How much sleep do I need?
Sleep needs differ among individuals and change with a variety of factors including age, mental and physical health and sleep debt. Within a 24-hour cycle, the average sleep needed is:
- children -- 9 hours
- adolescents (13-24 years old) -- 9.25 hours
- adults -- 8 hours
- seniors – 9.25 hours
What causes sleep and wakefulness?
Sleep and wakefulness are caused by a two-part physiological system.
- The suprachiasmatic nuclei is a cluster of nerve cells in our brain that serves as a clock and calculator, keeping track of how long we have been awake and calculating how much sleep we must get to restore ourselves. On average, most people need 1 hour of sleep for every 2 hours that they have been awake.
- However, most people are not physically able to be awake for 2 hours, sleep for 1 hour and repeat this cycle continuously. This is caused by a second system in our brains, which provides alertness by creating “jolts” of wakefulness throughout the day. This process allows us to stay awake and sleep for extended periods of time, creating an average pattern of 16 hours awake and 8 hours asleep.
- The suprachiasmatic nuclei is constantly creating a sense of “tiredness” in our bodies, while the jolts of alertness prevent us from feeling it throughout the majority of our day. After we’ve been awake for 14-16 hours, these jolts become less strong, allowing the feeling of being tired to set in and allow us to go to sleep.
Each person’s body needs a specific amount of sleep to maintain health and to prevent feeling tired. A cluster of cells called the suprachiasmatic nuclei keeps careful track of the amount of sleep we get. If we need 8 hours of sleep, but only get 7 on a particular night, these cells register that we “owe” an additional hour of sleep. This is our sleep debt. The amount of sleep “owed” is added to the amount of sleep our suprachiasmatic nuclei wants us to have each night. In this example, we will need to get 9 hours of sleep tonight to make up for the 1 hour we missed last night.
Over time, we can build up a significant amount of sleep debt. For example, if our bodies need 9 hours of sleep, but we only get 6 hours Monday through Friday, we build up a sleep debt of 15 hours. When Saturday rolls around, we may try to “catch up on sleep,” but to do this we would need our nightly 9 hours, plus the 15 hours to “pay off” the sleep debt, thus bringing us to a sleep need of 24 hours. Most people are unable to sleep for this much time due to the alerting system of our brain. Even if we can get 12 hours of sleep, we will still be holding onto another 12 hours of sleep debt. This results in us still feeling tired after getting “a good night’s sleep.”
Researchers are not sure what happens to sleep debt in the long term (meaning sleep debt that has accumulated for more than a year). However, in the short term (6-12 months) the only way to feel less sleepy is to “pay back” the sleep that you have missed.
Night owls vs. morning larks
You may notice that you feel more energetic in the evening than you feel in the morning, or vice versa. You also many notice that this changes over time. While part of energy surge may be due to conditioning yourself to a certain lifestyle (for example, if you have to get up at 6 am for work, you may “learn” to be energetic in the morning), it is primarily due to a biological programming sleep researchers call The Night Owl/Morning Lark Process.
Night Owls have more energy and feel more awake in the evening. In fact, even if a Night Owl wakes up early and feels tired throughout the day, they generally experience a “second wind” in the evening, making it extremely difficult, if not impossible, for them to fall asleep early. Morning Larks have opposite experiences: they feel most energetic and awake in the morning and if they go to sleep late the night before, “sleeping in” is nearly impossible.
While it is still unknown exactly which part of the brain controls this, it has been determined that the process is biological. It also tends to change over time: children tend to have more energy and get sleepy earlier in the evening than adolescents, who can stay awake late into the night or early morning but have a very hard time waking up when their alarm goes off for school. In fact, because of school schedules and the Night Owl Process in high school and college students, these populations are believed to have the largest amount of sleep debt.
What influences sleep?
In addition to the biological aspects that control sleep and wakefulness, sleep can also be influenced by:
Alcohol - Studies show that alcohol may cause you to feel tired and fall asleep faster, but it prevents you from reaching deep sleep, thus preventing the restorative processes of sleep from occurring.
Physical Health - Illness and injury may cause you to feel tired and require more sleep to heal. However, pain or symptoms of illness can also distract our bodies from sleep.
Mental/emotional health - Feelings of worry, stress, depression, or anxiety may make our minds feel like they are racing and prevent us from sleeping. Excitement can have the same effect.
Environment - The physical surroundings of the place you are sleeping can affect your ability to sleep. This can include a roommate or partner’s sleep habits or snoring, outside noises, the temperature of the room and light.
Sleep disorders - While almost everyone experiences some kind of sleep abnormality once in a while (such as feeling worried and not being able to fall asleep), some people have a biological sleep pattern abnormality. These disorders include sleep apnea, insomnia, teeth-grinding, breathing disorders that present while sleeping such as snoring, narcolepsy, emotional disorders such as night terrors and nervous system disorders such as restless leg syndrome among others. If you suspect that you many have a sleep disorder it is important to get medical treatment.
Sleep is extremely important to a person’s overall state of health. When we get enough sleep, we are happier, healthier, more focused and significantly safer than we are when we are carrying around sleep debt. This is because, while we sleep, we turn off the more “active” physical processes of our bodies, such as moving and thinking and allow the passive processes, like cellular restoration, to take over. Some highlights of this restorative process include:
- Stress management: after a good night's sleep, a project that seemed impossible the day before may seem much more manageable.
- Physical restoration: next time you get a paper cut on your finger, look at how much it heals while you sleep. The same kind of physical restoration happens to every cell in your body while you sleep.
- Learning: during the day, your brain receives information that goes into short-term memory. While you sleep, some of this information is integrated into long-term memory and understanding. Sleep Well!
Tips for Restful Sleep
- Create a bedtime routine. Your body will learn that doing things in a certain order means that it’s time to “turn off,” relax and fall asleep. For example, organize your materials for the next day, take a shower, check your alarm and get into bed.
- Set a bedtime and wake-up time and stick to it regularly (weekdays and weekends) as best as possible. Of course, if you develop a sleep debt, allow yourself the time to “pay it off.”
- Use your bed ONLY for sleep, rest and intimacy. Teach your body to associate your bed with these activities, rather than work and study. If you lay down to go to sleep, but your body sees your bed as a place to think, you might find it hard for your brain to shut down. The opposite could be true too: if your body understands that beds are for sleeping in, you may find yourself asleep on your books if you try to study there.
- Limit caffeine and sugar intake, particularly later in the day.
- Get physical activity daily; it will help you burn off excess energy and manage stress that may keep you up at night.