The Science of Sleep: Why You Need 7 to 8 Hours a Night

Why do we need sleep?

People who can get by on four hours of sleep sometimes brag about their strength and endurance. But recent scientific studies show that a lack of sleep causes many significant changes in the body and increases your risk for serious health concerns such as obesity, disease, and even early death.
Sleep is an important function for many reasons. When you sleep, your brain signals your body to release hormones and compounds that help:

• decrease risk for adverse health conditions
• manage your hunger levels
• maintain your immune system
• retain memory

But you can’t catch up or make up loss of sleep. In fact, consistently sleeping more than six to eight hours a night can negatively impact your health. Read on to learn why seven to eight hours of sleep a night is ideal.

Seven to eight hours for longevity

The healthy amount of sleep for the average adult is around seven to eight hours each night.
Researchers in the United Kingdom and Italy analyzed data from 16 separate studies conducted over 25 years, covering more than 1.3 million people and more than 100,000 deaths. They published their findings in a 2010 articleTrusted SourceTrusted SourceTrusted Source.
Those who generally slept for less than five to seven hours a night were 12 percent more likely to experience a premature death. People who slept more than eight or nine hours per night had an even higher risk — 30 percent.
Researchers also found that people who reduced their nightly sleep time from seven to eight hours to below seven hours were at an increased risk of death from all causes. Additionally, the researchers also saw an increased risk of death from all causes in those who slept for a long amount of time per night.

Sleep helps manage your appetite

Poor sleep habits can increase the body’s energy needs. At night, movement and the need for calories is reduced. But when you are sleep-deprived, your brain will release chemicals to signal hunger. This can lead to eating more, exercising less, and gaining weight.
Sleep deprivation also affects children. A 2014 study showed that children who slept less had an increased risk for obesity and high BMI. These risks can affect children as they mature.

Sleep helps your immune system function

When you sleep, your immune system releases compounds called cytokines. Some cytokines have a protective effect on your immune system by helping it to fight inflammation, including inflammation due to infection.
Without enough sleep, you may not have enough cytokines to keep you from getting sick. Other components of the immune system, like antibodies and white blood cells, can be reduced over time without enough sleep.

A 2013 study found that sleep restrictions increase the amount of inflammatory compounds and activity in a person’s body. These are the same compounds associated with conditions like asthma and allergies.
The researchers studied people who underwent limited sleep deprivation of four hours a night for 5 days in a row. Before and after these 5 days of limited sleep deprivation, two nights in a row of 8 hours per night of sleep time were part of the experimental protocol utilized in the experimental group subjects.

In comparing their study subjects with limited sleep deprivation to other studies where the subjects had long-term sleep deprivation, the researchers found that the participants’ immune systems were affected regardless. Even with a short period of limited sleep deprivation, the immune system was affected in ways similar to those with long-term sleep deprivation.

Sleep helps your memory

In addition to helping you focus, sleep helps protect and strengthen your memory. Research shows that sleeping after learning can help with memory retention. Sleep is also thought to reduce interference from external events.
People who are sleep-deprived:

• have a harder time receiving information due to the brain’s overworked or fatigued neurons
• may interpret events differently
• tend to have impaired judgement
• lose their ability to access previous information

It’s important to get seven to eight hours of sleep so that you can experience all the sleep stages. No one stage is responsible for memory and learning. Two stages (rapid eye movement and slow-wave sleep) contribute to:

• creative thinking
• procedural memory
• long-term memory
• memory processing

Lack of sleep increases disease risk

Lack of sleep is known to be a contributing factor for many chronic health conditions, including:

• diabetes mellitus
• heart disease
• obesity
• obstructive sleep apnea

Sleep is a habit, just like eating healthy and exercise. While everyone misses a few hours of sleep sometimes, chronic lack of sleep is part of an unhealthy lifestyle and can increase your risk for serious health concerns.
Having a poor work-life balance, stress, and worry can all affect how much and how well a person sleeps. These kinds of stressors can lead to further inflammation and health problems in addition to lack of sleep.

How to get more sleep

The recommended seven to eight hours of sleep is mainly for adults, including older adults. Younger people may need more sleep. See the table below for the recommended amount of sleep by age.

Age	Recommended hours of sleep per day
Infants	16-18 hours
Preschoolers	11-12 hours
Elementary	at least 10 hours
Teens	9-10 hours
Adults (including seniors)	7-8 hours

Building good sleep habits

Are you among the many people getting fewer than seven hours of sleep per night? Try adopting some of these practices to help you sleep better and longer:
Schedule your sleep: Make an effort to go to bed and wake up at the same time every day of the week, including weekends. Doing this establishes a regular sleep-wake cycle. It may help you adopt the habit of doing the same things each night before bed, such as taking a warm bath or reading.

Avoid stimulants: Caffeine, chocolate, and nicotine can keep you awake past your bedtime. Alcohol may make you feel sleepy initially, but its effect eventually may disrupt your rest later in the night. Stay away from stimulants at least four hours before sleep.
Make your bed comfy: A number of new mattresses on the market are aimed at increasing comfort, including those that have “cooling” effects to keep a person from getting too warm while they sleep. Memory-foam mattresses conform to a person’s body, providing extra shape and support. Use room-darkening shades, earplugs, or other tools that will help create a restful environment.

Exercise regularly: Being physically active during the day can help you fall asleep faster at night. Exercise also helps to promote deeper, more restful sleep. Just make sure you don't exercise too close to bedtime, since this can leave you too energized to sleep.
Relieve stress during the day: Try adopting some stress-reducing techniques before bed. Keep a journal by your bedside to write down what's bothering you. Start practicing yoga, learn to meditate, get regular massages, or take long walks.
Apps for sleep: Some apps can help you sleep better. Sleep Genius tracks your sleep cycles and offers a progressive alarm clock to prevent sudden waking that’s associated with increased tiredness. Other apps, like pzizz, provide soft music and sounds used to encourage restful sleep.