After a night of tossing and turning or seriously truncated snooze time, you’ve probably felt physically ragged and mentally dulled. Not at your best, in other words. You may have had trouble thinking clearly or focusing intently on what you were doing. Your reaction time may have been slower than usual. You may have felt somewhat lethargic. And your mood may have been less than upbeat. Looking around, you might have felt at a distinct disadvantage compared to the well-rested people around you who are operating on a higher level.
On the flip side, sufficient sleep can help you feel good and think more clearly.
There’s no denying that getting sufficient sleep is essential for your physical and mental well-being.
Contrary to popular perception, sleep isn’t a passive state. While you’re asleep, the cells and tissues in your body and brain work to repair tissues, remove toxins from the brain, and consolidate new knowledge and memories, among other things. Sleep also affects hormones, immune system functioning, metabolism, bone maintenance, and respiratory and cardiovascular health, among other biological functions.
“During sleep, we heal our bodies through a number of different pathways,” says Jade Wu, Ph.D., a sleep researcher at the Duke University School of Medicine and author of Hello Sleep. “Sleep affects our cardiovascular function, including our ability to absorb oxygen. It affects the release of human growth hormone, which promotes various forms of recovery, and the immune system is boosted so inflammation is reduced.”
There’s considerably more research about how too little sleep negatively affects people’s performance than about how the optimal amount improves it. But, experts say, patterns can be extrapolated from scientific studies on both sides of the sleep spectrum. Let’s take a closer look.
Sleep and Physical Performance
Getting enough good-quality sleep is beneficial for energy, stamina, strength, and other physical effects. The exact mechanisms behind these sleep-related influences aren’t fully understood. “It’s a combination of optimizing neurotransmitter amounts and ratios, improving hormone levels, particularly growth hormone, and changing energy management via ATP [adenosine triphosphate] at the level of the mitochondria,” which act as the cells’ power plants, says Dr. Chris Winter, a neurologist, sleep specialist, and sleep advisor to numerous professional sports teams across the NFL, MLB, NBA, and NHL.
Winter’s work with athletes is critical for helping them achieve success on the field. After all, getting sufficient sleep is important for physical recovery from exercise. In a study published in a 2021 issue of the journal Frontiers in Sports and Active Living, researchers found that university athletes who regularly sleep eight or more hours per night were less likely to experience injury or illness over a one-year period. This makes sense given that your body releases growth hormone, which repairs exercise-induced damage to muscles, while you’re in the deeper phases of sleep. For athletes who are exercising more frequently, the recovery time sleep gives them becomes even more important. “There are two sides to performing. There’s performing and then there’s the preparation and getting ready for the next game,” Winter says. “Sleep is doing double duty. So it’s essential to perform your best today but also essential for getting you ready to shake off the effects of your last game and get ready for the next one in a way that you’re not risking injury or chronic pain.”
By contrast, skimping on sleep can have detrimental effects on various aspects of physical performance. A review of the research, published in a 2022 issue of the journal Sports Medicine, found that when people get six or fewer hours of sleep per night, it has a negative effect on their exercise performance — including their speed, power, strength, endurance, and skills — the next day, especially in the afternoon.
In addition, “studies have shown that insufficient sleep affects aerobic capacity, running speed, and stamina,” says Winter. The effects aren’t limited to your speed and strength. “Physical performance also relies on mental acuity, concentration, reaction time, risk management, coordination, and memory — all of these cognitive attributes are dependent on sleep.”
Poor sleep can also make the physical activity you do feel harder, causing you to become exhausted sooner than you would after a good night’s sleep, research has found.
Not surprisingly, people who exercise intensely may need more sleep than their less active peers do, and this is true at any age. “Athletes need more sleep to function optimally, to repair tissue in the body, and make up for energy expenditure from sports,” Wu explains.
If you scale back your sleep, you limit your potential to achieve maximum physical performance, especially on a long-term basis.
Sleep and Cognitive Performance
After a good night’s sleep, you’re more likely to feel like you’re firing on all cylinders, mentally. Your processing speed and memory are likely to be better. You’re probably able to be more productive, think clearly, and pay attention to details. “When people sleep well, they’re better able to tune out noise and pay attention to what they want to focus on,” Wu says. “They’re able to keep track of one thing and follow a train of thought.”
These effects may occur partly because “on a basic level, deep sleep filters junk out of the brain, making it able to form new pathways,” Wu explains.
In fact, sleep is so beneficial to cognitive performance that research has even found that a nap in the early afternoon can improve alertness, attention, memory function, and reaction time, among other aspects of cognitive function.
On the flip side, poor-quality sleep or too little sleep can take a toll on cognitive function. A study in a 2021 issue of the journal Sleep found that postmenopausal women with fragmented sleep have slower information-processing capabilities. Another study found that restricted sleep can have a negative effect on cognitive flexibility (the ability to shift attention easily or adapt to changing tasks), which is essential for pilots, air traffic controllers, surgeons, and emergency responders, among others, not to mention simple but disparate domestic responsibilities at home.
And research has found that poor sleep can compromise cognitive motivation, which can have unfortunate ripple effects on your work performance and even your adherence to an exercise regimen.
In addition, the quality and quantity of your sleep can affect your ability to regulate your emotions. When people are sleep deprived, they may have trouble with self-control and inhibition, as well as experiencing reductions in trust and empathy, according to research. In fact, a study in a 2023 issue of the journal Nature and Science of Sleep found that when people were subjected to a night of lost sleep, their ability to cognitively reappraise emotion-eliciting situations was compromised; as the researchers noted, this could undermine the effectiveness of cognitive therapy to improve someone’s ability to regulate their emotions.
Besides leaving you feeling emotionally frayed, these effects could compromise your work performance — by making it hard for you to stay calm and field questions while giving a presentation without getting flustered, Wu says.
Ultimately, the amount of sleep people need to feel and function at their best is somewhat individual (though the average is seven to nine hours per night for adults). “The amount of sleep you need depends on how much cellular metabolic activity you’ve used up during the day through physical, mental, and social activity,” Wu says. Regularly replenishing those spent resources is essential to optimizing your performance, whether on the field, at your desk, on the road, or in a normal night at home.
