Essential Sleep Mechanisms

The Circadian Rhythm Regulated By Our Biological Clock

Two main factors have an impact on our alertness during the day and when we feel tired at night. These are our circadian rhythm and a chemical substance called adenosine or sleep pressure. Every person has a twenty-four-hour internal clock located deep within their brain which regulates their circadian rhythm. This biological clock is rooted in our DNA and is called the suprachiasmatic nucleus (SCN) located in the hypothalamus. The SCN is the master clock which signals our body when it is time for sleep or wakefulness. It regulates dozens of other functions in our body such as core body temperature, blood pressure, hormonal flow, energy, metabolism, cognition, sociability etc.

Adenosine

What is Adenosine?

Adenosine is a chemical substance which builds up in our brain and creates sleep pressure. The longer we’ve been awake the more adenosine builds up and the sleepier we feel. High concentrations of adenosine turns down the volume of wake promoting regions in the brain. At the same time, sleep-inducing regions in the brain are turned up. Adenosine levels reach a peak after twelve to sixteen hours of being awake leading to an irresistible urge to sleep.

The Effects of Caffeine to the Body and the Connection With the Adenosine Sleep Signal

Certain chemicals can mute the sleep signal of adenosine. The most common one and widely used all over the world is caffeine. Caffeine is a psychoactive stimulant which blocks and effectively inactivates the adenosine receptors in the brain. Consequently, the sleepiness signal provided by adenosine to the brain is blocked. Despite the high levels of adenosine which would otherwise seduce you into sleep, caffeine tricks you into feeling alert and awake. Caffeine can have a bad impact on our quality of sleep and can cause insomnia. More information on that topic can be found on the page focused on the External Causes of Insomnia.

Melatonin & Cortisol

What is the Function of Melatonin (the Sleepiness Signal)

Melatonin is a hormone released by the pineal gland. It functions as a circulating messenger and signals to our brain and body when it is night or day. Melatonin’s nickname is the “hormone of darkness”. This is because it is mostly being released in the bloodstream in the period from sunset until nighttime. At night, melatonin signals darkness throughout the body and brain, thus regulating the timing when sleep occurs.

Once we are asleep the concentration of melatonin slowly decreases across the night and into the morning hours. At dawn, sunlight signals the brain to stop producing melatonin. The lack of melatonin in the brain signals the body to switch towards active wakefulness for the rest of the day.

What is the Function of Cortisol (the Wakefulness Signal)

Sunlight in the morning triggers the release of cortisol (and adrenaline) by our adrenal glands sitting right above our kidneys. This wakefulness hormone signals our entire body it’s time to wake up and start moving around. This is done by increasing our heart rate and tensing our muscles. Additionally, the release of cortisol in the morning sets a timer in our body for the release of melatonin in the evening around 12 to 14 hours later by the pineal gland. In other words, the wakefulness signal cortisol in the morning triggers the onset for the sleepiness signal melatonin at night.

Melatonin & Jet Lag

When is it Beneficial to Try Melatonin Supplementation?

Some people take melatonin supplements to facilitate the onset of sleep at night. Contrary to popular belief however, melatonin supplements have only a minor impact on the generation of sleep itself. For this reason melatonin is not considered a powerful sleeping aid for people suffering from insomnia. More information on this topic can be found on the Supplementation page as part of the category focused on the Treatments of insomnia. However, melatonin supplementation can be effective for people who are suffering from jet lag.

What is Jet Lag and When Does it Occur?

Jet lag occurs when travelling to other parts of the world which causes our twenty-four-hour clock unable to adjust to the local time zone. As a result, we feel tired and sleepy during the day in a distant time zone because our internal clock still thinks it’s nighttime. Vice versa, at nighttime we experience difficulties falling asleep because our biological rhythm believes it is daytime.

Acclimatization to a New Time Zone

Our body will naturally acclimate to a new time zone by way of sunlight signals in the new geographic location. However, this is a very slow process, taking around one day for each hour of time difference between the new location and the home time. For example, if you travel from San Francisco to London there is a time difference of eight hours. Consequently, it will take your body eight days to fully adjust to the new time zone.

Why Travelling East is More Difficult For Your Body to Get Used To

It is much harder to acclimate to a new time zone when traveling eastward compared to westward. The reason for this is because it will require us to fall asleep earlier than we would normally. This is generally harder to do than staying up for longer. An additional reason is because studies have shown that the average natural circadian rhythm in humans is twenty-four hours and fifteen minutes. This makes it somewhat easier to artificially stretch a day compared to shrinking it. This is where melatonin supplementation can be beneficial.

If a person would arrive at a distant eastward destination where it is nighttime, he or she may find it very difficult to both fall asleep and stay asleep. This is because his/her circadian rhythm still believes it to be daytime. In this situation taking a melatonin supplement will trigger an artificial rise in circulating melatonin in our system. Consequently, this chemically induced trick will signal our brain that it’s time to go to sleep and therefore increase the likelihood of actually falling asleep. More information on how to manage and minimize the negative effects of jet lag can be found on the page focused on How To Prevent and Reduce Jet Lag.