Sleep feels like a waste of time but, if it wasn’t important, we wouldn’t spend a third of our time doing it. 

Interestingly, humans sleep less than other mammals, and this is thought to be because we have protected our sleeping environment both behaviourally (through sentinel behaviours) and physically (through creating protected dwellings). This has allowed us to sleep more deeply and with less interruptions than other animals, increasing our sleep quality per unit time.[1]

Adequate sleep underpins our physical and cognitive function, in the immediate and longer term. During sleep, our bodies and brains clean, repair and grow, and we encode and make sense of experiences and new information. In fact, chronically inadequate sleep increases our all cause mortality by 13%.[2] 

Yet, 30% of American adults suffer from ‘insufficient sleep syndrome’, a ‘voluntary’ state of chronically reduced sleep to accommodate lifestyle or work demands, and sleep problems have been declared a global public health issue.[3]

It’s recommended that adults get between 7-9 hours of sleep.[4] Individual requirements vary, but it is rare to need less... Rarer than being struck by lightning, according to Matthew Walker.[5] 

We sleep in 90 minutes sleep cycles, with more restorative deep sleep at the beginning of the night and more creative, emotionally regulating REM (or ‘dream’) sleep in the second half of the night. We need to sleep deeply enough to get enough deep sleep, and for long enough to get enough REM sleep, see Figure below.

You can read more about sleep in the article I wrote for the Royal College of Surgeons (March 2025) here, or hear more in my Expert Conversation with Dr Caitlin Chasser of The Sleep Project.

This is all well and good, but how do you optimise sleep? 

I’ve divided this topic into: Going to sleep, staying asleep, and waking up refreshed.