What controls our need for sleep?

Most people notice that they naturally experience different levels of sleepiness and alertness throughout the day. But what causes these patterns? Sleep is regulated by two body systems: sleep/wake homeostasis and the circadian biological clock.

When we have been awake for a long period of time, sleep/wake homeostasis tells us that a need for sleep is accumulating and that it is time to sleep. It also helps us maintain enough sleep throughout the night to make up for the hours of being awake.

Our internal circadian biological clocks regulate the timing of periods of sleepiness and wakefulness throughout the day. The circadian rhythm dips and rises at different times of the day. The strongest sleep drive generally occurs between 2:00-4:00 am and in the afternoon between 1:00-3:00 pm, although there is some variation depending on whether you are a “morning person” or “evening person.”

The sleepiness we experience during these circadian dips will be less intense if we have had sufficient sleep, and more intense when we are sleep deprived as determined by the sleep/wake homeostasis. The circadian rhythm also causes us to feel more alert at certain points of the day, even if we have been awake for hours and our sleep/wake homeostasis would otherwise make us feel more sleepy. The combination of sleep/wake homeostasis and the circadian clock forms the basis of what is known in sleep medicine as the two-process model. This is what explains the need for sleep in our daily lives.

How is our circadian clock set?

The timing of our internal circadian clock takes cues for synchronization to our daily schedule by “time givers.” By far, the strongest of these is light. Light in the morning prevents the circadian clock from becoming delayed while light in the evening may delay the circadian clock. The opposite is also true with regards to advancing the circadian clock. Less important time givers include meals, social interactions, and temperature.

Can the circadian clock be set wrong?

Circadian disruptions such as jet lag and shift work put us in conflict with our natural sleep patterns. These disruptions of time and light force the body to alter its normal pattern to adjust. This is why jet lag can leave travelers feeling poorly and having more difficulty thinking and performing well. These symptoms can also occur in everyday life, when the circadian rhythm is disrupted by keeping long and irregular hours. Because of this, it is important to keep a regular sleep schedule and allow plenty of time for quality sleep, allowing these two vital biological components -- the sleep/wake restorative process and the circadian rhythm -- to help us perform at our best.

How can the circadian clock be reset?

For those individuals whose circadian clock becomes misaligned with their daily activities there are a couple of interventions that can be used to bring it back to an optimal cycle.

1. Bright light – use of bright light (either sun light or artificial light) can be used to set our circadian clock to a desired timing. Light in the morning advances the clock and light in the evening delays the clock.
2. Melatonin – taking melatonin before bed can advance the clock and melatonin after sleep can delay the clock.

Though light and melatonin are widely available, we encourage you not to set out on intentionally adjusting your circadian clock without first consulting a sleep specialist. There are aspects of response to these stimuli and side effects from them that must be considered on an individual basis prior to implementation.

HygieneTips for Successful Sleep

1. Establish a regular routine that includes going to bed and getting up at the same time every day, even on weekends. Maintaining a consistent sleep-wake cycle is the key to better health overall.
2. Get an adequate amount of sleep every night. Determine the amount of sleep you need by keeping track of how long you sleep without using an alarm clock for a week. Maintain this “personal” sleep requirement.
3. Go to bed when you are sleepy. If you have difficulty falling asleep or wake up shortly after going to sleep, leave the bedroom and read quietly or do some other relaxing activity. Avoid overly bright lights as this can cue your wake cycle.
4. Develop sleep rituals before going to bed. Do the same things in the same order before going to bed to cue your body to slow down and relax.
5. Avoid stress and worries at bedtime. Address tomorrow’s activities, concerns or distractions earlier in the day. Certain activities, such as listening to soft music, reading, or taking a warm bath can help you wind down.
6. Use your bed for sleeping and sex only. Often, doing other activities in bed like watching TV, paying bills, or working only serve to initiate worries and concerns. Let your mind associate bed with sleeping, relaxing and pleasure.
7. Avoid heavy meals late in the evening; similarly, avoid going to bed hungry. A light snack, especially dairy foods, can help you sleep.
8. Reduce your intake of caffeine and nicotine 4-6 hours before going to sleep. Stimulants interfere with your ability to fall asleep and progress into deep sleep.
9. Avoid alcohol 4-6 hours before bedtime. As a depressant that slows brain activity, alcohol may initially make you tired, but you will end up having fragmented sleep. In addition, being tired intensifies the effects of alcohol. Alcohol also aggravates snoring and sleep apnea.
10. Exercise regularly. Regular exercise, even for 20 minutes, 3 times a week, promotes deep sleep.
11. Don’t nap for more than 30 minutes or after 3 p.m. Avoiding naps all together will ensure that you are tired at night. Longer naps disrupt the body’s ability to stay asleep.
12. Maintain a dark, quiet, and cool room to sleep in.
13. Use sleeping aids conservatively, and avoid using them for more than one or two nights per month. Avoid sleeping pills altogether if you have obstructive sleep apnea; it can be a deadly combination.