Too Little Sleep Cancels Out the Brain Health Benefits of Exercise—Here's Why

Not getting enough sleep can counteract the positive effects that exercise has on the brain, new research finds.

Sleep and exercise each impact cognitive function—brain health. But a new study shows that they also influence each other. So, even if you work out and provide your brain the opportunity to have that cognitive help, a lack of sleep could cancel out that boost.

Jill Barnes, PhD, an associate professor of kinesiology and faculty affiliate at the Wisconsin Alzheimer’s Disease Research Center at the University of Wisconsin-Madison, said the findings remind her of the notion that “you can’t out-run a bad diet.”

“There was an idea that exercise fixes everything, and we know that exercise is important, but other lifestyle habits combined with exercise are key for health,” she told Health.

While a variety of research has linked both sleep and exercise to cognition, researchers in the United Kingdom wanted to better understand how the two pillars of good health intersected when it comes to the brain.

To determine how sleep and exercise work together, the authors of the new study used data from nearly 9,000 adults aged 50 to 95 who were followed for over 10 years as part of the English Longitudinal Study of Ageing, building on what previous research found on the topic.

The group did not include anyone who had been diagnosed with dementia or had signs of cognitive decline at the start.

When comparing sleep and exercise habits, they found that people who were more physically active and got six to eight hours of sleep per night had better cognitive function as they aged than those who exercised but didn’t get at least six hours of sleep per night.

After 10 years, people in that group had the same cognitive function as people who got very little physical activity.

Sleep and exercise both have separate effects on the brain that appear to protect against cognitive decline.

According to Michelle Drerup, PsyD, DBSM, director of behavioral sleep medicine at Cleveland Clinic, sleep plays a major role in clearing toxins from the brain that are associated with Alzheimer’s disease.

The toxins, called beta-amyloid, are produced by several different types of cells in the body, including neurons. Past research has discovered that during sleep, these toxins appear to be eliminated through the lymphatic system.

But, “if you’re not getting enough sleep, these aren’t getting eliminated as well,” said Drerup, who was not involved in the research.

If not eliminated, beta-amyloid builds up in the brain, forming clusters of plaque that disrupt the signals neurons transmit to one another, which contributes to cognitive decline. Beta-amyloid deposits are found in the brains of people with Alzheimer’s disease.

Exercise impacts brain function in a different, yet still critical way.

“There are also studies that suggest that adults with higher levels of physical activity have higher blood flow to certain regions of the brain, and there are several exercise training studies that show improvements in the connections between brain areas,” said Barnes, who was not involved in the new study.

The specifics of how sleep and exercise work together are still unclear, but “this study is suggesting that they do,” Drerup said. It’s possible that not getting the brain benefits that are primarily derived from either sleep or exercise will cancel out the benefits of getting just one of these key activities.

According to Barnes and Drerup, the amount of sleep and exercise each person needs varies, but something everyone can do is build good habits–a little bit at a time.

The Centers for Disease Control and Prevention (CDC) recommends getting about 2.5 hours of moderate activity weekly, or about 75 minutes of vigorous activity every week.

“Adding as little as one bout of vigorous exercise per month could make a difference over 10 years,” said Barnes.

For example, adding a few more minutes of walking every day, or being physically active one more time per week, and increasing goals each month is a great way to gradually increase in a flexible and sustainable way, she said.

The same goes for sleep.

The National Institutes of Health (NIH) recommends adults get between seven and nine hours of sleep each night. This gives “a wide range to determine what works with your natural rhythms and our life,” Barnes said.

If a person isn’t getting at least seven hours of shuteye a night, Barnes recommends using the same gradual approach method.

“When trying to adjust sleeping patterns, start slow and gradually increase, or decrease, sleep,” she said.

By going to bed or waking up 5 or 10 minutes earlier, you can slowly adjust your sleep schedule until you’re regularly getting a healthy amount. Improving exercise may also improve sleep, and vice versa.

“Our bodies work in rhythms and maintaining consistent schedules for sleep and exercise are important for health,” Barnes said. “If both sleep and exercise schedules are out of balance, starting with adding a consistent exercise routine may improve sleep quality, even if sleep duration is short.”

Another key piece of advice: Don’t sweat it too much.

“Stressing about either of these things is counterintuitive,” said Barnes. “Sometimes life gets in the way of optimal schedules for sleep and exercise, or it isn’t possible to have a consistent schedule.”

In those cases, she recommends keeping in mind that the results of this research show that people don’t have to have perfect sleep and exercise schedules every day to get some benefits.

Rather than trying to be flawless, accept that “life gets in the way,” Barnes said. “Then try to get back on track.”