Circadian Rhythm - Timing of Sleep

circadian rhythm chart from wikipedia

Circadian Rhythm

The Circadian Rhythm is a 2 stage biological cycle that takes about 24 hours. This rhythm is simply a way of describing the patterns of activities that occur in the body over the course of an entire day. These are the body functions that must occur to keep an person alive. Controlling body temperature, brain waves, hormone production, and regeneration are all unconscious activities our body manages on our behalf.

Everything runs better on a schedule and the body is no different. The body schedules activities around its own internal clock, the circadian clock. The rhythms of the body are built-in, but are adjusted based on cues from the environment such as light and temperature, even the rotation of the earth. The body's reactions to light or the length of day is called Photoperiodism. It is probably the most important environmental cue the body can receive for its circadian clock. Even the space station has installed light systems to mimic the light cycle of a normal day to help the astronauts function well.

The normal circadian rhythm in humans is shown in the graphic above. There are several markers that are important to note. The first is the melatonin release during the evening to cue the onset of sleep. Melatonin is not present in detectable levels during the day time. The temperature of the body also begins to decline gradually through the night reaching minimum core body temperature about two hours before wake time. Other markers include changes in cortisol (stress hormone) levels and changes to the resting heart beat. If the circadian rhythm is interrupted for an extended period of time, health problems can arise. Changes to natural clock is linked to obesity, diabetes, and cardiovascular problems as well as a degradation in performance and awareness.

How to use the circadian rhythm to your advantage

Since we can control key environmental cues, we will use them to our advantage. The ones we can control, at least partially, are light, temperature, and sound. The body is designed to naturally wake and fall asleep on a schedule that until recently was controlled by the sun. Now with modern technology, shift work, and global markets, not everyone can live according to biology.

The key to consistent sleep is a consistent sleep schedule. Try sticking to the same bed time routine whenever possible. If you do the same activities every night (brushing your teeth, taking a shower, etc.), your will be training your body to fall asleep at a certain time. Over time the body will adjust and your wake times will also start to be consistent. Make sure to allocate the proper amount of time to sleep when selecting a bed time. The sleep calculator can help you select a time to wake or fall asleep.

You biggest enemy in falling asleep and staying asleep is going to be light. Try to sleep in a room where you can control how much light you are exposed to during your sleeping hours. The easiest would be to sleep in a windowless room but short of that, a safe best is to use blackout curtains. If changing the decor isn't an option you can try a sleep mask.

Technology is a double edged sword. The light from the various screens we look at in the evening for entertainment can confuse the circadian clock. The blue tinted light emitted can confuse the brain into keeping melatonin at the same levels as during the day. If you can, avoid using electronics about an hour or two before falling asleep. If you can't resist try using f.lux software to change the light spectrum on your computer or use sunglasses that filter blue light.

Most people sleep best at a temperature in the mid-60s to low 70s. One of events that occurs during sleep is a corresponding drop in body temperature. We can use both of these facts for decent sleep. We can control the temperature in the room with air conditioning. Most newer thermostats for a/c units are able to be programmed around your schedule. You can lower the temperature before bed time and then raise the temperature before you would wake. If you can't fiddle with the thermostat, have a fan blow air over the top your blanket to draw heat away. If you can, position the fan so that it blows horizontally over only the blanket portion to avoid the air drying your throat out during the night.

If you are having trouble falling asleep, you can fake your body into triggering sleep by lowering your core body temperature. The easiest method is a five minute cold shower just before getting into bed.

Sleep Cycles

Each sleep cycle consists of three NREM stages and one REM stage. The REM stage is when the body restores itself. This is also the stage where we experience dreams. Without enough sleep spent in the REM stage, the body will not be able to function as well as it should. This is the most important stage but it also occurs at the end of the sleep cycle.

The average adult experiences about four full sleep cycles per full night's rest. The first full cycle is about 90 minutes long. Each subsequent cycle averages 110 minutes.

Sleep Inertia

Sleep inertia is the physical state a person is in after an abrupt awakening. The feeling of sleep inertia is best described as a general feeling of grogginess, depressed alertness, a decline in motor function, and is usually accompanied by a desire to return to sleep (hit the snooze button). These symptoms often interfere with the ability to perform tasks for a significant amount of time after waking.

Factors that can influence the length and severity of symptoms:

  • if the person is 10 - 30 minutes into a sleep cycle (slow wave sleep), the amount of sleep inertia felt is greater than waking at any other point in the cycle. Reaction time will be slowest awakened during this period.
  • waking during a period of natural body temperature decrease, which is the first half of a normal night's sleep (approx. 3.5 hrs in duration)
  • only taking a nap, following an extended period of being awake or if the person has sleep debt.

How we can use the sleep cycle to reduce sleep inertia

Since what the body needs is REM sleep, we need to try and make sure we get as much as possible. Try to wake naturally, if possible. If you are on a schedule in the morning, the only real option is trying to ensure that you don't wake before a cycle is completed. The sleep calculator can be used to find the appropriate amount of sleep and to help reduce the negative effects of waking on a schedule. Timing our sleep to wake between cycles will help us avoid (or at least reduce) sleep inertia and enable us to wake feeling refreshed.

Any remaining feeling of sleep inertia can be masked by consuming caffeine. The duration and severity of the symptoms felt can be reduced by exercise or other type of physical activity. Think about scheduling your exercise before you go to work.

Notice that the first sleep cycle takes 90 full minutes to complete. This means that for a restorative nap you need to be asleep for an hour and a half. Most mid day naps are for stress relief and last around an hour.

Sleep Apnea

Sleep apnea is a severe sleep disorder with grave consequences if left unmanaged. Sleep apnea is best described as a pause or cessation of breathing. Basically you repeatedly stop and start breathing. There is two types of apnea; central and obstructive(OSA). OSA is the more common form and what happens is the throat muscles or airway actually relax or collapse while sleeping. Central sleep apnea occurs because the brain fails to signal or activate the muscles for breathing while sleeping.


  • loud snoring(more likely in obstructive apnea)
  • not able to stay asleep
  • attention problems
  • morning headache
  • spouse or another person witnesses the pause in breathing while your asleep
  • abruptly awakening with shortness of breath
  • dehydrated

Diagnosis and treatment of sleep apnea is to say the least uncomfortable. The diagnosis of course see your family doctor and get referred to a sleep clinic for a sleep study. The sleep study consist staying at the clinic overnight. They basically hook you to a bunch of machines and you are expected to sleep so they can monitor to see how many times you quit breathing. There is home sleep tests that your doctor may want to use. Your doctor may also refer you to a ear nose and throat doctor to rule out any kind of blockage. As for treatments of mild sleep apnea if you want to try to treat at home lose weight, no alcohol, stop smoking, avoid sleeping on your back. More commonly used treatment is a CPAP machine (Continuous Positive Airway Pressure) which is a mask worn over your nose and/or mouth as you sleep. The mask is hooked to a machine the continuously delivers air in to your nose which helps keep your airway open. This is believed by many to be most effective treatment. You may also want to try a dental device specifically designed to help keep airway open. If you have enlarged tonsils, smaller lower jaw with overbite, or deviated septum you may possibly need surgery.

Effects of Sleep Deprivation - Performance Destruction

Sleep deprivation is the collection of symptoms that occur due to lack of sleep over a period of time. Some of the more obvious side effects are fatigue, drowsiness, clumsiness, and weight loss/gain. Brain and cognitive function are adversely affected. Inhibition of growth, healing, and memory are some more physiological effects of sleep deprivation. If deprived of sleep for an ongoing period of time, it is possible to accumulate sleep debt. The is where the body is not getting enough sleep to repair itself and can cause physical, emotional, and mental fatigue. Many countries have used sleep deprivation as a very useful interrogation technique for a reason.

Most people experience partial sleep deprivation, or partial sleep restoration, which occurs when the individual doesn't get a full nights rest of a consistent basis. Partial sleep deprivation has been shown to reduce attentiveness and vigilance. This type of sleep deprivation is what causes reduced productivity and errors, but can more importantly can lead to accidents that injure and take lives. Contrary to popular belief, burning the midnight oil only leads to increased profits in the short term or help you complete hit that major deadline on a delivery for a few days. After that, the person is unable to think clearly which just causes more problems than solutions. Research has shown that sleep deprived mice have a build up a beta amaloid proteins in the brain which have been shown to reduce memory recall and formation as well as been linked to increased risk of dementia.

Absolute absence of sleep in humans is impossible due to microsleeps. Microsleeps occur when there has been a significant amount of sleep deprivation. A person brain will automatically shut down anywhere from one second to thirty seconds. A person is not consciously aware they are happening.

sources: - Mortality Associated With Sleep Duration and Insomnia

Oversleeping - It may be as bad as not getting enough sleep

Sleeping more than eight and half hours a night has been associated with a 15% increase in mortality and morbidity risk. Oversleeping has also been linked with depression, diabetes, obesity and heart disease. Notice, the word linked is used here as correlation does not equal causation. Getting more the recommended amount of sleep doesn't mean you will get diabetes and die but it may indicate some other problem.

Your body will wake when it has reached the amount of sleep needed. The important part is actually getting up immediately and going about your day. It is real easy to look over at the clock see that you can sleep another hour or two and it not interfere your schedule. This is actually not healthy and often times the body feels worse that you would have just got up the first time.

Don't be overly concerned if you need to sleep longer than eight hours a night, but consider why you may be sleeping more than the average person. Every person has their own sleep needs based on health, age and other genetic factors. Illness may cause you to sleep longer than normal to recover so just keep in mind sleeping 8 hours or even 10 won't kill you, but may indicate you have another health problem that may cause other issues going forward. If you are oversleeping on a consistent basis, it may be prudent to consult your doctor to see if there may be any undiagnosed health conditions that need to be addressed.


Insomnia and It's Causes

Insomnia or sleeplessness is a sleep disorder in which a person either has a problem falling asleep or staying asleep. By definition insomnia is difficulty initiating, maintaining sleep, or both. Insomnia may be due to the lack of quality of sleep or from the quantity of sleep. Insomnia is not a disease or a diagnosis; it is a symptom. The length insomnia can last varies. It can be short or long term and has no age preference although is more common in the elderly. There also may be a correlation between insomnia, depression, and anxiety. There are three types of insomnia:

  1. Transient insomnia lasts less than a week and is very similar to sleep deprivation. It can be the result of depression, high stress,
  2. Acute insomnia is the inability to consistently sleep well for a period of less than thirty days. It is also known as stress related insomnia or short term insomnia.
  3. Chronic insomnia can last longer than thirty days and can be the primary disorder or the result of another disorder. Some side effects are mental fatigue, muscle fatigue, and or mental fatigue. People with high levels of stress hormones are more prone to chronic insomnia.

Dreams and REM Sleep

A dream is the experience of envisioned images, sounds, or other sensations during sleep. Dreams are successions of emotions, ideas, sensations and images that occur during REM (rapid eye movement) sleep. Dreams can last a few seconds or up to twenty minutes. Some substances are known to interfere with REM sleep, can cause some people to not experience dreams often. On average a person has three to five dreams per night. Some scientists believe that all mammals have dreams but there is no way of knowing for certain. Dreams have been speculated on religiously, scientifically, and philosophically throughout history. Opinions on dreams have differed throughout history dating all the way back to Mesopotamia. One of the most influential experts on the subject is Sigmund Freud. Freud wrote broadly on dream interpretation in the form of psychoanalysis and dream theories. He believed that dreams are manifestations of our frustrated desires and anxieties to repressed childhood obsessions or memories.

Health and Restoration

The body needs sleep to recover from damage and exhaustion from the waking hours. During sleep the body enters a state in which healing is accelerated and toxins are flushed from the body. This is why one of the keys to growing muscle from body building is rest. Toxins are also flushed from the brain by spinal fluid but this only occurs when asleep. If these toxins are allowed to accumulate in the mind (from sleep deprivation for instance), the person would have a functional capacity similar to when intoxicated. These symptoms are reduced reaction time, coordination, mental acuity and confusion is not uncommon. Sleep is also shown to be necessary to memory retention. Don't stay up late to cram! Not only will your capacity to perform mentally be reduced the next day, but your probably won't remember as much as you are hoping.