What is sleep, anyway?

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.

What is sleep, anyway?

Sleep is a mysterious physical and mental state of profound rest and relaxation, still not well understood by scientists, yet necessary for human survival. I think of sleep as a complex biological wave which washes over us to heal and renew our body and soul. As adults, when all is going well and we are living more or less in sync with our body's sleep needs, we need only quieten our minds and surrender.

What do evolutionary anthropologists tell us about human sleep?

Throughout human history and across the cultures of the global majority, adult sleep has been

• Social, occurring in close proximity to other humans, which has included babies and toddlers sleeping in close contact with the breastfeeding mother's body

• Flexible and adaptive

• Very diverse, both within the one individual over time, between individuals, and across cultures

• Broken, with wakeful periods during the night.

There are four main features of post-industrial societies which impact profoundly on adult sleep. They arise from a mismatch between our environments of evolutionary adaptedness and our contemporary worlds.

1. With the marvellous advent of electric lighting over the past one hundred years, we have normalised high levels of night-time activities and compressed the amount of time we are willing to allocate for sleep. As a result, unrealistic beliefs about 'healthy' sleep have become widespread. Unrealistic beliefs about sleep worsen sleep.

2. Sleep has become pharmaceuticalised for some of us who have been distressed by poor sleep. Because ceasing hypnotic medications may result in a period of extremely disrupted sleep, these pharmaceuticals are typically addictive.

3. Shift workers, who provide essential services for the benefit of our society, live with profoundly and repeatedly disrupted circadian rhythms, which has physical and mental health impacts. Organising shifts so that these impacts are minimised is a matter of workers' rights.

4. Our increased body weights, typical of contemporary societies, can result in obstructive sleep apnoea, which also profoundly disrupts sleep.

I have the view that governments and health systems need to more seriously address these four problems which impact on sleep health through innovative prevention and education. But today, the education people tend to hear about sleep focusses on the bad short- and long-term effects of poor sleep, which fosters a frightened and controlling psychological relationship with our own sleep. This increases adult sleep anxiety, and doesn't help sleep.

How to shape your relationship with sleep for the rest of your life

Human sleep is a complex adaptive biological system. In fact, it's not clear how much the increased inflammatory effects associated with sleep problems are due to the disruptive effects of chronic stress and anxiety (high levels of sympathetic nervous system activity) upon adult sleep, rather than lack of sleep itself.

It seems to me that it's best for us as individuals to shift our focus away from worrying about how much sleep we are getting at night, which can interfere with our capacity to sleep easily. Instead, we could focus on creating a rich, full and meaningful life. This includes leaving an ample portion of the day, coinciding with night-time, for sleep, rest and self-nurturance, without the expectation that it be entirely filled with sleep, since some nights we'll sleep more, some nights we'll sleep less.

Here are things to know about sleep which I hope you'll find useful.

• Getting up at the same time each morning, with early morning sunlight exposure if possible, is the most powerful way to protect your sleep patterns, right throughout your life.

• Alcohol might seem to bring on drowsiness in the evening, but worsens sleep duration and consolidation over time.

• Caffeine (coffee, green tea) late in the day can make it more difficult to fall asleep.

• Excessive blue light exposure before bedtime may impact negatively upon sleep.

• Regular exercise helps with sleep. Evening exercise doesn't interfere with sleep, as long as you avoid high intensity exercise in the hour before you go to bed.

• Durations of sleep are variable in the same individual from night to night (even in adults who aren't caring for babies or toddlers). It's normal to wake in the night (even when you don't have a baby or small child in the home).

• Reading a book in bed before going to sleep has been linked with better sleep. (This research didn't investigate parents with babies and toddlers.)

• Although there may be a genetic component to our preferred circadian clock settings, we can reset our body clocks to suit our changing life circumstances.

• Sleep needs decrease as adults age, with decreased sleep pressure, more wakings at night and less total sleep. This is biologically normal. Although the time taken to go to sleep or get back to sleep doesn't particularly change with age, older adults can take longer to recover from changed circadian settings.

A word about dreams

At night, in sleep, our body speaks a primordial language which we might remember on waking, and which I try to pay attention to, at least at times, in myself. This language of images and emotions and physical sensations – the dream – is a portal into the human soul, reminding us that we live in the midst of mysteries much greater than our mind can ever really comprehend.

Remembering a dream is like reading a poem. It’s like paying attention to a fine painting or a piece of cinema, made up by my own body and mind in response to my life, but outside my control. My dream speaks to me in an embodied, imaginal language while I sleep. It's often raw and wild, throbbing with terror or wonder or longing. My dream responds to my deepest truths, tells me the stories of my body and soul's experience, narrates my own life myths. Often I find this helpful, sometimes encouraging, sometimes a warning, always a celebration of the richly poetic mystery of being alive, and of the poetic basis of our stunningly complex human minds.

Recommended resources

Why you don't need to think about sleep architecture

Evolutionary biology and cross-cultural studies tell us that our little one's sleep can be easy (once you know how)

The NDC evolutionary perspective on positional plagiocephaly, motor development and sleep

Selected references

Ashbrook LH, Krystal AD, Fu Y-H, Ptacek LJ. Genetics of the human circadian clock and sleep homeostat. Neuropsychopharmacology. 2020;45:45-54.

Coveney C, Williams SJ, Gabe J. Medicalisation, pharmaceuticalisation, or both? Exploring the medical management of sleeplessness or insomnia. Sociology of Health and Illness. 2019;41(2):266-284.

Dzierzewski JM, Donovan EK, Kay DB. Sleep inconsistency and markers of inflammation. Frontiers in Neurology. 2020;11:1042.

Finucane E, O'Brien A, Treweek S. Does reading a book in bed make a difference to sleep in comparison to not reading a book in bed? The Peope's Trial - an online, pragmatic, randomised trial. Trials. 2021;22:873.

Li J, Vitiella MV, Gooneratne NS. Sleep in normal aging. Sleep Medicine Clinics. 2018;13(1):1-11.

McKenna JJ, Gettler LT. There is no such thing as infant sleep, there is no such thing as breastfeeding, there is only breastsleeping. Acta Paediatrica. 2015;105(1):17-21.

Messman BA, Wiley JF, Yap Y. How much does sleep vary from night-to-night? A quantiative summary of intraindividual variability in sleep by age, gender, and racial/ethnic identity across eight-pooled datasets. Journal of Sleep Research. 2022;31(6):e13680.

Moore, Thomas. Care of the soul in medicine. 2010. Random House.

Samson DR. The human sleep paradox: the unexpected sleeping habits of Homo sapiens. Annual Review of Anthropology. 2021;50:259-274.

Silvani MI, Werder R, Perret C. The influence of bluelight on sleep, performance and wellbeing in young adults: a systematic review. Frontiers in Physiology. 2022;13:943108.

Stutz J, Eiholzer R, Spengler CM. Effects of evening exercise on sleep in healthy participants: a systematic review and meta-analysis. Sports Medicine. 2019;49:269-287.