Sleep Is Not a Passive State
The glymphatic system, circadian alignment, and why consistently under-sleeping accelerates biological ageing.
Sleep is not a passive state. During sleep, the brain's glymphatic system — a waste-clearance network — becomes dramatically more active, flushing out metabolic byproducts including amyloid-beta plaques associated with Alzheimer's disease.
Consistently sleeping fewer than 7 hours per night has been associated with accelerated telomere shortening, elevated inflammatory markers (particularly IL-6 and CRP), impaired glucose metabolism, and dysregulated cortisol rhythms — all established hallmarks of accelerated biological ageing.
The most underappreciated aspect of sleep quality is circadian alignment. It's not just how long you sleep — it's when. Light exposure in the first hour after waking, consistent wake and sleep times, and limiting blue light after sunset are the three highest-leverage interventions supported by the literature.
Deep sleep (slow-wave sleep) and REM sleep serve distinct functions. Deep sleep is when physical restoration occurs — growth hormone release, tissue repair, immune consolidation. REM sleep is when emotional processing and memory consolidation happen. Both are essential.