You might have noticed that you feel energized or sleepy at the same times every day. You circadian rhythm is the reason why. In the sleep context, the circadian rhythm is your internal clock which controls when you are alert and tired. Circadian rhythms have been observed in plants and animals as well.
A biological rhythm must meet some criteria to be considered circadian. It has to be endogenous (self-sustained), and last approximately 24 hours, even in constant conditions. It can also be reset by external cues. A good example is when you travel to a different time zone.
Adults usually have their lowest energy levels in the middle of the night. The exact time can vary depending on your sleep chronotype. Night owls have peak energy at different times compared to morning persons. The existence of an internal clock is more evident for shift workers and when you experience jet lag. Even the biannual hour shift can disrupt our cycle.
Besides the natural variations for each person, our sleep cycle and sleep needs also change during the course of life:
- Newborn babies: They still don’t have a well formed circadian cycle, that’s the reason why they sleep on and off. As their sleep cycle gets more consolidated, daytime naps are less frequent and sleep is consolidated during the night.
- Children: Children need more sleep than adults, 11-13 hours per night between age 3-5 and 10-11 hours between 6 and 9 years old.
- Teenagers: Hormonal shifts change the circadian rhythm, making them go to bed later at night, and waking them up later in the morning.
- Adults: Adults needs between 7-9 hours of sleep every night. Some lifestyle choices, such as consumption of caffeine, stress and screen use during the evening disrupt our sleep cycle.
Humans are diurnal animals, we live during the day and sleep at night. This is reflected in our circadian rhythm. Our sleep is heavily defined by the release of melatonin, also known as sleep hormone. This hormone is released during the evening, reaching its peak level at the middle of night, and decreasing to very low levels at the moment to wake up.
Light exposure is the most widely-known factor impacting our circadian rhythm but several others exist, such as temperature.
The disruption of this mechanism is linked to a number of disorders, such as bipolar disorder and delayed sleep phase disorder. It also believed to have long-term adverse effects on peripheral organs, especially the development of cardiovascular diseases.
Obesity and diabetes are associated with both genetic and lifestyle factors. Amongst them, disruptions in the sleep cycle might play a role in the development of metabolic disorders. Irregular eating times is associated with insulin sensitivity and higher body mass, which may lead to cardiovascular and hypertension in the long-term, reducing the life expectancy.
We also have some tips to help you regulate and maintain an healthy circadian cycle:
- Maintain a sleep schedule, even during the weekends
- Avoid blue lighting (screens) at night. They disturb your sleep cycle.
- Respect your chronotype as much as your lifestyle allows you