What is sleep for?

Dr Allan Hobson, psychiatrist and titan of dream research, posited that:

“Sleep is of the brain, by the brain and for the brain”.

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It is the quiet place our biological computer retreats to contemplate the days events. To build insight and long-term memory and to prepare for the coming day.

The “of the” and “by the” components of Prof Hobson's adage are interesting but deeply technical. The circuitry underlying sleep is complex and how the delicate structures in our brainstem, thalamus and cortex co-ordinate our daily unconscious processes are not fully known.

However, “for the”... What benefits does sleep convey? Why do we sleep? Has been made much clearer by years of fantastic research which we can boil down into a few key themes:

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Scheduled downtime for maintenance

The human brain contains around 86 billion neurons and just as many support cells, making up a total of 170 billion cells. Of these, about 16 billion neurons are in the cerebral cortex, which is where most of our complex thinking, decision-making, and consciousness occur.

Each cortical neuron (pyramidal cell) connects to around 30,000 other neurons, forming a vast network of about 160 trillion connections—a biological supercomputer operating at a trillion bits per second.

This high-powered system is energy-intensive, using about 25% of our daily calorie intake—the same amount as our entire muscles and skeleton combined, despite weighing only 1.5kg. But burning that much energy produces a lot of metabolic waste. Unlike other organs, the brain is sealed off by the blood-brain barrier, meaning it can’t easily clear waste into the bloodstream during the day.

When we’re awake and thinking, blood flow increases to deliver oxygen and nutrients, crowding out waste clearance pathways. Over time, toxic byproducts—such as the proteins linked to Alzheimer’s disease—begin to accumulate.

At night, as brain activity slows, the glymphatic system kicks in, flushing out waste more efficiently. Sleep allows the brain to clear more waste than it produces, preventing long-term buildup. Chronic sleep deprivation, particularly in shift workers, disrupts this process and has been linked to increased risks of cancer, dementia, and heart disease.

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Motor learning and skill acquisition: Training while you sleep

For athletes, musicians, and even professionals in technical fields, sleep is essential for refining motor skills and procedural learning.

During slow-wave sleep, the brain replays and strengthens muscle memory, ensuring that new physical skills are deeply ingrained. This is why professional athletes and high-performance workers prioritise good sleep—it enhances reflexes, precision, and coordination. Whether it’s learning a new sport, playing an instrument, or even improving a manual task at work, a full night’s sleep is as important as practice itself.

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Benefits outside brain functioning:

Immune system support: Sleep as the body’s defence mechanism -  We often feel the need to sleep more when we’re sick—and for good reason. During deep sleep, the body releases cytokines, proteins that regulate immune function and help combat infections.

Research has shown that sleep-deprived individuals are more susceptible to illnesses like colds, flu, and even chronic inflammatory diseases. In workplace settings, chronic sleep deprivation contributes to absenteeism and prolonged recovery times from illness, making sleep a crucial factor in workforce health and productivity.

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Metabolic regulation: The link between sleep and weight gain - Sleep is a key regulator of metabolism and appetite, and chronic sleep deprivation has been directly linked to weight gain and metabolic disorders. Poor sleep disrupts ghrelin and leptin, the hormones responsible for hunger and satiety, leading to increased cravings—particularly for high-calorie, sugary foods.

In fact, sleep deprivation reduces insulin sensitivity, increasing the risk of type 2 diabetes. Given the rising concerns around workplace wellbeing and obesity-related conditions, understanding how sleep influences metabolic health is essential.

At MOAI Health, we help organisations understand and mitigate the impact of poor sleep on workplace performance, mental resilience, and long-term health. Through evidence-based training, we support businesses in addressing sleep-related risks—whether from shift work, stress, or modern work patterns. Investing in sleep health isn’t just about wellbeing—it’s about building safer, more productive, and more resilient teams. Get in touch to learn how we can help.

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References

1. Herculano-Houzel, S. (2009). The human brain in numbers: a linearly scaled-up primate brain. Frontiers in human neuroscience, 3, 857.
2. Megías, M., Emri, Z., Freund, T. F., & Gulyás, A. I. (2001). Total number and distribution of inhibitory and excitatory synapses on hippocampal CA1 pyramidal cells. Neuroscience, 102(3), 527–540. https://doi.org/10.1016/s0306-4522(00)00496-6
3. Tang, Y., Nyengaard, J. R., de Groot, D. M. G., & Gundersen, H. J. G. (2001). Total regional and global number of synapses in the human brain neocortex. Synapse, 41(3), 258–273. https://doi.org/10.1002/SYN.1083
4. Zhang, J. (2019). Basic Neural Units of the Brain: Neurons, Synapses and Action Potential. https://arxiv.org/abs/1906.01703v1
5. Hobson, J. A. (2005). Sleep is of the brain, by the brain and for the brain. Nature 2005 437:7063, 437(7063), 1254–1256. https://doi.org/10.1038/nature04283
6. Heymsfield, S. B., Thomas, D. M., Bosy-Westphal, A., & Müller, M. J. (2018). The anatomy of resting energy expenditure: body composition mechanisms. European Journal of Clinical Nutrition 2018 73:2, 73(2), 166–171. https://doi.org/10.1038/s41430-018-0319-3
7. Roenneberg, T., & Merrow, M. (2016). The Circadian Clock and Human Health. Current Biology : CB, 26(10), R432–R443. https://doi.org/10.1016/J.CUB.2016.04.011
8. Albrecht, U., & Ripperger, J. A. (2018). Circadian Clocks and Sleep: Impact of Rhythmic Metabolism and Waste Clearance on the Brain. Trends in Neurosciences, 41(10), 677–688. https://doi.org/10.1016/J.TINS.2018.07.007/ASSET/CFFABA6C-5E0C-4604-8B02-3A31BAFF23D6/MAIN.ASSETS/GR3.SML
9. Besedovsky, L., Lange, T., & Born, J. (2012). Sleep and immune function. Pflugers Archiv European Journal of Physiology, 463(1), 121–137. https://doi.org/10.1007/S00424-011-1044-0/FIGURES/4
10. Singh, T., Ahmed, T. H., Mohamed, N., Elhaj, M. S., Mohammed, Z., Paulsingh, C. N., Mohamed, M. B., & Khan, S. (2022). Does Insufficient Sleep Increase the Risk of Developing Insulin Resistance: A Systematic Review. Cureus, 14(3), e23501. https://doi.org/10.7759/CUREUS.23501

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