In brief
The physical, mental and behavioural changes your body goes through over a 24-hour cycle. A master clock in the brain keeps them in time, guided mainly by light.
- Cortisol levels follow a daily pattern, rising in the early morning.
- Jet lag and shift work alter the normal sleep-wake cycle.
- Long-term sleep loss and continually shifting circadian rhythms can increase the risks of obesity, diabetes, mood disorders, heart and blood pressure problems, and cancer.
How it works
The master clock is a structure in the brain called the suprachiasmatic nucleus (SCN). It controls the production of melatonin based on how much light the eyes receive, and it keeps the rhythms of other organs and tissues in step, since nearly every tissue has its own rhythm.
Circadian rhythms affect sleep patterns, hormone release, appetite, digestion and body temperature. Light has perhaps the greatest influence. In the evening the master clock tells the brain to make more melatonin, causing sleepiness, and light at night can lower the amount of melatonin you make.
Connections
5 connections on the map. Select a topic to read its page.
Body clock (circadian rhythm) helps control
Your body clock helps control when you feel sleepy and when you are typically awake.
Sources: healthdirect Australia, Sleep; National Institute of General Medical Sciences (NIH), Circadian rhythms
In the evening, the master clock tells the brain to make more melatonin, causing sleepiness.
Sources: National Institute of General Medical Sciences (NIH), Circadian rhythms; healthdirect Australia, Melatonin
Cortisol levels follow a daily pattern, rising in the early morning.
Body clock (circadian rhythm) is controlled by
Light has perhaps the greatest influence on the body clock, which controls melatonin based on how much light the eyes receive.
Sources: National Institute of Neurological Disorders and Stroke (NIH), Brain basics: understanding sleep; National Institute of General Medical Sciences (NIH), Circadian rhythms
Body clock (circadian rhythm) is supported by
Keeping regular sleep patterns, going to bed and waking up at around the same time every day, helps sleep, according to healthdirect.
Sources: healthdirect Australia, Insomnia; healthdirect Australia, Sleep
Sources
Each connection above names its own source. See every source AskBioMap uses.
Summarised from the NIH, healthdirect and Pathology Tests Explained. Sources read on 13 and 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.