In deep sleep tissue is repaired, growth hormone released and the brain cleaned; in REM sleep memories are sorted. What the sleep stages do, what disturbs them and how to get more deep sleep, without a gadget.
In short
- Deep sleep sits in the first half of the night and repairs muscle, immune system and brain; REM sleep sits in the second and sorts memories and emotions.
- Alcohol, late meals, heat and caffeine reduce deep sleep; movement during the day, cool temperatures and a regular rhythm increase it.
- From 40 deep sleep declines; strength training and endurance counter that.
- The glymphatic system flushes waste from the brain at night; chronic sleep deprivation is a dementia risk.
The stages of a night
Sleep runs in cycles of about 90 minutes, four to six per night. Each cycle has light sleep, deep sleep and REM sleep, the dream sleep. In the first half of the night deep sleep dominates, in the second REM sleep. That is why going to bed late costs mainly deep sleep and getting up early mainly REM. Both are irreplaceable, and neither can be caught up like a missed meal.
What happens in deep sleep
The body releases most of its growth hormone, which repairs muscle, bone and skin. The immune system forms memory cells and strengthens its response to pathogens and vaccinations. Blood pressure falls by 10 to 20 percent, the heart rests. And the brain cleans itself: in deep sleep the spaces between cells widen and the glymphatic system flushes out waste like beta-amyloid, which stays in the brain in Alzheimer’s. A single night awake measurably raises the amyloid level.
What happens in REM sleep
The brain sorts the day’s memories, links new with known and defuses emotional experiences: what is processed in REM sleep weighs less the next day. Whoever loses REM sleep by getting up too early or drinking alcohol is more irritable, learns worse and has more anxiety. REM sleep is also why sleeping on a problem really helps.
The disruptors
Alcohol is the biggest: it suppresses REM sleep and fragments the second half of the night. Caffeine in the afternoon reduces deep sleep by up to 20 percent even if you fall asleep. Late heavy meals keep digestion and body temperature high, which must fall for deep sleep. A warm bedroom above 20 degrees Celsius. Sleep apnea that chops deep sleep with breathing pauses. And stress that keeps the nervous system on alert.
Getting more deep sleep
Movement during the day is the strongest amplifier: strength training and endurance raise the deep sleep share of the following night. A warm bath or shower one to two hours before bed lowers body temperature afterwards and helps you drop into deep sleep. A cool, dark room. A regular rhythm. No alcohol, no late coffee, an early dinner. And enough time: whoever sleeps only six hours loses mainly the REM sleep of the morning.
Try it
Sleep CalculatorWhen do you have to get up? The best bedtimes by 90-minute cycles, or the other way round: when you should wake up.Caffeine CalculatorCoffee, espresso, tea, cola, energy drink with time: how much caffeine is still in your blood at bedtime, as a curve.Blood Alcohol CalculatorDrinks, weight, sex, time: your blood alcohol after Widmark, when you are sober again and what the evening costs your sleep.Frequently asked questions
How much deep sleep is normal?
About 15 to 25 percent of sleep time, so 60 to 100 minutes in seven hours. The share falls with age. Trackers estimate it imprecisely; the better question is whether you are rested in the morning.
Can I catch up on deep sleep?
After a short night the body prioritizes deep sleep the next night at the expense of REM. Chronic deficit is not offset that way.
Does magnesium help deep sleep?
With deficiency it can improve sleep quality, otherwise the effect is small. Movement, cool temperatures and rhythm work more strongly than any supplement.
This article is general information and not medical advice. If you have symptoms or existing conditions, or before changing any medication, talk to your doctor.
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