What is our body clock and why is it so important for your little one's sleep?

Our body clock is a cluster of nerve cells deeply buried on the undersurface of the brain. The body clock drives our circadian system, which controls the many cyclic changes occuring in human bodies over a 24-hour period. These include the cycles of sleep and wakefulness.

Humans can’t make sleep happen. Sleep isn’t under conscious control. This is why we can't teach your toddler to sleep. It’s also why you can’t train your toddler to sleep better (though you might hear people saying you can)! It's why sleep isn't controlled by sleep associations.

Whether we're adults or children, sleep is controlled by just two biological regulators, the body clock and sleep pressure.

What are the main things to know about the body clock so that your toddler's sleep is as easy as possible?

To have healthy sleep patterns, your small child's body clock needs to synchronise with your own. Your and your toddler's body clocks also need to synchronise with day and night. Your toddler's body clock is set by experiences of

• Daylight, noise and activity during the day

• Darkness, quietness and less activity during the Big Sleep at night.

For all of us, and also for your toddler, light falling on the back of our eyes has by far the most powerful effect upon the settings of the body clock.

Here are useful things to know about working with your toddler's body clock to keep sleep healthy in your family.

• The most important way to set our body clock is to get up at the same time each day. You might hear that regular bedtimes are essential for healthy childhood sleep, but this misunderstands the sleep science! A regular get up time is essential for healthy sleep, at least if any sleep problems have come up. Bedtimes then follow the rise of sleep pressure.

• It's normal for toddlers to wake a few times in the night. (This can be quite upsetting to hear. You might start to wonder how you'll ever get through! You can find out more here.)

• A very fragmented sleep pattern, which I refer to as excessive night waking, is the most common sign of disrupted body clock settings. If your toddler is waking excessively at night, there are things you can do to reset your toddler's body clock so that it is in better sync with your own. This means you need to understand how your toddler's sleep pressure works, too.

• When you have a toddler, evening is best thought of as an extension of daytime. In climates with long winter nights, night-times are less likely to be disrupted with excessive waking if the evenings are filled with light (even if artificial), noise and activity. This keeps your little one dialled down as his sleep pressure rises.

• It takes a couple of weeks to reset your toddler's body clock.

These things might sound surprising to hear, and quite different to other approaches. But they are the key steps to The Possums Sleep Program.

You can find out more about the science of the body clock here.

Selected references

Akacem LD, Simpkin CT, Carskadon MA, Wright KP, Jenni OG, Achermann P, et al. The timing of the circadian clock and sleep differ between napping and non-napping toddlers. Plos One. 2015;10(4):e0125181.

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.