What is the circadian rhythm?

How do biological rhythms work?

Circadian rhythms are one of four of the body's biological rhythms, all of which play an important role in our bodies’ daily functions. All of the biological rhythms are made up of thousands of nerve cells in the brain that sync up our body’s activities and day to day functions.

The other three biological rhythms are:

• Diurnal Rhythms which is a biological rhythm that is synced with day and night.
• Ultradian Rhythms which are biological rhythms that last fewer than 24 hours. An example of an ultradian rhythm is the sleep cycle between REM (Rapid Eye Movement) and non-REM sleep, which is a repeated cycle that happens when we sleep.
• Infradian Rhythms which is a biological rhythm that lasts longer than 24 hours. Examples of this includes the menstrual cycle.

What do Circadian Rhythms have an effect on?

Circadian Rhythms influence our bodies a lot. These include body temperature, sleep and wakefulness, and hormonal changes. The circadian rhythms are controlled by the brain and there are various factors that can affect our circadian clocks. This can include exercise, hormones, and medication.

One of the biggest things that can affect our circadian rhythm is our bodies’ reception of light and darkness. When you understand its effects on your body, you can use light and darkness to your advantage to stay awake and alert during the day and rest better at night. Our internal circadian clock is most sensitive to light two hours before bedtime and about one hour after you wake up. This is why people can suffer from Seasonal Affective Disorder, as there is sometimes a change in the circadian rhythms when the seasons change and there is less daylight in winter.

How does your circadian rhythm get out of sync?

Sometimes it's not possible for us to follow our circadian rhythm, as our lifestyle choices and needs can clash with our body clock. These include:

• Overnight/shift work: People who regularly work various shifts patterns or night shifts can lead to circadian misalignment. This can lead to various issues that can affect physical and mental health including people's ability to exercise, socialise, and eat balanced meals.

• Jet Lag: When we go on holiday (or when we return home from holiday), we sometimes find ourselves waking up super early or falling asleep really late because our body’s sleep-wake cycle is out of sync to our new location as we cross multiple time zones.

• Stress: Several studies have shown that stress can have an effect on our circadian rhythms. For many of us though, stress is unavoidable. It is important to find ways to manage stressful situations, so you can still achieve a good night's sleep. Studies show that stress can be seen as an additional demand on our psychological and physiological capabilities and can affect individuals' sleeping patterns because the hormonal and neuronal pathways and the circadian regulations in the brain are closely related.

• Health conditions: Both mental and physical health conditions can affect our circadian rhythms. Mental health conditions, like depression, can lead to altered circadian rhythms and sleep disturbances, which is why seeking proper medical treatment is always important for any physical or mental health condition.

Circadian Rhythm Disorders

Delayed Sleep Phase Disorder (DSP)

People who suffer from DSP are not able to fall asleep at a normal time, and then struggle to wake up at their desired hour in the morning. People who have this condition can normally find it difficult to:

• Fall asleep - they normally fall asleep after midnight because their body is staying alert until late into the night.
• Wake up - because their internal systems aren’t producing enough signals to alert their body that it's time to wake up.

This is most seen during adolescence. People who suffer from DSP are likely to miss class or have poor performance. For people with DSP, they don’t choose to stay up late, they can’t fall asleep earlier even if they tried to.

If you struggle to change your sleeping patterns, speaking to a sleep specialist can help you find suitable treatment. Normally, bright light therapy helps with this disorder. Light is used to gradually shift your sleeping pattern to a more convenient schedule.

Advanced Sleep Phase Disorder (ASP)

ASP is more common in older adults, where they get tired in the early afternoon and in turn end up falling asleep really early or find themselves waking up really early in the morning and unable to get back to sleep. This is not easy to diagnose in comparison to DSP because people with ASPD are still able to attend work, school and social activities during the day.

Irregular Sleep-Wake Rhythm

People with Irregular Sleep-Wake Rhythm cannot stick to a regular sleep pattern because of some form of absence of a circadian pattern in their sleep-wake rhythm. This is most commonly seen with people who have neurodegenerative diseases, like Alzheimer’s, and with traumatic brain injuries.

Some common symptoms are similar to insomnia, which includes difficulty falling or staying asleep and excessive daytime sleepiness. Treatments for this disorder vary, but all aim to strengthen circadian synchronising agents, like daytime exposure to bright light and structured physical and social activity routines.