Human sleep occurs in periods of approximately 90 minutes, which include an increasing proportion of paradoxical (REM) sleep as they repeat. This rhythm is called the ultradian sleep cycle. Sleep proceeds in cycles of REM and NREM, usually four or five of them per night. The American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep. The whole period normally proceeds in the order: N1 ? N2 ? N3 ? N2 ? REM. In other animals the subdivision between phases of non-REM sleep is not typically used, although animal non-REM sleep can be described as lighter or deeper. There is a greater amount of deep sleep (stage N3) earlier in the night, while the proportion of REM sleep increases in the two cycles just before natural awakening.
Each stage may have a distinct physiological function and this can result in sleep that exhibits loss of consciousness but does not fulfill its physiological functions (i.e., one may still feel tired after apparently sufficient sleep).
When you’re scrambling to meet the countless demands of your day, cutting back on sleep might seem like the only answer. Who can afford to spend so much time sleeping, anyway? The truth is you can’t afford not to. Even minimal sleep loss takes a toll on your mood, energy, and ability to handle stress. By understanding your nightly sleep needs and what you can do to bounce back from chronic sleep loss, you can finally get on a healthy sleep schedule.
The power of sleep
Many of us try to sleep as little as possible. There are so many things that seem more interesting or important than getting a few more hours of sleep, but just as exercise and nutrition are essential for optimal health and happiness, so is sleep. The quality of your sleep directly affects the quality of your waking life, including your mental sharpness, productivity, emotional balance, creativity, physical vitality, and even your weight. No other activity delivers so many benefits with so little effort!
Sleep isn’t exactly a time when your body and brain shut off. While you rest, your brain stays busy, overseeing a wide variety of biological maintenance that keeps your body running in top condition, preparing you for the day ahead. Without enough hours of restorative sleep, you won’t be able to work, learn, create, and communicate at a level even close to your true potential. Regularly skimp on “service” and you’re headed for a major mental and physical breakdown.
The good news is that you don’t have to choose between health and productivity. As you start getting the sleep you need, your energy and efficiency will go up. In fact, you’re likely to find that you actually get more done during the day than when you were skimping on shuteye.
Myths and Facts about Sleep
Myth 1: Getting just one hour less sleep per night won’t affect your daytime functioning.You may not be noticeably sleepy during the day, but losing even one hour of sleep can affect your ability to think properly and respond quickly. It also compromises your cardiovascular health, energy balance, and ability to fight infections.
Myth 2: Your body adjusts quickly to different sleep schedules. Most people can reset their biological clock, but only by appropriately timed cues—and even then, by one or two hours per day at best. Consequently, it can take more than a week to adjust after traveling across several time zones or switching to the night shift.
Myth 3: Extra sleep at night can cure you of problems with excessive daytime fatigue. The quantity of sleep you get is important, sure, but it’s the quality of your sleep that you really have to pay attention to. Some people sleep eight or nine hours a night but don’t feel well rested when they wake up because the quality of their sleep is poor.
Myth 4: You can make up for lost sleep during the week by sleeping more on the weekends. Although this sleeping pattern will help relieve part of a sleep debt, it will not completely make up for the lack of sleep. Furthermore, sleeping later on the weekends can affect your sleep-wake cycle so that it is much harder to go to sleep at the right time on Sunday nights and get up early on Monday mornings.
Adapted from: Your Guide to Healthy Sleep (PDF) The National Institutes of Health
How many hours of sleep do you need?
According to the National Institutes of Health, the average adult sleeps less than seven hours per night. In today’s fast-paced society, six or seven hours of sleep may sound pretty good. In reality, though, it’s a recipe for chronic sleep deprivation.
There is a big difference between the amount of sleep you can get by on and the amount you need to function optimally. Just because you’re able to operate on seven hours of sleep doesn’t mean you wouldn’t feel a lot better and get more done if you spent an extra hour or two in bed.
While sleep requirements vary slightly from person to person, most healthy adults need between seven and a half to nine hours of sleep per night to function at their best. Children and teens need even more (see Average Sleep Needs table below). And despite the notion that our sleep needs decrease with age, older people still need at least seven and a half to eight hours of sleep. Since older adults often have trouble sleeping this long at night, daytime naps can help fill in the gap.
The best way to figure out if you’re meeting your sleep needs is to evaluate how you feel as you go about your day. If you’re logging enough hours, you’ll feel energetic and alert all day long, from the moment you wake up until your regular bedtime.
Sleep needs and peak performance
There is a big difference between the amount of sleep you can get by on and the amount you need to function optimally. Just because you’re able to operate on seven hours of sleep doesn’t mean you wouldn’t feel a lot better and get more done if you spent an extra hour or two in bed. The best way to figure out if you’re meeting your sleep needs is to evaluate how you feel as you go about your day. If you’re logging enough hours, you’ll feel energetic and alert all day long, from the moment you wake up until your regular bedtime.
Think six hours of sleep is enough?
Think again. Researchers at the University of California, San Francisco, discovered that some people have a gene that enables them to do well on six hours of sleep a night. This gene, however, is very rare, appearing in less than 3% of the population. For the other 97% of us, six hours doesn’t come close to cutting it.
Average Sleep Needs by Age
Newborn to 2 months old 12 – 18 hrs
3 months to 1 year old 14 – 15 hrs
1 to 3 years old 12 – 14 hrs
3 to 5 years old 11 – 13 hrs
5 to 12 years old 10 – 11 hrs
12 to 18 years old 8.5 – 10 hrs
Adults (18+) 7.5 – 9 hrs
Signs and symptoms of sleep deprivation and lack of sleep
If you’re getting less than eight hours of sleep each night, chances are you’re sleep deprived. What’s more, you probably have no idea just how much lack of sleep is affecting you.
How is it possible to be sleep deprived without knowing it? Most of the signs of sleep deprivation are much more subtle than falling face first into your dinner plate. Furthermore, if you’ve made a habit of skimping on sleep, you may not even remember what it feels like to be wide-awake, fully alert, and firing on all cylinders. Maybe it feels normal to get sleepy when you’re in a boring meeting, struggling through the afternoon slump, or dozing off after dinner, but the truth is that it’s only “normal” if you’re sleep deprived.
You may be sleep deprived if you…
- Need an alarm clock in order to wake up on time
- Rely on the snooze button
- Have a hard time getting out of bed in the morning
- Feel sluggish in the afternoon
- Get sleepy in meetings, lectures, or warm rooms
- Get drowsy after heavy meals or when driving
- Need to nap to get through the day
- Fall asleep while watching TV or relaxing in the evening
- Feel the need to sleep in on weekends
- Fall asleep within five minutes of going to bed
The effects of sleep deprivation and chronic lack of sleep
While it may seem like losing sleep isn’t such a big deal, sleep deprivation has a wide range of negative effects that go way beyond daytime drowsiness. Lack of sleep affects your judgment, coordination, and reaction times. In fact, sleep deprivation can affect you just as much as being drunk.
The effects include:
- Fatigue, lethargy, and lack of motivation
- Moodiness and irritability
- Reduced creativity and problem-solving skills
- Inability to cope with stress
- Reduced immunity; frequent colds and infections
- Concentration and memory problems
- Weight gain
- Impaired motor skills and increased risk of accidents
- Difficulty making decisions
- Increased risk of diabetes, heart disease, and other health problems
How sleep deprivation can add to your waistline
Ever noticed how when you’re short on sleep you crave sugary foods that give you a quick energy boost? There’s a good reason for that. Sleep deprivation has a direct link to overeating and weight gain.
There are two hormones in your body that regulate normal feelings of hunger and fullness. Ghrelin stimulates appetite, while leptin sends signals to the brain when you are full. However, when don’t get the sleep you need, your ghrelin levels go up, stimulating your appetite so you want more food than normal, and your leptin levels go down, meaning you don’t feel satisfied and want to keep eating. So, the more sleep you lose, the more food your body will crave.
Stages of sleep: REM sleep and non-REM sleep stages
All sleep is not created equal. Sleep unfolds in a series of recurring sleep stages that are very different from one another in terms of what’s happening beneath the surface. From deep sleep to dreaming sleep, they are all vital for your body and mind. Each stage of sleep plays a different part in preparing you for the day ahead.
There are two main types of sleep:
- Non-REM (NREM) sleep consists of three stages of sleep, each deeper than the last.
- REM (Rapid Eye Movement) sleep is when you do most active dreaming. Your eyes actually move back and forth during this stage, which is why it is called Rapid Eye Movement sleep.
The Stages of Sleep
Stage N1 (Transition to sleep) – This stage lasts about five minutes. Your eyes move slowly under the eyelids, muscle activity slows down, and you are easily awakened.
Stage N2 (Light sleep) – This is the first stage of true sleep, lasting from 10 to 25 minutes. Your eye movement stops, heart rate slows, and body temperature decreases.
Stage N3 (Deep sleep) – You’re difficult to awaken, and if you are awakened, you do not adjust immediately and often feel groggy and disoriented for several minutes. In this deepest stage of sleep, your brain waves are extremely slow. Blood flow is directed away from your brain and towards your muscles, restoring physical energy.
REM sleep (Dream sleep) – About 70 to 90 minutes after falling asleep, you enter REM sleep, where dreaming occurs. Your eyes move rapidly, your breathing shallows, and your heart rate and blood pressure increase. Also during this stage, your arm and leg muscles are paralyzed.
Understanding the Sleep Cycle
Quality sleep and your internal clock
Your internal 24-hour sleep-wake cycle, otherwise known as your biological clock or circadian rhythm, is regulated by processes in the brain that respond to how long you’ve been awake and the changes between light and dark. At night, your body responds to the loss of daylight by producing melatonin, a hormone that makes you sleepy. During the day, sunlight triggers the brain to inhibit melatonin production so you feel awake and alert.
Your internal clock can be disrupted by factors such as nightshift work, traveling across time zones, or irregular sleeping patterns—leaving you feeling groggy, disoriented, and sleepy at inconvenient times. The production of melatonin can also be thrown off when you’re deprived of sunlight during the day or exposed to too much artificial light at night—especially the light from electronic devices, including TVs, computers, tables, and mobile phones.
The architecture of sleep
You may think that once you go to bed, you soon fall into a deep sleep that lasts for most of the night, progressing back into light sleep in the morning when it’s time to wake up. In reality, the sleep cycle is a lot more complicated.
When you chart the sleep stages over the course of the night, the result looks like a city skyline—which is why it is called “sleep architecture”
During the night, your sleep follows a predictable pattern, moving back and forth between deep restorative sleep (deep sleep) and more alert stages and dreaming (REM sleep). Together, the stages of REM and non-REM sleep form a complete sleep cycle. Each cycle typically lasts about 90 minutes and repeats four to six times over the course of a night.
The amount of time you spend in each stage of sleep changes as the night progresses. For example, most deep sleep occurs in the first half of the night. Later in the night, your REM sleep stages become longer, alternating with light Stage N2 sleep. This is why if you are sensitive to waking up in the middle of the night, it is probably in the early morning hours, not immediately after going to bed.
Having a hard time getting up when your alarm goes off?
Even if you’ve enjoyed a full night’s sleep, getting out of bed can be difficult if your alarm goes off when you’re in the middle of deep sleep (Stage N3). If you want to make mornings less painful—or if you know you only have a limited time for sleep—try setting a wake-up time that’s a multiple of 90 minutes, the length of the average sleep cycle. For example, if you go to bed at 10 p.m., set your alarm for 5:30 (a total of 7 ½ hours of sleep) instead of 6:00 or 6:30. You may feel more refreshed at 5:30 than with another 30 to 60 minutes of sleep because you’re getting up at the end of a sleep cycle when your body and brain are already close to wakefulness.
The importance of deep sleep and REM sleep
It’s not just the number of hours in bed that’s important—it’s the quality of those hours of sleep. If you’re giving yourself plenty of time for sleep, but you’re still having trouble waking up in the morning or staying alert all day, you may not be spending enough time in the different stages of sleep.
Each stage of sleep in the sleep cycle offers benefits to the sleeper. However, deep sleep (Stage N3) and REM sleep are particularly important. A normal adult spends approximately 50% of total sleep time in Stage 2 sleep, 20% in REM sleep, and 30% in the remaining stages, including deep sleep.
The most damaging effects of sleep deprivation are from inadequate deep sleep. Deep sleep is a time when the body repairs itself and builds up energy for the day ahead. It plays a major role in maintaining your health, stimulating growth and development, repairing muscles and tissues, and boosting your immune system. In order to wake up energized and refreshed, getting quality deep sleep is essential. Factors that can lead to poor or inadequate deep sleep include:
- Being woken during the night by outside noise, for example, or in order to care for a crying baby.
- Working night shifts or swing shifts. Getting quality deep sleep during the day can be difficult, due to light and excess noise.
- Smoking or drinking in the evening. Substances like alcohol and nicotine can disrupt deep sleep. It’s best to limit them before bed.
Just as deep sleep renews the body, REM sleep renews the mind by playing a key role in learning and memory. During REM sleep, your brain consolidates and processes the information you’ve learned during the day, forms neural connections that strengthen memory, and replenishes its supply of neurotransmitters, including feel-good chemicals like serotonin and dopamine that boost your mood during the day.
To get more mind and mood-boosting REM sleep, try sleeping an extra 30 minutes to an hour in the morning, when REM sleep stages are longer. Improving your overall sleep will also increase your REM sleep. If you aren’t getting enough deep sleep, your body will try to make that up first, at the expense of REM sleep.
Paying off your sleep debt
Sleep debt is the difference between the amount of sleep you need and the hours you actually get. Every time you sacrifice on sleep, you add to the debt. Eventually, the debt will have to be repaid; it won’t go away on its own. If you lose an hour of sleep, you must make up that extra hour somewhere down the line in order to bring your “account” back into balance.
Sleeping in on the weekends isn’t enough!
Many of us try to repay our sleep debt by sleeping in on the weekends, but as it turns out, bouncing back from chronic lack of sleep isn’t that easy. One or two solid nights of sleep aren’t enough to pay off a long-term debt. While extra sleep can give you a temporary boost (for example, you may feel great on Monday morning after a relaxing weekend), your performance and energy will drop back down as the day wears on.
Tips for getting and staying out of sleep debt
While you can’t pay off sleep debt in a night or even a weekend, with a little effort and planning, you can get back on track.
- Aim for at least seven and a half hours of sleep every night. Make sure you don’t fall farther in debt by blocking off enough time for sleep each night. Consistency is the key.
- Settle short-term sleep debt with an extra hour or two per night. If you lost 10 hours of sleep, pay the debt back in nightly one or two-hour installments.
- Keep a sleep diary. Record when you go to bed, when you get up, your total hours of sleep, and how you feel during the day. As you keep track of your sleep, you’ll discover your natural patterns and get to know your sleep needs.
- Take a sleep vacation to pay off a long-term sleep debt. Pick a two-week period when you have a flexible schedule. Go to bed at the same time every night and allow yourself to sleep until you wake up naturally. No alarm clocks! If you continue to keep the same bedtime and wake up naturally, you’ll eventually dig your way out of debt and arrive at the sleep schedule that’s ideal for you.
- Make sleep a priority. Just as you schedule time for work and other commitments, you should schedule enough time for sleep. Instead of cutting back on sleep in order to tackle the rest of your daily tasks, put sleep at the top of your to-do list.
Getting enough sleep
- How to Sleep Better – Tips for Getting a Good Night’s Sleep
- How to Sleep Well As You Age – Tips for Overcoming Insomnia and Sleeping Better Over 50
- Sleeping Pills and Natural Sleep Aids – What’s Best for You? What You Need to Know About Sleep Aids and Sleeping Pills
- Reset Your Brain for Better Sleep – How Your Body Clock Affects Sleep