Sleep ranks right up there with eating healthy and exercising as one of the most important things you can do day after day (and night after night) to keep your body and mind working at their best.
A night of poor sleep can have lots of consequences on mood and functioning the following day. It’s harder to focus; you may be more irritable; pain can actually feel more intense. And chronically, not sleeping well can result in increased risk of a lot of health problems in the long-term.
Pretty much every cell in the body relies on sleep in some regard to function the way it should, explained Dr. Michael Awad, chief of sleep surgery at Northwestern Medicine. “Sleep is a pillar of our health.”
The body has its own internal clock, which regulates the various circadian rhythms of the body, Awad explained. Every system in the body — like metabolism, immune function and cardiovascular function — has its own internal schedule for functioning optimally, which get regulated by the master internal clock. Hormones get released at certain intervals to trigger things like digestion, raising body temperature and feeling tired.
Going to sleep and waking up at the same time day after day is what keeps this master clock (and all those other timetables for the various systems of the body) running as they should.
Sleep researchers have also identified a lot of important processes that happen in the brain and body during sleep that promote physical and mental health long term.
The National Sleep Foundation recommends getting 7 to 9 hours of sleep per night. And in addition to getting enough hours of sleep, it’s important to get good quality sleep, too, Awad said. That means you should be going to sleep and waking up at approximately the same time each night and morning, and sleeping soundly for the hours you’re in bed.
Here’s what we know about why those hours of quality sleep are so worth your while.
Sleep recharges the body and mind for the day ahead
In the short-term, sleep prepares your body and mind for the day ahead. “Sleep seems to be the way the body re-charges,” explained Dr. Alcibiades J. Rodriguez, a sleep medicine physician and director of the Epilepsy SLEEP Lab at NYU Langone Health in New York City.
If you don’t sleep well, the next day you may notice sleepiness, fatigue, lack of energy, irritability, decreased concentration and even decreased reaction time, he said. (Studies in collegiate basketball players show, for example, athletic performance — measured via shooting averages and sprint times — improved with more sleep.)
Sleep also plays an important role in remembering things. Studies show that key processes in learning that help new things you learn “stick” in long-term memory don’t actually happen (or don’t happen how they’re supposed to) when you don’t get enough sleep. Think of it as the scientific explanation as to why pulling an all-nighter to learn something for an exam doesn’t actually work.
Unlike taking out a loan from the bank, our body can only pay back so much of our sleep debt from being chronically deprived on sleep.
Sleep supports mental health
The relationship between sleep and mental health is complex, Awad said. There’s evidence that not getting enough sleep can increase likelihood of problems like anxiety and depression, but in people with those problems, the symptoms of those conditions tend to make it harder to sleep. Sometimes it can be difficult to determine which comes first: the mood problem or the sleep problem.
What is clear is that getting enough and good quality sleep supports good mental health and well-being. Research shows that many of the key chemicals in the brain that help regulate mood and emotions get altered after a bad night of sleep, Awad said. Rapid Eye Movement (REM) sleep — the stage of "deep sleep" when dreaming is thought to be most likely — appears to play a really important role in this emotional regulation aspect of sleep, Awad said.
What’s important for people to know is that if you are having trouble sleeping as a result of (or in addition) to having depression, anxiety or another mental health problem, you may need separate treatment to help your sleep. And in some cases treating the sleep problem can help improve the other symptoms, too, Awad said.
Consistently sleeping well promotes long-term health and wellbeing
Night after night, sleep supports functioning of all systems of the body. If you’re consistently not sleeping well, however, the damage to various systems of the body can start to show up.
There’s evidence, for example, that sleep helps regulate the release of the hormones responsible for appetite and feeling “full” from the food you eat — and that sleep deprivation over time can lead to weight gain. There’s also evidence that during sleep the brain clears toxins that have specifically been linked to cognitive decline and different types of dementia, Awad explained. And while research is still in the early phase, some studies suggest people who consistently sleep less may be at increased risk of Alzheimer’s disease.
Research has also linked poor sleep to increased risk of Type 2 diabetes, obesity and cardiovascular disease.
The bottom line: Don’t beat yourself up for a bad night of sleep — it happens from time to time, said Awad. But do focus on making good choices and developing healthy habits that promote sleeping well over the long-term. “Unlike taking out a loan from the bank, our body can only pay back so much of our sleep debt from being chronically deprived on sleep,” he said.