*Nothing in this article constitutes medical advice. Seek the guidance of a physician if you have any questions.*
Every person on planet earth has at least one thing in common: sleep. Even though it is one of the most passive activities that humans partake in, sleep is required for normal and healthy brain function. Like water, it is a necessity that we can only go without for a few days at a time, at maximum.
One of the most interesting aspects of sleep is just how varied it can be. Different people have different relationships with sleep: some people get too little sleep, some wake up often during the night, some are drowsy during the day, and some sleep so normally they don’t even think about it. Beyond that, different people require different amounts of sleep. Some people can go to bed past midnight and wake up at 6 AM and seemingly be fine. Others feel groggy after 9 hours of rest.
While there is a large amount of variability between people, experts recommend specific amounts of sleep based on a person’s age. According to the National Sleep Foundation (NSF), individuals generally require less sleep as they age. Take a look at the numbers below.
- Newborns (0-3 months): 14-17 hours each day
- Infants (4-11 months): 12-15 hours
- Toddlers (1-2 years): 11-14 hours
- Preschoolers (3-5): 10-13 hours
- School age children (6-13): 9-11 hours
- Teenagers (14-17): 8-10 hours
- Younger adults (18-25): 7-9 hours
- Adults (26-64): 7-9 hours
- Older adults (65+): 7-8 hours
As we can see from above, regardless of age, every person needs to average at least 7 hours of sleep per night for optimal recovery. Depending on the age of the person, this sleep may come in bursts or all together. Let’s take a look at how sleeping habits change throughout our lives.
Understanding fetal behavior has posed a challenge to scientists for decades. As recently as the 19th century, in some parts of the world, the idea that babies could fall asleep for prolonged periods inside the womb was pervasive. Dr. Willy Jansen elaborates on this point, “According to this belief, the unborn child will remain dormant for an indefinite period of time until it is awakened… Pregnancies can, therefore, last much longer than the normal nine months… and birth can be delayed by as much as several years after conception.”
While modern science has discredited the notion that babies can “fall asleep for years,” we do know that fetuses do in fact sleep in the womb. The trick is understanding just how much they sleep. Because measuring brain activity is notoriously difficult in utero, researchers have largely focused on rapid eye movement (REM) as a means of determining fetal sleep cycles.
All humans undergo REM sleep. It is typically regarded as “deep sleep” and is marked by fast twitching and moving of the eyes. Recent studies have indicated that around 7 months, REM sleep is detected quite often in fetuses. By their estimation, “a human fetus spends most of its time asleep.” This is likely the time when a human will spend the most time asleep as a percentage of any given day.
As soon as birth occurs, sleep habits change drastically. Now, infants must be awake for periods of the day for one simple reason: food. While in the womb, fetuses receive oxygen and nutrients through the placenta, but, as soon as they’re born, require constant nourishment through breastmilk.
Any person who has raised a child (or been around through the process) may laugh at the concept of “sleep habits” in regards to infants. While it may seem like there is no rhyme or reason to when infants are awake or asleep, we do know that some things are consistent.
Generally speaking, newborns will sleep roughly ⅔ of the day sleeping: about 8 hours during the day and 8 hours during the night. Because a baby’s stomach is so small, they need to be constantly fed, usually every 3 hours. Due to this, infants typically won’t sleep through the night until they are at least 3 months old. This age can vary, though, and some infants don’t start sleeping through the night until they are around a year old.
Once children make it through the early developmental stages, sleep habits usually being to stabilize. As children grow older, then require less sleep, but the amount they need is still significantly more than older adults. According to the NSF, school-aged children still need a minimum of 9 hours of sleep. This is a large factor in the push to move school start times back, a concept that the Centers for Disease Control endorses.
As adults begin to be of full-time working age, they also begin to require less sleep. The average adult (18-64) usually does not need more than 9 hours of sleep a night – in stark contrast to adolescents that need a minimum of that much sleep. Unfortunately, middle age is when sleep problems begin to present. Conditions such as insomnia, narcolepsy, and sleep apnea are seen in much higher rates in adults. Any of these can cause 8 hours of uninterrupted sleep to be punctuated by periods of wakefullness and poor sleep quality.
Elderly individuals need the least amount of sleep for healthy recooperation. According to the NSF, seniors require only 7-8 hours of sleep. Compared to an adolescent, a 65-year old will likely spend 700 more hours awake per year! Research surrounding the root cause of this apparent lesser need for sleep remains fuzzy. Presently, the evidence seems to indicate that diminished need is due to significant changes in the circadian rhythms of geriatric individuals.