Sleep gives your body time to repair itself and carry out important functions, like clearing out waste and releasing hormones. Without these processes, our bodies can’t function correctly.
Getting enough sleep is essential for maintaining good health. We need sleep to survive — just like we need food and water. So, it’s no surprise that we spend about
Let’s take a closer look at why we sleep, along with what happens when we don’t get enough.
Several biological processes happen during sleep:
- The brain stores new information and gets rid of toxic waste.
- Nerve cells communicate and reorganize, which supports healthy brain function.
- The body repairs cells, restores energy, and releases molecules like hormones and proteins.
A lot is still unknown about the purpose of sleep. To date, scientists have found that sleep helps the body in several ways. The most
According to the energy conservation theory, we need sleep to conserve energy. Sleeping allows us to reduce our caloric needs by spending part of our time functioning at a lower metabolism.
This concept is backed by the way our metabolic rate drops during sleep. Research suggests that 8 hours of sleep for human beings can produce a daily energy savings of 35% per 24-hour cycle.
Another theory, called the restorative theory, states that the body needs sleep to restore itself.
The idea is that sleep allows cells to repair and regrow. This is supported by many important processes that happen during sleep, including:
- muscle repair
- protein synthesis
- tissue growth
- hormone release
The brain plasticity theory says that sleep is required for brain function. Specifically, it allows your neurons, or nerve cells, to reorganize.
When you sleep, your brain’s glymphatic (waste clearance) system clears out waste from the central nervous system. It removes toxic byproducts from your brain, which build up throughout the day. This allows your brain to work well when you wake up.
Research suggests that sleep strengthens memories. It also allows the brain to erase or forget unneeded information that might otherwise clutter the nervous system.
Sleep affects many aspects of brain functioning, including:
- learning
- memory
- problem-solving skills
- creativity
- decision making
- focus
- concentration
Similarly, sleep is necessary for emotional health. During sleep, brain activity increases in areas that regulate emotion, supporting healthy brain function and emotional stability.
Areas of the brain in which sleep increases activity include the:
- amygdala
- striatum
- hippocampus
- insula
- medial prefrontal cortex
One example of how sleep can help regulate emotions occurs in the amygdala. This part of the brain, located in the temporal lobe, is in charge of the fear response. It controls your reaction when you face a perceived threat, like a stressful situation.
When you get enough sleep, the amygdala can respond in a more adaptive way. But if you’re sleep deprived, the amygdala is more likely to overreact.
Research from 2017 suggests that sleep and mental health are intertwined. On the one hand, sleep disturbances can contribute to the onset and progression of mental health issues, but on the other hand, mental health issues can also contribute to sleep disturbances.
Sleep affects your weight by controlling hunger hormones. These hormones include ghrelin, which increases appetite, and leptin, which increases the feeling of being full after eating.
Ghrelin decreases during sleep because you’re using less energy than when you’re awake.
But lack of sleep elevates ghrelin and suppresses leptin. This imbalance makes you hungrier, which may increase the risk of eating more calories and gaining weight.
Research from 2022 found that chronic sleep deprivation may be associated with an increased risk of:
Insulin is a hormone that helps your cells use glucose (sugar) for energy. But when you have insulin resistance, your cells don’t respond properly to insulin. This can lead to high blood glucose levels and, eventually, type 2 diabetes.
Sleep may protect against insulin resistance. It keeps your cells healthy so they can easily take up glucose.
The brain also uses less glucose during sleep, which helps the body regulate overall blood glucose.
A healthy and strong immune system depends on sleep. Research from 2019 suggests that sleep deprivation can inhibit the immune response and make the body susceptible to germs.
When you sleep, your body makes cytokines, which are proteins that fight infection and inflammation. It also produces certain antibodies and immune cells. Together, these molecules prevent sickness by destroying harmful germs.
That’s why sleep is so important when you’re sick or stressed. During these times, the body needs even more immune cells and proteins.
While the exact causes aren’t clear, scientists think sleep supports heart health. That’s because there’s a link between heart disease and poor sleep.
The
Lack of sleep is associated with risk factors for heart disease, including:
- high blood pressure
- increased sympathetic nervous system activity
- increased inflammation
- elevated cortisol levels
- weight gain
- insulin resistance
Your body cycles through four stages of sleep. This cycle occurs multiple times throughout the night for different lengths of time, varying from
The pattern includes two major phases of sleep: non-rapid eye movement (non-REM) sleep and rapid eye movement sleep (REM) sleep. The four stages of sleep include three stages of non-REM sleep and one stage of REM sleep.
As the names suggest, non-REM sleep features an absence of eye movements. REM sleep, when dreaming occurs, is characterized by rapid eye movements.
Stage 1: Non-REM sleep
Stage 1 occurs when you first fall asleep. As your body enters light sleep, your brain waves, heart rate, and eye movements slow down.
This phase lasts for about 7 minutes.
Stage 2: Non-REM sleep
This stage involves light sleep just before deep sleep.
Your body temperature decreases, your eye movements stop, and your heart rate and muscles continue to relax. Your brain waves briefly spike and then slow down.
During a night of sleep, you spend the most time in stage 2.
Stage 3: Non-REM sleep
In stages 3 and 4, deep sleep begins. Your eyes and muscles don’t move, and your brain waves slow down even further.
Deep sleep is restorative. Your body replenishes its energy and repairs cells, tissues, and muscles. You need this phase to feel awake and refreshed the next day.
Stage 4: REM sleep
REM sleep first happens about 90 minutes after you fall asleep. During this stage, your eyes move quickly from side to side.
Your brain waves and eye movements increase. Your heart rate and breathing also speed up.
Dreaming often occurs during REM sleep. Your brain processes information during this stage, making it important for learning and memory.
The recommended amount of sleep depends on your age. It also varies from person to person, but the
- birth to 3 months: 14 to 17 hours
- 4 to 12 months: 12 to 16 hours per 24 hours, including naps
- 1 to 2 years: 11 to 14 hours per 24 hours, including naps
- 3 to 5 years: 10 to 13 hours per 24 hours, including naps
- 6 to 12 years: 9 to 12 hours
- 13 to 18 years: 8 to 10 hours
- 18 to 60 years: 7 or more hours
- 61 to 64 years: 7 to 9 hours
- 65 years and older: 7 to 8 hours
Without enough sleep, your body has a hard time functioning properly. Sleep deficiency is
Lack of sleep is also associated with an increased risk of injury for both adults and children. Driver drowsiness, for example, can contribute to serious car accidents and even death.
In older adults, poor sleep is associated with an increased risk of falls and broken bones.
Specific consequences of sleep deprivation can include:
- mood changes
- anxiety
- depression
- challenges with memory
- focus and concentration difficulties
- impaired motor function
- fatigue
- weakened immune system
- weight gain
- high blood pressure
- insulin resistance
- chronic diseases, like diabetes and heart disease
- increased risk of early death
Sleep keeps us healthy and functioning well. It lets your body and brain repair, restore, and re-energize.
If you don’t get enough sleep, it can affect your memory, focus, immune system, and mood.
Most adults need 7 to 9 hours of sleep each night. If you’re having trouble sleeping, talk with a doctor or a sleep specialist. They can determine the underlying cause and help you improve the quality of your sleep.
