The word circadian has its origins in Latin. It’s derived from ‘circa diem’, which means around the day.1
So, the phrase ‘circadian rhythms’ refers to 24 hour cycles that are part of our internal body clock. We actually have more than one circadian rhythm, but perhaps the best well known is the sleep-wake cycle. Other rhythms regulate hormonal activity, body temperature throughout the day and night, and eating and digestive processes.3
From a sleep perspective, the circadian rhythm is designed to make sure we sleep at night and remain wide awake during the day. However, there are things that can interfere with that cycle such as shift work and jet lag.2 More about that later.
How does it work?
During the day, light exposure suppresses a natural hormone called melatonin, which is produced in the brain. Melatonin hormone simply tells your brain it’s time for sleep. Conversely, exposure to darkness tells the brain to start producing melatonin. 3,4
(If you want to learn more about melatonin, read this article.)
The circadian clock starts to prepare your body for sleep (with melatonin) about 2 hours before your usual bedtime and maintains that status throughout the night, until about 1 hour after usual wake-up in the morning.5
Exposure to light around these sensitive times can affect your sleep patterns.5
For example, bright light in the evening two hours before usual bedtime will shift the time for sleep later, and you may wake up later in the morning. On the other hand, bright morning light will tend to shift the time for sleep earlier, so you’ll begin to fall asleep earlier in the evening and wake up earlier in the morning.5
When our circadian rhythm is disrupted, so is our sleep, leading to insomnia and daytime sleepiness, neither of which are desirable.
The two most common ‘disrupters’ are probably jet lag and shift work.2 Shift workers need to employ specific sleep strategies to cope with the impact on their circadian clock. So, darkness during the day becomes very important. Jet lag is simply the result of changing international time zones. Your body thinks it’s in the same place you were 24 hours ago and begins the preparation for sleep, before it slowly adjusts to the new zone. One of the best ways to combat jet lag is to expose yourself to sunlight in the new location, to shut down production of melatonin.2
But what about the rest of us? Can we harness the power of our circadian rhythm to help improve our sleep patterns?
The short answer is yes.
Sleep hygiene is a topic in its own right, so we won’t go into that right now, but you can find some useful tips here:
In the meantime, as you’ve probably now gathered, light is the ‘enemy’ of sleep. Whether it’s daylight, artificial room lighting or the blue light of screens, even the smallest exposure can stimulate wakefulness. In fact, a study investigating the impact of just 5 minutes of light exposure through the evening, (for example, a bathroom visit from your partner), triggered a delay melatonin release by a staggering 2.3 hours, leading to the inability to sleep through the night, and greater morning fatigue.6
So, stay away from devices before bed and if you have problems making your bedroom dark enough, invest in a good quality sleeping mask and help your natural melatonin work its magic. Check out the comfortable and affordable Dreamlight Masks here.
- Olivia Arezzolo blog/Body and Soul article