What actually happens when you sleep? Here’s how it affects your memory, metabolism and more

Zoë Petersen, Deseret News
Zoë Petersen, Deseret News

Sleep research is a relatively new field of study. Dr. William Charles Dement pioneered sleep research in the 1950s, discovering rapid eye movement cycles, the different phases of human sleep and the “physiological basis of dreams,” according to Stanford Medicine.

Since its 1950s debut, sleep research has found a home at most universities and medical clinics, and studies have found links between healthy sleep and healthy bodies.

But what does sleep actually do to your body? Here’s why — and how — sleep affects your body.

What happens in your body when you sleep?

Dement was a member of the team that discovered REM cycles. He told Global News, “I would go in with a flashlight. There was a person that would be sleeping, and lo and behold, I would see the rapid eye movements. They’re actually very easy to see if you’re sitting next to the sleeper.”

Throughout a typical night of sleep, REM cycles and non-REM cycles compete for brain domination in 90-minute intervals.

During the first half of the night, the 90-minute cycles are mainly taken up by non-REM sleep. In the second half of the night, they’re mostly REM sleep, Dr. Matt Walker, a neuroscience professor at University of California, Berkeley, explained.

“As you go into light stages of non-REM sleep, your heart rate starts to decrease, your body temperature starts to drop and your electrical brainwave activity starts to slow down,” Walker said.

In later stages of non-REM sleep, Walker added, “Deep non-REM sleep will consolidate memories and fixate them into the neural architecture of the brain.”

Daniel Kay, a professor of psychology at Brigham Young University, told the Deseret News that memory consolidation, or “information processing,” is “one of the most significant physiological processes that occurs during sleep.”

Sleep gives the brain the time to reorganize, clear out metabolic waste and wash out misfolded proteins.

In addition to helping renew brain function, blood pressure and heart rate fall during sleep cycles, according to the National Institute of Health.

Specialists at the Mayo Clinic recommend adults get at least seven hours of sleep each night. When the body is sleep deprived, it suffers in the following ways:

How does sleep affect your mental health?

Insomnia and sleep deprivation are heavily associated with mental health issues.

The Centers for Disease Control and Prevention recently found individuals who get less than six hours of sleep at night are “2.5 times more likely to have frequent mental distress” than individuals who slept over six hours.

A study conducted on nearly 9,000 participants, published in the journal Sleep Medicine Reviews, found similar results. The study explained, “Greater improvements in sleep quality led to greater improvements in mental health.”

Kay said, “Insomnia, difficulty going to sleep or going back to sleep when awakened in the night or early morning, in particular, is associated with mental health problems.”

Insomnia prevents certain areas of the brain from sleeping at night. “This, I propose, may explain why they perceive being awake when they appear to be asleep and their predisposition to developing depression and anxiety,” Kay told the Deseret News.

Does your body stop metabolizing after you go to sleep?

Sleep deprivation is correlated with lowered metabolism and an increased risk of cardiometabolic disease, according to research published in the Journal of Lipid Research.

Cardiometabolic diseases are the worldwide leading cause of death, according to the World Health Organization. These diseases include heart failure, Type 2 diabetes and peripheral artery diseases.

How does sleep deprivation decrease metabolism? When the body is sleep deprived, it releases more fatty acids into the bloodstream than normal, which makes it harder for the body to regulate blood sugar levels, per the Journal of Lipid Research.

“Cardiometabolic risk may also be related to the timing of food intake,” the journal added. In a short-term study, researchers found that dinners closer to the participants’ bedtimes were associated with weight gain.

Research from the University of Pennsylvania also shows how sleep deprivation is correlated with high-calorie food consumption. Since adequate sleep regulates hormones that control the body’s appetite (leptin and ghrelin), even short term sleep deprivation can throw off cravings, metabolism and eating tendencies.

However, as quickly as sleep (or the absence of it) can alter the body’s metabolism, the study in the Journal of Lipid Research “hypothesized that these disturbances would partially or fully recover with one night of recovery sleep.”

How does sleep affect the immune system?

According to the CDC, sleep loss negatively influences the immune system in three ways.

First, the body’s ability to fight off infections is reduced since sleep loss reduces natural killer cells (a type of white blood cell that kills diseased cells).

Second, sleep loss is associated with higher levels of inflammatory cytokines and lower levels of protective cytokines. According to the Mayo Clinic, “Certain cytokines need to increase when you have an infection or inflammation, or when you’re under stress.”

When the balance of protective and harmful cytokines is off, the body is at higher risk of metabolic and cardiovascular disorders.

Finally, sleep loss is correlated with lower antibody levels. According to Yale Medicine, “Sleep study results show that when someone has an acute illness, there’s a decrease in rapid eye movement, or REM, sleep,” adding that REM cycles are believed to aid in the body’s ability to recover.

How can sleep affect your memory?

According to Harvard Health, sleep helps the brain “consolidate” memories. Memories made throughout the day move from short-term to long-term memory. This consolidation mainly happens during stage 2: the stage that happens right before the sleeper wakes up.

During sleep, synapses in the brain change to balance out the connections made during the day, according to research published in the journal Frontiers in Neural Circuits. In some cases, “a period of sleep can reduce synaptic strength,” but why and how this happens is still being researched.

However, several studies on both humans and rats referenced in the journal Physiological Reviews suggest that sleeping increases memory. The research explained, “Newer findings characterize sleep as a brain state optimizing memory consolidation.”