Circadian Rhythm and the Quiet Order of the Day

Sleep problems do not end in the morning

A sleepless night often does not end with the morning alarm. The next day, it can be harder to concentrate, easier to feel tense or exhausted, and even ordinary pain may feel more intrusive. When this state continues, trouble falling asleep, a lower mood, and physical discomfort can begin to reinforce one another.

Researchers at the University of Missouri examined precisely these connections by analyzing the everyday functioning of both people with insomnia and people who slept well. At the center of their interest was the regularity of the day: similar times for waking up, eating, being active, interacting with other people, and going to sleep.

As expected, participants with insomnia reported pain and depressive symptoms more often. At the same time, regardless of sleep quality, people who described their day as more regular reported lower levels of pain and fewer depressive symptoms. This pattern appeared both among participants with insomnia and among those who slept well. The study was observational, however, so it points to a link between daily regularity and well-being. It does not prove that one directly causes the other.

The body needs points of reference

The researchers connect this relationship with the circadian rhythm — the internal system according to which the human body functions. It measures cycles lasting roughly 24 hours and influences sleep, wakefulness, body temperature, hormone release, appetite, and mood, among other things.

Light is the most important signal for this system, but the body also uses information from everyday behavior. The timing of the first meal, physical activity, the start of work or study, meetings with other people, and evening rest can all matter.

If we consistently wake up, eat, work or study, interact with others, and go to sleep at similar times, these time cues help synchronize our internal biological clocks,

explains Eunjin Tracy, a co-author of the study from the University of Missouri.

A daily rhythm may therefore be more than a matter of good organization. It can work like a set of recurring messages for the body. When these signals change frequently — for example, when we wake up early during the week but sleep until noon at the weekend, or eat lunch at 2 p.m. one day and at 8 p.m. the next — maintaining a stable circadian rhythm may become more difficult.

Weekend “jet lag” unsettles the body

Researchers use the term “social jet lag” to describe the gap between a person’s biological rhythm and the schedule imposed by work, school, and social life. We do not need to travel across time zones to experience it. A clear shift in sleep and wake times between working days and days off is enough.

When we regulate our circadian rhythm well, the body functions well. But when it becomes too strongly disrupted, it no longer works as smoothly,

Tracy emphasizes.

A link between social jet lag and mental well-being also appears in a meta-analysis published in 2025 in BMC Psychiatry. Its authors analyzed 8 studies covering more than 148,000 people aged 10 to 24. Participants whose sleep rhythm differed by at least 2 hours between school or work days and days off showed depressive symptoms more often. Still, because the studies were observational, they cannot determine what is cause and what is effect.

Health problems may begin in the rhythm of the whole day

The findings suggest that health may depend not only on how long we sleep, but also on the rhythm of the whole day. Sleep problems do not always concern only what happens after we get into bed. They may relate to whether the day has relatively stable points of reference, and whether mealtimes, work, activity, and rest change radically from one day to the next.

Flexible schedules, remote work, weekend shifts in sleep, and irregular meals do not automatically mean worse well-being. They may, however, make it harder to synchronize the circadian rhythm.

This does not mean that every irregular weekend leads to depression, or that eating breakfast at the same time every day will solve the problem of pain. Depression, insomnia, and chronic symptoms have biological, psychological, social, and medical causes, and treatment may require specialist help. The Missouri study simply draws attention to an often overlooked element of everyday life: the relative predictability of the day, and the circadian rhythm that quietly depends on it.

Read this article in Polish: Nie tylko sen. Organizm lubi, gdy dzień ma rytm