Do you know the feeling when you can’t find sleep even when you have the chance to rest? This can be extremely frustrating but is very common when the two key systems that play a major role in producing sleep get out of balance: the sleep drive mechanism, or sleep drive pressure and the wake drive mechanism, your circadian clock.
Both factors are powerfully influencing your mind and body and their interaction either keeps you awake or triggers the onset of sleep. Any disruption in either system takes the whole sleep process off-balance and can cause chronic health conditions, such as obesity, diabetes, seasonal affective disorder, depression and of course insomnia.
What are the circadian rhythm and the sleep drive mechanism?
Your circadian rhythm is created by your internal 24-hour clock located in the middle of your brain. This clock creates a day-night rhythm that either makes you feel alert or tired, depending on the time of the day.
Your sleep drive mechanism is a chemical substance that builds up in your brain. The longer you’ve been awake, the higher the concentration of this chemical and the stronger your sleep pressure. In other words, the more tired you feel.
How does your circadian rhythm affect your body functions?
Cycling within 24 hours, your circadian rhythm (“circa” meaning around and “dian” meaning day) determines when you want to be awake and when you want to be asleep. The key point is that this clock, located deep in the brain, causes the opposite of sleepiness by opposing the action of the sleep drive mechanism. The wake drive of the clock gets stronger during daylight hours, but weaker during the night.
But your circadian rhythm does much more than “just” coordinating your sleep-wake cycle! You can think of it as a master system affecting all the mechanisms of your brain and body. It controls your eating habits and digestion, your core body temperature, your urine production, your metabolic rate, and activates many other vital bodily functions. Besides, your circadian rhythm influences the release of various hormones and strongly impacts your moods and emotions.
What is the relationship between your circadian rhythms and your sleep?
There is one hormone which is essential for you to become drowsy: melatonin. The sleep hormone melatonin is made by your pineal gland, but it’s your biological clock which controls its production. And the main influencing factor in the production process is daylight – or merely the lack of it. The less sunlight there is, the more melatonin is produced. That is why melatonin is also called the “vampire hormone”.
Here is how the production process of melatonin works: Through your optic nerves, your internal clock receives information about the intensity of incoming light. When it’s getting dark at night, your internal clock communicates to the brain to release more melatonin with the consequence that you get sleepy.
Once you’re sleeping, the melatonin level slowly decreases during the night. As the daylight in the morning enters your brain through your optical nerves, your pineal gland stops the production of melatonin, whereas your cortisol levels are now high. This is the signal to your brain and body to change state into conscious and active wakefulness. Then, at night, when darkness falls, your melatonin level rises again and calls for another sleep event.
That is why changing the light-dark cycles can strongly influence your biological clock and your circadian rhythms and alter sleep-wake cycles. Examples for those influencing factors are shift work or the exposure to light from computer screens and mobile devices during the night.
The resetting quality of daylight
One interesting factor of your circadian rhythm is that it is not exactly 24 hours in length but around (“circa”) one day (“dian”). Normally, this timing mismatch would leave you feeling tired during the day and active at night after a while – if there wouldn’t be a regulator that keeps you on schedule.
And this is where natural light comes into play. Every morning when you wake up the light of the sun resets your biological clock. This way, your natural day/wake-night/sleep cycle stays in sync and can repeat over and over without fail. In short, nightfall is a trigger for you to sleep, and daybreak is a trigger for you to wake up.
Do you know your chronotype?
Although we all have a circadian rhythm that steadily marches up and down every single day, the respective peak and low points are not the same in everyone. Each person has an individual preference, when they prefer to sleep or when they are most alert, also known as their chronotype. Knowing your chronotype can help you boost your health, happiness, and productivity. It also helps you to understand if you really have insomnia.
So-called “morning larks” have their peak of wakefulness early in the day, and that’s when they often function best. They feel sleepy early at night and go to bed at a time when some “night owls” are just starting to become active.
Most night owls cannot fall asleep early at night, no matter how hard they try. Some of them may only be able to drift off in the early-morning hours. As a consequence, night owls usually hate to wake up early. If they have to, they often struggle to function well at this time because their brain is still in an offline state.
Morning larks and night owls are the extremes. Around one-third of us lies somewhere in between. And it may also change over time. When I was younger, I used to be a morning lark. But now in my forties, I am more of an “in-between the two types” of person, still with a slight leaning towards morningness.
Important to notice is that you can’t choose to be a night owl or a morning lark. Your chronotype is determined by genetics. If you are more of a night type, ‘it’s likely that one (or both) of your parents is one too.
What triggers your sleep?
Your twenty-four-hour circadian rhythm is the first of the two factors determining wake and sleep. Let’s now look at the second factor: sleep pressure or sleep drive mechanism which is facilitating sleepiness.
During the hours that you are awake, the pressure to sleep increases steadily – your sleep drive goes up. Usually, your body will provide you with cues that it is important to go to sleep. Then, as you sleep, the need for sleep diminishes – your sleep drive goes down. In other words, your sleep drive mechanism is a time tracking system for the amount of time you are awake and the amount of time you are asleep.
What happens in your body when creating sleep pressure?
With every minute you are awake, a chemical substance called adenosine builds up in your brain, which creates sleep pressure. That means the longer you are awake, the more adenosine will accumulate, and the sleepier you feel. When the concentration of adenosine peaks, you feel an irresistible urge for sleep. Usually, this happens after 14 to 17 hours of being awake. A normal sleeper has then created enough drive to achieve 7 to 8 hours of sleep at night.
Think of it as an ocean wave growing in size and strength. Then as it hits the shore, it breaks and flattens out. Your sleep drive acts in the same way as is it growing through the day and peeking at night when you go to sleep. Then it disappears until morning just to start rising all over again.
Your sleep drive and wake drive is a delicate interaction
Synchronization between your sleep drive and your wake drive produced by your internal circadian clock is crucial to regulate sleep and wakefulness. If both systems are in balance, they interact as shown in this figure.
During the day, you stay awake because your wake drive is increasing and remains stronger than the sleep drive. However, your sleepiness also increases during the day so that it becomes stronger at night than your wake drive from the circadian clock. This revers mechanism keeps you asleep. Then in the morning, the relative strengths reverse again. You wake up and stay awake until the next evening.
What happens when your sleep/wake drives get off-balance?
As you can see your sleep and wake drive is a complex interplay. Any disruption in this system may negatively impact both your wakefulness during the day and sleep at night. There are many possible disturbing factors. They can be of biological or environmental nature and have in common that they either increase your perception of insomnia or truly contribute to insomnia.
Here is an overview of the most common mechanisms that influence your sleep/wake drive:
Extensive napping during the day
If you nap too long or too often during the day, the strength of your sleep drive at night is likely reduced. As a consequence, you may not get sufficient restful sleep during the night to reduce your sleep drive (adenosine levels remain too high) which leaves you with an undesired greater level of sleep drive in the morning.
So no napping? A brief nap of twenty or thirty minutes during the day normally doesn’t affect your sleep drive and is okay, even if you have problems to sleep at night. I even would recommend it as it helps to reset your brain and boosts physical energy, mental alertness, and your mood. Also, napping after lunch is a natural thing to do because that’s when your circadian clock switches from high-degree wakefulness to low-level alertness.
Irregular sleep schedules
Continually changing your sleep time is one of the main reasons for poor sleep. For example, sleeping for too long in the morning or too early in the evening (e.g., while watching TV or Netflix…) will all reduce your nighttime drive to sleep.
That may also be the reason why you have problems falling asleep on Sunday nights. As you had a late night on Saturday, you got up late on Sunday morning to catch up some sleep. The long sleep may feel great, but the problem is that the timing of your internal clock has been delayed to a later time too. Consequently, you have an insufficient drive for the next night, and so the process is repeated.
As a result, you aren’t able to fall asleep on Sunday night which frustrates you. This feeling, in turn, activates your stress response system waking you up even more. If continued, it can end up in a vicious insomnia cycle of insufficient sleep drive at night and lack of wake drive in the morning.
Remember, your body clock is a creature of habit. Staying in bed longer than your average rise time resets your internal clock to a new time and upsets the cycle for the night. Therefore, a regular sleep schedule is the #1 advice to everybody struggling with sleep.
As you are aging
Everyone is different, but as a teenager, maybe you too have found it easier to stay up until late at night. Then in the morning, you were struggling to get up. As you got older, this might have swung in the other direction. You are getting sleepier earlier in the evening and tend to wake up earlier in the morning than you did before.
The reason for this shift in the sleep period relative to the day/night cycle is not necessarily a desire to stay up late or to go to bed early. It is merely biological.
Also, from middle age on, the interaction between your sleep drive and your wake drive flattens a bit. As a result, you may not sleep as well as you used to, and you may be less alert during the day. If this sounds familiar to you, keep in mind that these changes are natural with age and not necessarily a sign that something has gone wrong with your sleep.
When you travel through different time zones, your biological clock differs from the local time. For example, if you fly from California to New York, you “lose” 3 hours. If you wake up at 7:00 am on the east coast, your biological clock is still running in west coast mode, so it fees like 4:00 am.
Eventually, your internal clock will adjust, but this often takes a few days (around one day for each readjusted hour). As a result, you feel tired and sleepy during the first days in a different time zone because your biological clock still thinks it is nighttime.
One thing you can do to better adjust to a new schedule is getting natural light on to your skin in the morning. Remember, light acts to reset your biological clock. Going for a quick walk outside helps your internal clock to keep on time and improves the quality of your sleep the following night. If going outside is not an option you may find using light therapy boxes which mimic the sunlight helpful.
Maybe you have never experienced any sleep problems before, but suddenly your circumstances change, and you have to sleep in a noisy environment. Then things can literally change overnight. Sound from a TV, people talking, traffic noise, a snoring bed partner, or neighbors having a party – all these are examples of environmental factors that affect your natural biological mechanisms for sleep.
There are several ways how to deal with unwanted noise. I have written a long blog post about the impact of noise on our sleep and possible solutions on how to avoid it which you can find here.
For most people with poor sleep (me included), the biggest challenge is to quieten their overactive mind. Sound familiar? While lying awake in bed, you ruminate about the past, dwell on current problems, or worry about the future. The problem with those racing thoughts is that they can completely take over your mind, leaving you unable to focus on anything else. As a result, you are feeling insecure and anxious, your stress response system ramps up, and sleep is pushed further away.
Although an overactive mind can be so debilitating, there is a lot you can do to quieten your mind and to create more balanced thinking. As overthinking was the primary cause for my sleeplessness, you may find my article How to Calm Your Racing Mind at Night helpful. Here you can learn some simple techniques which you can use right away to reduce racing thoughts.
Then there are, of course, also numerous physical conditions that can cause sleep disturbances. The most common one is pain, but it could also be allergies, indigestion, tinnitus, cramps, fever, or side effects of drugs. It’s again a vicious cycle in which pain worsens your sleep patterns, and poor sleep worsens the pain. Often but not always a successful insomnia cure also alleviates the pain.
If you are suffering from both chronic pain and insomnia, CBT (Cognitive Behavioral Therapy) or ACT (Acceptance and Commitment Therapy) – or a combination of both – is often an effective way to approach your condition. These therapies help you to better cope with your pain and sleep problems by changing the way you think and behave.
Your biological clock and circadian rhythms are produced by natural factors within your body, but they are also strongly affected by your environment. There is variability in how well our body clocks can handle environmental changes. Some people easily adjust to external changes, such as travel across time zones or Daylight Savings Time, or they feel okay with an irregular sleep schedule. However, most of us have difficulties adjusting to those changes, and we may experience sleep problems.
I hope that this overview of how your sleep/wake mechanism works was helpful to you. Remember, a regular circadian rhythm and sleep/wake drive are vital for your health. If your internal clock runs too slow or too fast, it can cause chronic insomnia or other serious health problems. There is a lot you can do to balance your sleep/wake drive mechanisms. First, make sleep a priority in your life and second, keep a regular sleep schedule – and you’re off for a good start!