Sleep · 5 min
Sleep: the foundation of healthspan
If sleep were a drug, every clinician would prescribe it. It improves insulin sensitivity, lowers blood pressure, consolidates memory, regulates appetite, dampens inflammation, and clears metabolic waste from the brain. And yet roughly one in three adults consistently sleeps less than six hours a night — a dose we now know carries measurable risk.
What sleep is actually doing
Sleep is an active, structured process. Across the night you cycle through light NREM, deep slow-wave sleep, and REM. Slow-wave sleep is when growth hormone peaks, blood pressure drops, and the glymphatic system — the brain's waste-clearance pathway — flushes metabolic by-products including beta-amyloid. REM is when emotional memory is consolidated and the prefrontal cortex is recalibrated.
Lose the last two hours of sleep and you disproportionately lose REM. Lose the first two and you lose deep sleep. There is no version of 'catching up on the weekend' that fully restores either.
The cardiometabolic cost of short sleep
Sleeping less than six hours a night is associated with a 13% higher risk of all-cause mortality and a clear increase in coronary heart disease, type 2 diabetes, and hypertension. A single night of restricted sleep reduces insulin sensitivity by around 25% in healthy adults — a metabolic profile that begins to look pre-diabetic.
Appetite hormones shift too: ghrelin rises, leptin falls, and you eat, on average, several hundred extra calories the next day, weighted toward refined carbohydrate.
The cognitive and emotional cost
Chronic short sleep is now considered a modifiable risk factor for dementia. Disrupted slow-wave sleep impairs glymphatic clearance of amyloid-beta, and longitudinal data link consistently short sleep in midlife to a roughly 30% higher risk of later dementia.
On a shorter horizon: one poor night amplifies amygdala reactivity by around 60%, blunting the prefrontal brake on emotion. Most of what we call 'a bad mood' is, biologically, a sleep-deprived brain.
What good sleep actually looks like
Aim for 7–9 hours in bed, with a regular wake time (the single most powerful circadian anchor), morning daylight within an hour of waking, a cool dark room, and a clear gap between the last meal or alcoholic drink and sleep. Alcohol in particular fragments the second half of the night and suppresses REM, even when it helps you fall asleep.
What to do this week
- Set a fixed wake time, seven days a week, and protect it.
- Get 5–10 minutes of outdoor light within an hour of waking.
- Stop eating three hours before bed; stop drinking alcohol three hours before that.
- Cool the bedroom to 17–19°C and remove the phone from arm's reach.
- If sleep is consistently broken, ask for a screen for sleep apnoea — it is widely missed.