Your Body Clock & Sleep Timing

Your body runs on an internal clock of roughly 24 hours. It governs when you feel alert, when you feel sleepy, and a long list of processes you never notice.

That clock is set mainly by light. Light in the morning tends to pull your timing earlier. Light late in the evening tends to push it later.

This explains a common frustration. Someone follows every piece of sleep advice, lies down at 10pm, and stays wide awake, because their body clock is not expecting sleep for another two hours. The fix there is timing, not more effort.

What this section covers

How the body clock works, in plain language.
Morning light, and why it is one of the more reliable levers available.
Evening light, screens, and what the research does and does not support.
Chronotypes, and whether a night owl can become a morning person.
Shift work, and the strategies studied for it.
Jet lag, direction of travel, and adjustment before and after a flight.
Social jet lag, the weekday to weekend gap most people carry.
Seasonal changes in light and how sleep timing shifts with them.

What the research actually says

Circadian science is one of the better established areas in sleep. That light shifts the body clock, and that the direction depends on when the light arrives, is well supported and reproduced across many studies.

Consistent wake times are supported for the same reason. A stable wake time anchors the clock more effectively than a stable bedtime does.

Chronotype has a genuine biological component. Someone who naturally runs late is not simply undisciplined, and research on adolescents and school start times has made that point clearly.

Shift work is harder. Reviews find that adaptation strategies help some workers, but no approach fully removes the strain of working against the clock. We report that honestly rather than offering a fix.

Melatonin comes up constantly in this area. Timing appears to matter more than amount in the research, but we do not publish doses or schedules, and that is a conversation for a pharmacist or doctor.

When to talk to a doctor

Some timing problems are recognised sleep disorders and can be assessed properly.

You consistently cannot fall asleep until very late and cannot wake at the time you need to.
Your sleep timing drifts later each day regardless of what you do.
Shift work is leaving you unsafe to drive or unable to function.
You are considering melatonin or any sleep product. Ask a pharmacist or doctor, particularly if you take other medication.
Low mood tracks strongly with the seasons.

Continue reading

The main sleep guide

How sleep works, how much you need, and where to go next.

Sleep hygiene and environment

Light, temperature, noise, and routine, and what holds up.

Tracking and measurement

What your device can see, and what it is guessing at.

Medical disclaimer

This article is for general information only. It is not medical advice, and it is not a substitute for diagnosis or treatment from a qualified healthcare professional. Do not start, stop, or change any medication, supplement, or treatment based on what you read here. If you have symptoms that concern you, contact a doctor. If your symptoms are severe or sudden, seek emergency care.