Circadian Rhythm: key factor #2 in regulating sleep

We each have an internal biological clock that regulates and sets the tempo for our physiological processes throughout the day. This includes sleep, digestion, & body temperature, amongst others.

What is the circadian rhythm? How does our internal clock work?

Our internal clock runs over a period of around 24 hours. For some it’s slightly longer and for others slightly shorter, depending on the genetics of the individual. As our clock is not precisely aligned with the Earth, it requires constant resetting (to 7am each day for example) to avoid us becoming gradually out of sync with our natural environment.

Our wake time is the anchor in our sleep-wake cycle, and daylight is the most powerful signal for resetting our internal clock. Morning light sends a signal to our brain which, just like a conductor, orchestrates the physiological symphony of our day. It tells our organs when to trigger the right hormones and when throughout the day. If everything is well orchestrated, i.e. if this circadian rhythm is regular, we are typically at our best physically and mentally.

Regularity is the pillar of our internal clock

Irregular sleep schedules, meal times, and exposure to light late in the day all weaken our circadian rhythm. Keeping a regular waking schedule is fundamental for optimal functioning, not only for sleep, but for all of our body’s physiological processes. The most important thing you can do to optimise your circadian rhythm is to wake up at the same time every day, including weekends.

At first, it may seem extremely difficult to maintain a consistent wake-up time, especially when we experience sleeplessness at night. We may feel very tired for the first few days, but this only lasts for a short time. Gradually, our body becomes acclimatised to this new rhythm. After a few days or weeks we will be automatically ready to start the day naturally, at the desired time. This also sets our natural sleep time in the evening. Remember: we cannot force ourselves to sleep at night but we can force ourselves to get up at a specific time each day. This becomes our sleep anchor.

Perseverance is key. It is better to endure a few bad nights of sleep than to experience poor sleep for months or years.

Getting up at the same time also helps us to build up sleep pressure, as we no longer stay in bed in the morning to compensate for a bad night. As a result, our sleep pressure remains constant or even increases, which ultimately promotes sleep.

Social jet lag

“Social jet lag” is a phenomenon that refers to how we shift time zones, often for social reasons, and without even travelling. For example, if during the week, we go to bed at 11pm and get up at 7am, but at the weekend we go to bed at 1 or 2am and then get up at 10 or 11am our internal clock becomes confused: it’s as if we are living in Paris during the week and in Dubai at the weekend. We are completely out of sync. It’s not surprising that we find it harder to fall asleep on Sunday night, and waking up and getting up on Monday is also difficult. Sleep pressure is at an all time low on Sunday, and the circadian rhythm is out of whack on Monday morning when we have to get up for work or other obligations. When we suffer from insomnia, it is not necessarily because social reasons that we shift, but we tend to compensate in the same way because we are desperate to sleep whenever we are able to do so. By doing this we are doing ourselves a disservice. Maintaining the same schedule during the week and at the weekend is key.

Alternating light and darkness: the other pillar of the circadian rhythm

The alternation of day and night, the exposure to light and darkness, plays a crucial role in the regulation of sleep. This also has an impact on melatonin, the natural hormone that triggers sleep. In the evening, melatonin is gradually secreted. It is released by darkness and is suppressed by light. Light, as we saw earlier, signals to the brain that it is time to wake up.

Exposure to light at night disturbs your sleep. Today, bright light sources are everywhere and severely impact our internal clock. When we are exposed to light at night, our brain receives a signal that it is not yet time to go to sleep.

The blue light emanating from our mobile phones, computers, tablets and other devices, actively suppresses melatonin, the sleep hormone. Whenever possible, follow the lead of the sun and adopt the habit of dimming the lights in your home at sunset. Use lamps instead of ceiling lights, put blue light filters on your devices and if you get up during the night try to use dim lights.

Avoid using electronic devices for at least an hour before bedtime, not only because of the blue light but also because these devices are associated with daytime stimulation and the secretion of dopamine, an excitatory hormone that prevents sleep. Anything that relaxes you before bed contributes to a good night’s sleep.

Conversely, you are able to reinforce your circadian rhythm by exposing yourself to daylight as early as possible each morning. If there is little light where you live, you can invest in a light therapy lamp. They are inexpensive and very effective, especially in winter for those who suffer from Seasonal Affective Disorder (SAD). If you opt for a light therapy lamp, make sure it has a minimum output of 10,000 lux and stay close to it for 30-60 minutes when you wake up.

Other synchronisers

Because our programming is relatively accurate, but not exact, we need nudges throughout the day to keep our internal clock properly aligned. These small corrections, the rewinding of the clock, are called zeitgebers (literally time givers in German). They are “little nudges” that move our internal clock in one direction or another, to help it to stay on time. The main zeitgebers, or synchronisers, in addition to light are:

• physical exercise,
• meal times,
• working hours,
• temperature,
• socialising activities such as meeting friends or working.

All of these factors allow us to ‘tune in’ to our environment.

In summary, what do you need to do to strengthen your circadian rhythm?

• Get up at the same time every day (including weekends), even if you didn’t get enough sleep during the night
• Expose yourself to daylight/ light therapy lamp as soon as you get up
• Reduce your exposure to light at night by diming your lights
• Whenever possible maintain the same schedule for your meals, sports, social and work activities

What factors weaken the circadian rhythm?

• Irregular sleep patterns
• Irregular meal times
• Light exposure in the evening / not enough light exposure during the day, especially in the morning