The body clock: diving deeper

This article is part of a collection inside The Possums Sleep Program called Deeper Dive, which explores the complex scientific, historical and social contexts in which families and their babies or toddlers live and sleep. You don't need to read Deeper Dive articles to be helped by The Possums Sleep Program.

How does the body clock work?

You can find out about your baby's body clock here, and your toddler's body clock here. This page takes a deeper dive into the sleep science. If you're just starting out with The Possums Sleep Program, and you need help with your little one's sleep, I suggest you start here.

The body clock is one way in which the great powers of Nature and our planet's Sun interact with every cell in our body. Our fragile human bodies are part of the great natural cycles of our planet and solar system. As the Sun rises over the eastern horizon, then disappears behind the west, waves of neurohormones wash through our delicate blood vessels, signals tracking the Sun. These rhythmic molecular waves are co-ordinated by a cluster of neurons in our brain known as the circadian clock.

By working with your small child's body clock, you are helping the rise and fall of her vital energies stay connected with your own daily rhythms, and with the great natural rhythms of the world around her.

In the absence of light, our bodily neurohormonal systems still cycle through circadian rhythms, but they are crisply synchronised with the world around us by the Sun and it's effect upon our body clock.

Our circadian rhythm is the changes in body and behaviour which follow the 24-hour cycle of light and dark caused by the Earth spinning on its axis. When light falls on the cells at the back of the eye, signals travel directly to the body clock, causing alertness and wakefulness. Our body clock balances the signals which cause wakefulness with other brain signals which inhibit wakefulness and cause sleepiness.

Many different hormones and chemical factors rise and fall in response to the body clock's daily signals, affecting most cells in the body. For example, your breast milk contains changing levels of hormones including melatonin and cortisol, derived from your blood stream. These hormones can be used to track your body clock's response to light, though they are not driving your body clock.

What other biological processes are kept in sync with day and night by the body clock?

A myriad of signals interact together to create your or your little one's circadian rhythms. Noise and activity, which usually occur more during the day and less at night, affect the settings of our body clock, though only a little. Other environmental factors like food and temperature also have a small effect. The body clock's changes are before all else driven by the Sun.

In case you're interested, here are some other biological rhythms kept in sync by your body clock.

• Heart rate

• Blood pressure

• Kidney waste filtration (highest during day, less at night)

• Body temperature (with lowest body temperature just before dawn, about two hours before usual get-up time)

• Pancreatic secretions (which control blood glucose levels)

• Stress hormones (which help wake us up at the beginning of the day, for example). You can find out more about cortisol and your little one's sleep here.

• Melatonin secretion (which starts after dusk). You can find out more about melatonin and your little one's sleep here.

When I pause to reflect on the sleep science in this way, I remember yet again just how dependent each precious human body is, not just on the natural world around us, but on our solar system and the Sun, hour by hour, night after day, right down to the tiniest cell of who we are. Perhaps this is how the language of science comes to speak an imagining as old as the many different religions of the world - that ancient human story told across all cultures that we are somehow and quite mysteriously a part of (even, if you wished to imagine it this way, held and protected by) strangely vast and incomprehensible natural powers.

Selected references

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Borbély AA. A two process model of sleep regulation. Hum Neurobiol. 1982;1(3):195–204.

Jenni OG, Carskadon MA. Sleep behavior and sleep regulation from infancy through adolescence: normative aspects. Sleep Medicine Clinics. 2007;2(321-329).

Gallaher KGH, Slyepchenko A, Frey BN, Urstad K, Dorheim SK. The role of circadian rhythms in postpartum sleep and mood. Sleep Medicine Clinics. 2018;13(3):359-374.

Lillis TA, Hamilton NA, Pressman SD, Khou CS. The association of daytime maternal napping and exercise with nighttime sleep in first-time mothers between 3 and 6 months postpartum. Behav Sleep Med. 2016:doi:10.1080/15402002.15402016.11239580.

Morales-Munoz I, Partonen T, Saarenpaa-Heikkila O, Kylliainen A, Polkki P, Porkka-Heiskanen T, et al. The role of parental circadian preference in the onset of sleep difficulties in early childhood. Sleep Medicine. 2018;54:223-230.

Wong SD, Wright KP, Spencer RL. Development of the circadian system in early life: maternal and environmental factors. Journal of Physiological Anthropology. 2022;41(22):https://doi.org/10.1186/s40101-40022-00294-40100.

Yoshida M, Ikeda A, Adachi H. Contributions of light environment and co-sleeping to sleep consolidation into nighttime in early infants: a pilot study. Early Human Development. 2024;189:105923.