The average adult needs between 7 to 9 hours of sleep every night, an amount equivalent to over a third of one’s entire lifespan. Why do we need so much sleep to live a healthy life? Answering this question requires a deep appreciation of how sleep works, and how those mechanisms relate to the health benefits that sleep provides. From that understanding, we can then determine how best to leverage the inner workings of sleep to ensure a good night’s rest. The payoff: when sleep quality is high, consistently, the risks of long-term mental health and metabolic disorders are reduced. 

How does sleep work?

A good night’s sleep is not just a single phase of unconsciousness that you enter before waking up in the morning. Rather, sleep is divided into two phases that cycle throughout the night: 

• Rapid eye movement (REM) sleep begins about an hour and a half after you fall asleep. REM sleep is characterized by several bodily changes, including a temporary loss of muscle tone, darting eyes underneath closed eyelids, irregular breathing, and twitching limbs.
  
• Non-rapid eye movement (NREM): NREM sleep constitutes the restful phase of sleep. Here, a person’s brain activity, breathing, and heart rate slow down to facilitate the transition into deep sleep.

NREM sleep is also further divided into three stages that are cycled alongside the two phases:

• The N1 stage lasts only one to five minutes. It acts as a transitory stage of rest, featuring light changes in brain activity accompanied by periodic muscle twitches. While a sleeping person can be woken up easily in this phase, they can also quickly transition into the other two stages of NREM sleep.
  
• After exiting N1, a person will enter Stage N2. Usually lasting 30 to 60 minutes each cycle, your body will begin to reduce its body temperature and continue lowering its heartbeat, breathing, muscle activity, and eye movement.
  
• The N3 stage is the final and deepest stage in NREM sleep. Here, your body will have the lowest physical activity. Your body’s activity is so low that if you are awoken during this stage of sleep, you’re likely to demonstrate mental fogginess for up to an hour before recovering full mental faculties. 

What happens to your body when you sleep

The complexities of sleep have spurred researchers onward to study the physiological processes that happen to your body when you sleep. 

• Scientists can monitor the electrical activity produced by your brain through a specialized machine called an electroencephalograph (EEG). These efforts have enabled researchers to identify three distinct sets of brain signals produced in NREM sleep. Two of these signals are generated in the N2 phase of NREM sleep. The first of these, sleep spindles, are small, waxing-and-waning signals that last a few seconds. Conversely, K complexes — generated spontaneously or in response to weak auditory stimuli — are the largest of these waves. The last of these signals produced are called delta waves. Produced during the N3 phase, delta waves are smoother than K complexes and reflect the deep sleep nature of this phase.
  
• Sleep is a critical part of your body’s circadian rhythm, the primary behavioral regulator of your sleep-wake cycle. Your circadian rhythm enables you to respond to diverse environmental cues, particularly light, to let you know when to stay awake or to prepare for sleep. In the absence of light, your body produces melatonin, a hormone that helps you prepare to sleep. As you sleep, your body also releases other hormones that help maintain normal body structure and metabolism, such as growth hormone and thyroid hormone. 
  
• The rest of your body also changes its behavior as you doze off to sleep. Your lungs take fewer breaths, with the occasional increase while in the REM phase. While your heart also reduces its heart rate during sleep, your heart rate can also fluctuate depending on the dreams you experience.  

Benefits and risks of adequate sleep and sleep deprivation

As discussed above, your body undergoes many physiological changes that help you get the night’s rest you need. Even so, the perception of long periods of inactivity may cause people to adopt negative attitudes toward sleep that reduce sleep quality. However, we can not state enough the importance of having a good night’s sleep. Sleeping well at night provides a host of health benefits:

• Mental development and cognition: Your brain produces electrical signals as slow oscillating waves while you sleep. Sleep spindles generated during the N2 stage have the strongest correlation with improved cognitive function. The frequency of these spindles is also associated with enhanced neurocognitive development in children.
  
• Mental health: A good night’s rest also provides benefits for your mental health. A 2021 systematic review of 65 trials identified a dose response relationship in which greater improvements in sleep further improved mental health.
  
• Metabolic health: A good night’s rest also helps you maintain a healthy metabolism. A 2020 systematic review of 41 eligible studies determined that people with healthy sleep patterns were more likely to have healthier metabolic outcomes. These benefits, however, cannot be fully reaped unless you maintain a consistently healthy sleep schedule. A 2016 study of 338 women determined that those who had higher variability in bedtime and longer bedtime delays were at greater risk of insulin resistance.

Disruptions can come in many forms, such as sleep restriction, sleep fragmentation, and disrupted sleep patterns. Each of these perturbations increases the risk of disease:

• Obesity: Disruptions to your sleep can increase the risk of metabolic disease. In support of this, a 2021 systematic review and meta-analysis of 13 studies determined that both excessively short and long sleep can increase the risk of high blood pressure, obesity, and high blood sugar levels.
  
• Type 2 diabetes (T2D): Not having a good night’s rest also increases the risk of dysregulated blood sugar levels. A 2022 systematic review of 35 studies determined that altered sleep timing and reduced sleep quality increase T2D risk by reducing insulin sensitivity. These risks also manifest themselves among people having too much sleep, as a 2018 meta-analysis of 137 prospective cohort studies determined.
  
• Cardiovascular disease (CVD): The quality of your sleep can also affect the risk of getting CVD. A 2018 meta-analysis featuring 30 eligible studies determined that those whose sleep durations diverged from the recommended 7 to 8 hours had a greater risk of experiencing cardiovascular events and mortality. The risk of cardiovascular stress also applies to children. A 2021 systematic review of 68 studies concluded that school-aged children who had sleep disturbances were more likely to have levels of stress biomarkers that reflect immune, cardiovascular, and metabolic stress.

How to get a good night’s sleep

With the myriad benefits and risks that come with adequate sleep and sleep disruptions, respectively, the importance of having a good night’s sleep should not be ignored. Here are some suggestions that you can implement to ensure a good night’s rest:

• Establish a consistent sleep routine: Adopting the same sleeping hours every day helps your body establish a habit that reinforces your body’s circadian rhythm. A healthy sleep routine reduces the risk of insomnia among elderly men. A consistent sleep schedule is also associated with healthy body composition among elderly women.
  
• Reduce blue light exposure in your electronic devices: Your cellphones and electronic devices emit a substantial amount of blue light. During the day, exposure to blue light improves attention span by increasing the activity of your prefrontal cortex. At night, however, exposure to blue light can disrupt your circadian rhythm and sleep by increasing alertness and reducing the release of melatonin. Search for programs that reduce blue light exposure or turn off your devices a half hour before you sleep.
  
• Secure a healthful diet throughout the day: A healthful diet plays a vital role in getting you a good night’s rest. For instance, adopting a Mediterranean diet correlates with improved sleep quality.
  
• Limit alcohol consumption: Although it may help you enter sleep, drinking alcohol before bed increases the risk of sleep disruptions and insomnia.
  
• Adopt a consistent exercise routine: Finding healthy ways to keep your body active also helps you get a good night’s rest. Having moderate to vigorous exercise for at least 2.5 hours per week helped insomnia patients improve their sleep in a 2015 randomized control trial (RCT) of 41 insomnia participants.

Key takeaways

Sleep provides an important opportunity for daily, prolonged rest from the everyday grind of life. But sleeping is not merely a single-step process. Rather, sleep occurs as a complex cycle of phases and stages that help your body regain the energy it needs to go about the next day. Establishing a healthy, habitual sleep routine also provides long-term mental health and metabolic benefits that increase your longevity and well-being. Despite its importance, almost half of all Americans fail to get a good night’s rest — even though there are relatively easy, straightforward ways to improve sleep. Exercising, adopting a healthy diet, and limiting the use of electronic devices are three of the more effective practices that can help you find peace in a good night’s sleep again.