Sleep – the silent superhero of our lives

A science-based article on the most important form of human recovery

A science-based article on the most important form of human recovery

Introduction: the half of life that decides everything

About a third of our lives we spend asleep. And exactly this time decisively determines how the other two thirds go: how we feel, how we think, how we recover, how we stay healthy. Nevertheless, sleep is often dismissed as "wasted time" – as a gap between two productive days that should be kept as small as possible.

Science tells a completely different story: sleep is not a passive off-state, but an active, highly complex process in which our body repairs, cleans up, learns and becomes stronger. Anyone who takes good sleep seriously invests in health, performance and quality of life. This article shows what happens during sleep, how to optimise it – and what happens when you neglect it.

1. What does sleeping actually mean?

Sleep is a natural, recurring state of rest in which consciousness, perception and responsiveness are reduced – yet the organism keeps working at full speed. Sleep is an active recovery and regeneration process controlled by the internal biological clock (the circadian rhythm).

While we sleep, important programmes run in the body: cellular repair processes are switched on, fat and sugar metabolism is optimised, blood pressure is regulated long-term and the brain processes the impressions of the day.

Sleep is therefore far more than "lights off" – it is the nightly maintenance of our entire system, from the muscles to the immune system to the brain.

2. The sleep stages: a journey through the night

Our sleep is not one single uniform phase, but follows a rhythmic pattern of different stages that repeat in sleep cycles. A typical cycle lasts about 90 minutes in healthy adults and repeats four to seven times per night.

Two large categories are generally distinguished:

NREM sleep (non-REM) – the quiet sleep with three stages:

REM sleep (Rapid Eye Movement): the "dream phase" – the brain is almost as active as when awake, the eyes move quickly, but the body muscles are paralysed. REM sleep is crucial for processing emotions and consolidating memory.

Particularly interesting: the distribution changes over the course of the night. Deep sleep takes up more space in the first half of the night, while the REM share increases in the second half. That is why you often feel especially unrested after too short a night – important cycles have been cut off.

3. When should you sleep? The power of the internal clock

The ideal sleep time is not arbitrary, but determined by our internal clock – the circadian rhythm that controls many biological processes in a roughly 24-hour cycle, including sleep, energy levels, appetite and mood.

The most important pacemaker is light: it synchronises the internal clock and controls the release of melatonin, the sleep hormone. In darkness the melatonin level rises, in brightness it falls.

Chronotypes: not everyone is set the same way. A distinction is made between "larks" (early risers), "owls" (late risers) and intermediate forms. An ideal sleep rhythm arises when sleep time and duration are matched to the individual chronotype.

The best bedtime: research suggests that falling asleep between 10 and 11 p.m. is optimal for many people – a British study on the ideal bedtime showed links between the time of falling asleep and cardiovascular health.

Regularity is crucial: anyone who sleeps at changing times confuses the internal clock – with consequences for sleep quality and health. Fixed bedtimes and wake times, even at the weekend, are therefore the most effective measure for restful sleep.

4. How long should you sleep?

The National Sleep Foundation recommends 7 to 9 hours of sleep per night for adults aged 18 to 64, and 7 to 8 hours for people over 65.

Interestingly, many sleep experts consider about 7.5 hours optimal for most people – this duration leaves enough room for all the important sleep stages and cycles.

Important: there is no universally valid sleep duration for everyone. Individual sleep needs depend on age, genetics, activity and health. The decisive question is not only "how many hours?", but: do you feel rested in the morning and stay awake and productive during the day? Then your sleep duration fits.

5. Good sleep: what it means for body and mind

The positive effects of good sleep are comprehensively documented:

For the body:

For the brain and psyche:

6. Poor sleep: the underestimated warning signs and consequences

Poor sleep is more than "just being tired". The symptoms affect body and mind equally – and many of them are overlooked or misinterpreted in everyday life.

Typical signs of sleep deprivation:

Chronic consequences: anyone who permanently sleeps too little or poorly risks long-term health damage: increased risk of cardiovascular disease, metabolic disorders such as diabetes and overweight, a weakened immune system and increased susceptibility to psychological strain.

7. The perfect sleep environment: essentials for optimal sleep

Good sleep begins with the right conditions. The good news: you don't need expensive high-tech equipment, but a few proven fundamentals.

Mattress: the mattress is the most important sleep investment. It should match your height, weight and preferred sleep position – independent tests such as those by Stiftung Warentest examine mattresses for different body types in side and back positions. An unsuitable mattress is one of the most common causes of morning back pain.

Pillow: the pillow supports the natural curvature of the spine. Side sleepers especially need an ergonomically shaped pillow that stabilises the cervical spine and prevents neck tension.

Duvet and bedding: breathable materials regulate the sleep climate and prevent night sweating.

Temperature: the ideal bedroom temperature is 16 to 19 degrees Celsius – cool, but not cold.

Darkness: blackout curtains or a sleep mask block disturbing light, because light suppresses melatonin production and keeps us awake.

Quiet: noise disturbs the deep-sleep phases – earplugs or calming sounds can help.

More essentials that make the difference:

8. How, when and where to sleep? The rules of sleep hygiene

Science has clear recommendations for optimal sleep – they are summarised under the term sleep hygiene:

The "where":

The "when":

The "how":

9. Can you sleep too much?

Yes – too much sleep can also be unhealthy. Research shows that not only permanently too short sleep (under five hours), but also permanently too long sleep (over nine hours) increases the general risk of disease.

Several studies point to a link between excessive sleep and various conditions – including metabolic syndrome, cardiovascular disease and a disturbed balance of the hormones that regulate hunger.

Where is the limit? Regularly sleeping more than 9–10 hours per night is considered potentially problematic – especially if you are still tired during the day. In such cases, hypersomnia (pathologically increased sleepiness) may lie behind the increased need for sleep and should be clarified medically.

Important for context: occasional extra sleep after strenuous phases is normal and part of recovery. It becomes problematic when too much is slept permanently – or when the increased need for sleep comes with persistent exhaustion.

10. Conclusion: sleep is the cheapest health measure in the world

Sleep is not a loss of life time – it is the investment that makes all other investments effective in the first place. Whoever sleeps trains their immune system, repairs their cells, consolidates their memory, stabilises their mood and protects their heart.

The formula for good sleep is scientifically clear:

And remember: good sleep does not feel like "wasted time" – it feels like energy, clarity and health the next morning.

Sleep well. It is the most important work your body does.