Deep Sleep (Slow-Wave Sleep)

Slow-wave sleep is when the pituitary releases the majority of nightly growth hormone, muscle and bone repair peaks, and the glymphatic system flushes metabolic waste — including amyloid-beta — from the brain. Most adults need 60–110 minutes per night, and it declines roughly 2% per decade after 30. Alcohol, late meals, high evening temperature, and evening high-intensity exercise are the most common suppressors; consistent wake times, cool rooms, and morning daylight are the most reliable boosters.