In short
- Your body runs on a roughly 24-hour cycle called the circadian rhythm.
- A small area of the brain acts as the master clock. Light reaching your eyes is its strongest signal.
- Almost every organ has its own clock, and they stay in step with the master clock.
- Regular wake times, daylight in the morning and dim light at night are the habits most linked to a steady rhythm.
A clock in every cell
"Circadian" comes from the Latin circa diem, "about a day". Over each 24 hours your body temperature, hormone levels, blood pressure and alertness rise and fall in a regular pattern. This happens even if you shut yourself away from daylight. The rhythm comes from inside you.
The timing comes from a loop of "clock genes". During the day, cells make certain proteins. These slowly build up until they switch off the genes that made them. Then they break down, and the cycle starts again. One full loop takes about 24 hours.
In 2017 Jeffrey Hall, Michael Rosbash and Michael Young won the Nobel Prize in Physiology or Medicine for working out this loop, first in fruit flies. The same kind of machinery runs in people.
The master clock
Deep in the brain, just above where the optic nerves cross, sits a cluster of about 20,000 nerve cells called the suprachiasmatic nucleus. It works as the master clock. It sends timing signals out to the rest of the body, partly through the nervous system and partly through hormones.
The liver, gut, muscles and fat all have their own clocks too. The master clock keeps them in step, a bit like a conductor and an orchestra.
Why light matters most
Left to itself, the human clock runs a little long: on average about 24 hours and 10 minutes. So it needs resetting every day. Its main reset signal is light.
Special light-sensing cells in the eye, separate from the ones you see with, report how bright it is straight to the master clock. Bright light in the morning pulls the clock earlier. Bright light late in the evening pushes it later. Daylight outdoors is many times brighter than indoor lighting, even on a cloudy day.
Meal times, exercise and social routines also nudge the clock, but less strongly than light.
What a typical day looks like
| Roughly when | What the body is doing |
|---|---|
| Early morning | Core body temperature is near its lowest, about 2 hours before your usual wake time. Cortisol starts rising before you wake. |
| After waking | Cortisol peaks around 30–45 minutes after waking. Melatonin has fallen to daytime levels. |
| Late afternoon | Core body temperature is near its highest. |
| Evening | Melatonin starts to rise, usually about 2 hours before your habitual bedtime, as long as the light is dim. |
| Night | Melatonin stays high. Temperature falls. |
These are averages. Your own timing depends on your chronotype, whether you lean "lark" or "owl". You can read about chronotypes here or try the 5-question chronotype check.
When the clock and your life disagree
Shift work, long-haul flights and late nights followed by early alarms all pull your daily routine away from your internal clock. Researchers call the weekday–weekend version "social jet lag". It is very common, and studies link it with poorer sleep.
Habits linked to a steady rhythm
- Get up at a similar time every day, weekends included, within about an hour.
- Get daylight early. Ten to thirty minutes outdoors in the first hour or two after waking.
- Dim the lights in the evening, and keep screens away from the bedroom where you can.
- Keep caffeine to the earlier part of the day. See why we say "not after 2 pm".
- Eat at regular times, and avoid big meals right before bed.
Where NOVR fits
We built NOVR as three products for three times of day, because what you might reach for at 7 am is different from 11 pm. That is a timing idea. NOVR does not set or reset your body clock. Light, sleep and routine do that. You can see the 24-hour picture on our science page.
Sources
- Nobel Prize in Physiology or Medicine 2017: Hall, Rosbash and Young, "for their discoveries of molecular mechanisms controlling the circadian rhythm". nobelprize.org/prizes/medicine/2017
- Czeisler CA et al. Stability, precision, and near-24-hour period of the human circadian pacemaker. Science 1999;284:2177–81. doi:10.1126/science.284.5423.2177
- Wittmann M et al. Social jetlag: misalignment of biological and social time. Chronobiol Int 2006;23:497–509. doi:10.1080/07420520500545979
- Roenneberg T, Merrow M. The circadian clock and human health. Curr Biol 2016;26:R432–43. doi:10.1016/j.cub.2016.04.011
This article is general education, not medical advice. Listing a study describes the research only. It is not a claim that NOVR has the same effect.