Within all of us are a number of biological clocks which link together via a master clock in the brain to produce and manage something called our circadian rhythm. Essentially the circadian rhythm runs in the background of our brain, cycling us through each 24-hour period via a series of physical, mental and behavioural changes which prime us for sleep at certain times. Besides the internal drivers, our circadian rhythm is influenced by a number of environmental cues. The most notable one is light, but noise and habits and behaviour such as mealtimes also play a part. These factors combine and enable our circadian rhythm to guide us through a daily cycle that helps to determine our sleep pattern.
Our circadian rhythm is given a significant helping hand by our body’s production of a hormone called melatonin, which both makes us feel sleepy and improves the quality of our sleep. Melatonin is only secreted in low levels of light – which is why we sleep best when it is dark. Whilst natural daylight inhibits the body’s ability to produce melatonin, so does the light emitted from screens such as televisions, smartphones and tablets. For this reason, and to give your little one the best chance of the physical mechanisms available to him helping to prime him for sleep, it is best to avoid having such devices on where your child can see them, for at least a full hour (ideally two) prior to commencing their bedtime routine.
For similar reasons, your little one will have the best chance of settling to sleep quickly in a room that is as dark as you can get it – if 10/10 is a total blackout, aim for at least 8/10. Babies are rarely afraid of the dark, not least because the womb-environment is pitch black so rarely will a nightlight aid sleep. For an older child who expresses a fear of total darkness, a dim nightlight with a red bulb is the least likely to hinder sleep whilst offering enough light to be comforting.
The other hormone to be aware of in the context of sleep is cortisol, which along with melatonin has an influence on our circadian rhythm. One of the many functions of cortisol is to make us feel alert and as its levels rise in the early hours of the morning, our bodies begin to drive towards wakefulness. If our little one’s schedule is working well, their cortisol levels will be low in the evening and first two-thirds of the night. However, one important feature of cortisol is that it helps us to “keep going” when we are very tired. When babies have either not had enough daytime sleep, or have been awake longer than is comfortable for them in one stretch, they will have released more cortisol to stay awake and functional. Whilst this can initially make a little one appear cheery and engaged, the hormone response will make them wired and over time they are likely to become agitated and cranky. Unfortunately, the more cortisol a little one has coursing through their veins, the harder it is for them to calm down and fall asleep.
Whilst an adult body will elicit the same cortisol response (consider whether you’ve ever felt exhausted after a long-haul flight with little restful sleep only to feel you gain a “second wind” on arriving at your fabulous hotel!), babies and children find it incredibly difficult to remove the hormone from their bodies. One of the few methods at their disposal is movement which is why overtired babies may wriggle and may fight being held. Another mechanism for excreting cortisol is through yawning and this can often catch parents out – whilst a single yawn (if spotted!) may indeed be an early sign of sleepiness, multiple yawns are more likely to indicate that the overtired response is already in play and subsequently that the optimal window for getting our little one down has passed.
If you notice that your baby becomes irritable at a similar time each evening, it’s likely that his natural bedtime sits a little before that time. By getting your little one down in good time you have the best scope to avoid or limit the cortisol response. Similarly with an older baby or toddler, if you notice a pattern with giddy behaviour occurring in the late afternoon or evening, it’s a strong sign that their daytime sleep isn’t optimised and/or that bedtime needs to move a little earlier.
Throughout a 24-hour period, the hypothalamus in our brain regulates our body temperature. Our circadian rhythm primes us to sleep when our core temperature is dropping. This means that as a child’s natural bedtime is approaching, the brain will be gradually adjusting their body temperature downwards which makes falling asleep easier. If you have ever struggled to fall asleep in unusually hot weather you have experienced what happens when this process is interfered with! To enable the body to cool to the optimal temperature for sleep, it is sensible to avoid particularly energetic play, or other activities which are likely to leave your little one hot, in the run up to bedtime. If a bath is part of the bedtime routine, always check the temperature of the water with a thermometer, both for safety and to avoid inadvertently hindering the body’s bedtime preparations. When the weather is especially warm you may find that actually reducing the temperature of the bath by a couple of degrees helps your little one settle to sleep more easily at bedtime.
It can be tempting to overdress babies at bedtime as their ideal room temperature of around 18 degrees can feel cool to parents! However, not only does wrapping a little one up too warmly make it harder for them to settle to sleep, it also increases the risk of Sudden Infant Death Syndrome so it always advisable to resist the temptation to bundle a little one up too tightly.
I frequently talk to parents who are confused as to why their child settles beautifully at bedtime yet struggles to resettle at numerous night-wakings. Often the little one is being put down awake at bedtime and the parents, entirely sensibly, believe he is able to self-settle. On digging a little deeper, it usually transpires that the child is falling asleep in ten minutes or less. As crazy as it sounds, that’s too quickly!
“Sleep onset latency” is the time taken to fall asleep and the ideal is 15-20 minutes. When a little one falls asleep more quickly than this there are two issues. Firstly, even though they may have gone into their sleep space with their eyes open, and even vocalising, they were so tired that they haven’t had to initiate sleep for themselves – tiredness has scooped them up and taken them over the line to sleep. As such, whilst they have more skill around self-settling that a little one who is put down already out-for-the-count, when the edge is taken off their tiredness by the first few hours of sleep, they don’t have the requisite skills to resettle without help. This is compounded by them effectively “crashing” into sleep, skipping the lighter stages of sleep we transition through when we fall asleep more gradually. The consequence of this is that the child is then likely to find it harder to navigate through the different states of sleep later in the night, which inevitably leads to more frequent wake-ups.
Almost all children are natural “larks” which means they rise for the day relatively early (typically between 6 and 7am). Consequently, they are ready for bed in the early evening. Most little ones need an overnight sleep of around 11-12 hours meaning that a bedtime between 6 and 8pm is appropriate for babies, toddlers and pre-schoolers. Bedtime is far easier for a parent to adjust than a little one’s wake up time which is more fixed due to the lark chronotype so this is why it makes sense to work backwards from the start of the little one’s day to determine the ideal bedtime. When a little one misses their optimum bedtime-window, they have missed the point when their bodily processes were best aligned to make settling to sleep as stress-free as possible.
As you can see, the body is pretty remarkable and whilst it may not feel like it at times, a little really does want to be asleep at night! When a child’s daytime is managed in a way that supports the numerous functions that prepare them for restful sleep, a family is well on their way to sleep success.