What Is Your Circadian Cycle?

There are very few things in nature that are linear, everything moves in circles of changing and adapting life patterns. As humans we have natural body and brain cycles that run over a 24 hour period.

These cycles or rhythms control many body functions switching them on or off at the most appropriate times. For example the circadian rhythms are responsible for or have an influence over:

• Feeling hungry
• Body temperature
• Sleep-wake-sleep patterns
• Hormone production
• Cell regeneration

These rhythms are found not just in humans but in other animals, plants,fungi and even some bacteria. Scientists have found that these rhythms are *endogenously generated, but there are environmental factors that also have an influence - such as how much day light there is and seasonal temperatures.

*Endogenously means that the body produces these rhythms from within.

Biological Clocks.

Within the cells of our body, there are certain molecules that are responsible for driving the circadian cycles. They are in turn controlled by one master biological clock that is found in the brain. The hypothalamus has an area within it called the SCN (suprachiasmatic nucleus). There are about 20,000 nerve cells within the SCN and lying just above our optic nerve in the eye. This proximity to the the nerve of vision is able to relate immediate information on how light or dark the environment is. In addition, our personal circadian rhythms are determined genetically by how our mother and father's cycles operate.

One of the main functions of the circadian cycle is to regulate our sleep-awake-sleep patterns. So much so that any interruption of the rhythm can have unpleasant side effects - this is why we experience jet lag. However, many people also suffer from sleep disorders that are thought to be wholly or partially influenced by factors affecting the circadian cycle.

Circadian cycle and sleep

The body's master biological clock that we mentioned earlier - SCN (suprachiasmic nucleus) controls the release of a substance called melatonin. Melatonin is a hormone secreted by the pineal gland in the brain - and it's this hormone that makes you feel sleepy at night time. Medical researchers have found that as we get older, less melatonin is released. This is probably one reason young people usually don't have any problems sleeping as they will have higher amounts of melatonin secreted.

Babies don't have a functional circadian cycle until about 12-16 weeks - this is why they can seem to turn night into day. New born babies for example don't develop their light-dark cycles until about 6 weeks old. However, even at 12-16 weeks, babies are still developing their rhythms - they will only slowly mature into longer sleeping patterns at night.

Jet lag

In the case of jet leg what happens here is that although you travel through different time zones, your circadian cycle is set to your home environment. Your watch might say 9am, but your circadian rhythms are still in a home cycle where it might be 9pm. Eventually your circadian rhythms will come back into tune but it can take a few days. How severe you experience jet lag normally depends on how many time zones you cross and the distance travelled. The main symptoms are:

• Sleep disturbance - this is one of the most common problems and in severe cases people can find themselves wide awake at night while feeling very tired during the day.
• Confusion
• Headaches
• Lack of concentration, poor memory.
• Gastric upsets - diarrhoea, nausea, loss of appetite etc.
• Anxiety
• Disorientation, feeling light-headed
• Irregular periods can occur in women who travel frequently.
• Movements are clumsy, un-coordinated.
• General ill feeling, muscle pain and sweating.

However the circadian cycle can cause more than jet lag. Sleep disorders as well as obesity and diabetes have all been linked to problems with these body rhythms.

To finish off we'll have a brief look at what happens when the circadian cycle goes wrong - and possibly leading to problems such as sleep disorders.

One of the most common sleep disorders is Circadian Rhythm Insomnia. This is where the person's natural rhythm of 'dark-sleep, light-awake' is disrupted for some reason. The most common causes for this disruption are:

• Jet lag - usually this will correct itself unless you are someone who constantly travels through different time zones.
• Shift work - people who rotate shifts can have sleep problems and also those who work constant/frequent night shifts.
• Advanced or delayed sleep phase syndrome - these conditions involve people becoming tired and then alert at inappropriate hours of the day and night.
• Non 24-hour sleep/wake disorder - this involves periods of insomnia that tend to occur at different times each night. People may wake up late in the morning for example and fall asleep later at night. They will also experience periods of falling asleep perhaps in the evening and waking up in the early hours of the morning.

The treatment for circadian sleep disorders depends on the particular sleep problem affecting the person. Once this is established a number of therapies can be used to try and get the person back into normal rhythms. For example some treatments might involve:

• Cognitive therapy
• Relaxation
• Self-hypnosis
• Bright light therapy
• Chronotherapy - this is where bedtime is slowly adjusted until the desired time for sleeping and waking is reached.

For many people a combination of techniques is often required rather than just one.

Lastly, if you do have problems with your sleep patterns, then speak to your doctor. Disturbed sleep doesn't just result in loss of a few hours rest that you can make up at some other time. Without regular, refreshing sleep, people can develop numerous physical and mental health conditions.