What a circadian rhythm is
A general overview of the daily ups and downs in alertness, sleep and other processes in the body.
Topics
Topics and situations
Your daily rhythm touches almost everything: when you feel sleepy, when it's easier to focus, how you handle a night shift or a trip across several time zones. To keep things clear, we have sorted the guide's topics into five groups. Each group briefly explains the essentials and points to sections where you can read more.
A rhythm isn't a rigid timetable but the body's habit of expecting certain things at certain times. A habit can be gently reset.
How this section works: we describe everyday situations that throw off the daily rhythm and the general principles of routine, light and sleep. We do not list signs for self-diagnosis, name remedies or suggest treatment plans.
How the inner clock works
Circadian rhythms are internal rhythms with a period of about one day. Light is their main external cue.
Light as the main cue
Why morning light supports your rhythm, while bright light late in the evening can shift it.
Melatonin, the hormone of darkness
A hormone produced mainly during the dark hours; anything about supplements is for your doctor only.
Routine and chronotype
Some people find it easy to get up at dawn, others think best in the evening. That's normal, but a routine still matters.
Early birds and night owls
What a chronotype is and why a tendency toward early or late sleep can change with age.
Teens and older adults
Teens' rhythms often drift later, older adults' drift earlier; routines are worth adjusting gently.
Weekdays and weekends
The downside of sleeping in until noon, and what is called “social jet lag.”
Shift work and travel
When work or travel requires you to be awake at night, your inner clock falls out of step with your surroundings.
Night and rotating shifts
How to plan sleep, light and a darkened bedroom when your work falls at night.
Flying across time zones
Why adjusting is often harder after flying east, and what helps you settle in.
Daytime sleepiness
When tiredness after shifts or trips is a reason to talk with your own doctor.
Northern latitudes and the seasons
The farther north you go, the more the length of daylight changes over the year.
Polar night
How to keep a routine when the sun doesn't rise above the horizon for weeks.
Polar day
How to darken the bedroom and keep your usual bedtime when it's light around the clock.
Short winter days
How darkness affects energy and why low mood that persists is a reason to see a doctor.
Checking the facts
A lot is written about sleep, and not all of it holds up to scrutiny.
News about sleep and body rhythms
How to tell a mouse study from human research and a survey from an experiment.
Reliable sources
What this guide relies on and why it contains so few numbers.
Glossary of terms
Chronotype, circadian misalignment, sleep hygiene and other terms in plain language.
Catalogue of articles in English
This is where standalone articles about daily rhythms, light and sleep schedules in everyday life will appear, written for English-speaking readers. Each article is checked against the same rules as the sections of the guide.
- Aion 2 sealed dungeons: Useful Resources and Planning Tips
Which resource answers which question about Aion 2 sealed dungeons, how to build a one-page run card, and where paid assistance differs from in-game play.
- Aion 2: Raids — Ecosystem Overview
Who shapes Aion 2 raids, from the developer and guilds to guide writers and carry services, plus player prerequisites, rules to know and realistic alternatives.
- A practical guide to Aion 2 kinah farming: Player Experience
What Aion 2 kinah farming feels like over a first evening, week and month, how the main options compare, and how boosting services fit alongside in-game play.
- Gaming Services, Player Time and Progression: An Industry Overview — A Practical Reference #1
A six-criterion framework for weighing gaming services against your time: goals, hours, providers, rules, market signals and claims, each with a checklist.
- GTA 6 Gameplay Coaching and Skills: Practical Guide
Hands, eyes and head: a three-layer way to build open-world action skills before GTA 6, and how to judge a coaching offer without risking your account.
Topics in progress
- Getting back on schedule after the clocks change for daylight saving time
- Making the most of daylight during dark winter commutes
- Setting up a bedroom for daytime sleep after a night shift
- Coast-to-coast trips: adjusting to a three-hour time difference
- Keeping a sleep diary before a visit to your doctor
- Teens, early school start times and a workable weeknight routine
Editorial rules
- Articles in this catalogue are written separately for each language version and are not translations.
- Some articles link to third-party websites, including gaming services; we do not control their content, prices or terms.
- We do not publish advertising for clinics, specialists, medicines, devices or apps, rankings, prices or reviews.
Read next
- Prevention
Everyday habits for a steady rhythm: a consistent wake-up time, morning light, movement, a quiet evening and seeing a doctor in good time.
- Approaches
How to plan sleep and light around shift work, after a flight and above the Arctic Circle, who to see and how to keep a sleep diary.
- Glossary
Body rhythm terms in plain language: from circadian rhythm and chronotype to the sleep diary and polar day.
- Research
How to read news about sleep and body rhythms: bold headlines, mouse vs. human studies, surveys vs. experiments, and who paid for it.
Sources
- Nobel Committee — the 2017 Nobel Prize in Physiology or Medicine
- American Academy of Sleep Medicine — recommendations on adult sleep duration (2015)
This guide draws on the Nobel Committee's announcement of the 2017 prize, the recommendations on adult sleep duration and the WHO guidelines on physical activity as they were available when the texts were written. Scientific understanding of sleep rhythms keeps evolving, so questions about your own health are best discussed with a doctor.