30 more minutes of sleep, assuming that he's getting a decent amount of rest (six to eight hours per night), and that the amount of sleep he gets is enough to keep him going throughout the day. 

And remember: While it might seem that Kline is prioritizing exercise over sleep, note that he'd only choose exercise if the amount of sleep he'd get was a healthy one for him. To make sure your sleep is the best it could be, check out these tips on how to have the best sleep ever. 

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