The glymphatic system is the brain's lymphatic-equivalent — a network of perivascular spaces along arteries and veins that flush cerebrospinal fluid through brain tissue to clear waste.
Mechanism — Aquaporin-4 channels on astrocyte endfeet enable CSF-interstitial fluid exchange. Activity peaks during deep (N3) sleep, when brain cells shrink and extracellular space expands by ~60%. Clears amyloid-beta, tau, and other waste proteins.
Use case — Protect deep sleep at all costs (cool room, no alcohol within 3 hours, magnesium glycinate, consistent sleep timing). Lateral sleeping position appears to be best for glymphatic flow.
Caveats — Glymphatic flow declines with age — one reason sleep matters more, not less, as you get older. Disruption (alcohol, sleep apnea, fragmented sleep) is linked to increased amyloid accumulation.