Sleeping fewer than 7 hours in every 24 hours is classified as short sleep duration.
In the United States, there is concern that many people are not getting enough sleep. This has been linked to factors such as shift-work, multiple jobs, and spending time watching television and using the Internet.
Fast facts about sleep
- How much sleep we need depends on individual requirements, including age.
- Sleep affects our performance, mood, and general health.
- Sleep deprivation has been linked to long-term adverse effects on health, and a higher risk of premature death.
- Most tips for a good night’s sleep are based on good routines.
- Many sleep disorders lead to excessive daytime sleepiness, difficulty falling or staying asleep, or abnormal events during sleep.
Sleep in adults
The following amounts of sleep are recommended in every 24 hours, depending on the age group:
- From 18 to 60 years: 7 hours or more
- From 61 to 64 years: 7 to 9 hours
- From 65 years: 7-8 hours
However, the amount of sleep a person needs will depend on how they feel and their productivity.
Feeling sleepy or depending on caffeine during the day, for example, may signal insufficient or poor quality sleep.
As we grow older, the structure of the sleep pattern, called “sleep architecture,” changes considerably.
These changes affect:
- how we fall asleep and stay asleep
- how much time we spend in each stage of sleep
- how well we start sleeping and stay asleep
The overall amount of sleep and sleep efficiency both tend to decline with age. As we age, we tend to wake earlier and go to bed earlier.
People aged 65 to 75 years, for example, typically wake up 1.33 hours earlier and go to bed 1.07 hours earlier than those aged 20 to 30 years.
Decreases in melatonin synthesis in older adults have been linked to sleep disorders and a range of adverse health conditions.
Melatonin is the neurohormone produced in response to diminishing light levels at dusk. Levels drop in the early morning before we wake.
Shift work, overseas travel, aging, and other facts can affect melatonin synthesis. This can then disrupt sleep patterns and sleep quality.
Sleep in children
The Centers for Disease Control and Prevention (CDC) suggest that infants, children, and teenagers need the following sleep in every 24 hours:
- Up to 3 months of age: 14 to 17 hours
- From 4 to 12 months: 12 to 16 hours
- From 1 to 2 years: 11 to 14 hours
- From 3 to 5 years: 10 to 13 hours
- From 6 to 12 years: 9 to 12 hours
- From 13 to 18 years: 8 to 10 hours
Newborns do not have an established circadian rhythm. The circadian rhythm and need to sleep more during the night rather than the day as part of a 24-hour cycle develop from the age of 2 or 3 months.
Young infants do not have long, continuous episodes of sleep. Instead, they sleep for 16 to 18 hours a day for short periods of between 2.5 and 4 hours.
By the age of 12 months, sleep patterns develop that involve less sleep and is concentrated more around the nighttime.
The infant also loses a feature of infant sleep known as active sleep, in which there is a lot of body movement. Instead, muscle paralysis with atonia takes place during REM sleep.
Physiological needs, cultural environment, and social changes, such as reduced daytime napping and school routines, mean that the amount of sleep children get progressively decreases into adolescence.
Research about alertness, sleep-wake cycles, hormones, and circadian rhythms indicates that adolescents, as determined by puberty rather than only age in years, need up to 10 hours of sleep every night.
However, over two thirds of high school students say they get less than 8 hours on school nights.
Pregnancy increases the need for sleep, especially in the first trimester. There may also be more daytime sleepiness, which can continue throughout first few months after giving birth.
This is thought to be in part due to the effects of the hormone progesterone, which increases during pregnancy.
Restless legs syndrome (RLS) is more likely to occur during pregnancy, as are snoring, strange dreams, and insomnia. These can affect the quality of sleep.
The following tips may help promote sleep during pregnancy:
- Sleep whenever and wherever possible.
- Take daytime naps when needed.
- Sleep on the left side to improve the flow of blood and nutrients to the fetus.
- Drink less fluid before bed and, if woken, go to the toilet at night.
- Reduce sleep disturbance by avoiding putting on bright lights.
Why we sleep
We need sleep to feel rested and to function in our daily lives. We know that sleep loss can have serious consequences, but exactly why we sleep is not fully understood.
Studies of the effects of sleep deprivation show that a lack of sleep can affect our:
- overall health
Sleep contributes to the proper functioning of the nervous system, including cognitive abilities and emotional health.
Sleep deprivation can decrease alertness and reduce response times. One way to think about this would be the feeling of being drunk, when your ability to drive or operate heavy machinery would be altered, which occurs after not having any sleep for 24 hours straight.
Brain imaging has shown that pathways for memory and learning are active during certain sleep stages. We need sleep for clear thinking, normal reactions and the creation of memories.
Emotional and social functioning may depend on good sleep, and mood is affected by deprivation. Not sleeping enough may increase the risk of depression.
Sleep enables the body to produce hormones essential to childhood growth and development and health maintenance in adults.
These hormones help the body to:
- build muscle
- fight illnesses
- repair damage
High blood pressure, heart disease, and other adverse medical conditions may be more likely if sleep is poor in quantity or quality.
Sleep also appears to promote metabolism and energy use. Poor sleep has been linked to weight gain, obesity, diabetes mellitus, and poorer dietary choices.
Obesity and being overweight also increase the risk of obstructive sleep apnea. This disrupts sleep and can make it harder to lose weight.
What happens during sleep
Sleep scientists have separated sleep into two types through which we cycle alternately:
- rapid eye movement (REM) sleep, accounting for 20 to 25 percent of sleep
- non-rapid eye movement (NREM) sleep, accounting for 75 to 80 percent of sleep
These can also be broken down into smaller stages.
One way of describing the stages of sleep is as follows:
Stage 1, NREM sleep: This stage lasts several minutes, and it involves the change from being awake to being asleep. Sleep is light, and the brain waves, heartbeat, breathing, and eye movements slow down. Muscles relax, but they may twitch at times.
Stage 2, NREM sleep: More repeated sleep cycles are spent in this stage than in any other stage. This is a time of light sleep, before entering a deeper sleep. Heartbeat and breathing slow down, muscles relax further, eyes stop moving, and body temperature falls. Brain activity slows but with occasional bursts of activity.
Stage 3, NREM sleep: This deep sleep time is needed to feel refreshed during the day. Longer periods of deep sleep tend to occur in the first half of the night. Heartbeat and breathing rates are the slowest while asleep here, and brain activity slows right down, and muscles are relaxed.
REM sleep: The first cycle of REM sleep is around 90 minutes after falling asleep. The eyes are closed, but the pupils move quickly from side to side. Breathing and heart rate speed up, the blood pressure rises, and brain activity is mixed. Arm and leg muscles can become paralyzed.
This may be to prevent the acting out of dreams, although it has been suggested that this might also help decompress the intervertebral discs by relaxing the muscles and supporting structures that normally keep the spine rigid.
Other physiological changes affect:
- the cardiovascular system
- sympathetic nerve activity
- breathing rate
- blood flow to the brain
- urine flow, due to changes in kidney function
- hormone levels, including thyroid hormones, melatonin, and growth hormones
Body temperature also tends to be lower at night.
Why do we dream?
We may dream for over 2 hours each night, although we may not remember our dreams.
Dreaming, or at least REM sleep, may help us process our emotions.
Investigations have found that learning and memory appear to improve with adequate NREM and REM sleep.
Dreaming mostly occurs during REM sleep, but it can happen in early NREM sleep stages as well. Memory consolidation probably happens in both types of sleep.
Adults are considered to have sleep deprivation when they get less than the average need for 7-9 hours sleep a night.
Insufficient sleep in the U.S. is considered a public health problem.
Between 50 and 70 million Americans are thought to have some kind of sleep disorder.
The long-term effects of cumulative sleep loss include an increased risk of:
- hypertension, or high blood pressure
- diabetes mellitus
- heart attack
Humans can bear not sleeping for several days, but with a negative impact on functioning, including:
- reduced concentration
- visual disturbances
- slower reactions
- memory problems
- emotional disturbances
- unclear speech and difficulty communicating
- increased sensitivity to pain
Impaired judgment due to sleep loss can lead to poor decision making and road traffic accidents.
Sleep medicine specialists have identified over 100 distinct sleep disorders.
Most have one of the following features:
- excessive daytime sleepiness
- difficulty getting to sleep or staying asleep
- abnormal movements, behaviors or sensations during sleep
Separate medical conditions can also adversely affect sleep, such as pain, infection, chronic obstructive pulmonary disease, obstructive sleep apnea, and peptic ulcer disease.
Circadian rhythm sleep disorders include the effects of jet lag and shift work.
Parasomnias are unpleasant or undesirable sleep behaviors or experiences, including disorders of arousal, which may involve disoriented sleepwalking, shrieking, or flailing limbs.
Tips for a good night’s sleep
Sleep hygiene refers to a routine that promotes good sleep.
Here are some tips:
- Keep to the same sleeping and waking times, including at weekends.
- Set a bedtime for when you will feel sleepy and that will leave at least 7 hours for sleeping.
- Avoid daytime naps that reduce bedtime sleepiness.
- Avoid alcohol, caffeine, tobacco smoking, and heavy meals before bedtime.
- Establish a regular winding down ritual, which could include a bath, reading or meditation.
- Try to avoid tension before sleeping for example, heated discussions.
- Avoid watching TV, browsing the Internet, and so on, before bedtime, and do not do these activities in bed.
- Keep the bedroom quiet, dark, and cool, with comfortable bedclothes.
- Use your bed only for sleep and sex.
- If you cannot sleep after 20 minutes of trying, reduce the association with an inability to sleep by going to another room and read in a chair until you feel sleepy.
- Exercise may be beneficial for sleep. Do vigorous exercise during the day and relaxing exercise, such as yoga, before bed.
Many of these sleep hygiene practices may help the body to regulate melatonin synthesis properly.
As natural light levels fall at dusk, the pineal gland produces and secretes melatonin, prompting the body to prepare itself for sleep.
Use of artificial light, including the light emitted by televisions, phones, and computers, can trick the brain into thinking it is still daylight. This may inhibit melatonin synthesis and delay sleep.
People who are unable to entirely cut out screen-time after dusk may find it helpful to use specific software on screens to filter out blue light in the evening.
Other tips for helping people to fall asleep include:
- listening to relaxing music or meditations while falling asleep
- using essential oils, such as lavender
- using nasal strips to reduce snoring
- drinking chamomile tea
A number of products are available to purchase online. Many of these have not been confirmed by research to be effective, but they may be worth a try.
Supplements containing chamomile, valerian, and melatonin are sold to help with sleep, but more evidence is needed to support their use. They should not be taken without first asking a doctor if they are safe for you to use, as they may interact with other drugs.