What is chronobiology? The science of the body's timing

Almost every living thing keeps time. Plants open and close their leaves, birds migrate in season, and our own bodies run on a daily rhythm that shapes sleep, alertness, hunger and much more. Chronobiology is the science of that timing.

A plant on a windowsill

The story often starts in Paris in 1729. The astronomer Jean-Jacques d'Ortous de Mairan noticed that a mimosa plant opened its leaves by day and closed them at night. He put it in a dark cupboard, expecting it to stop. It did not. The leaves kept opening and closing on roughly the same schedule, with no sunlight at all.

It was the first clue that living things carry their own internal clock, rather than simply reacting to day and night.

Naming the rhythm

For two centuries the idea developed slowly. In the 1950s the scientist Franz Halberg coined the word "circadian", from the Latin circa diem, meaning "about a day". The name captures something important: the internal clock does not run at exactly 24 hours. Left alone, it drifts. It needs a daily signal to keep it in step with the world, and the most powerful of those signals is light.

Finding the master clock

In the 1970s researchers began to find where the clock lives. In animals it was traced to a tiny cluster of cells deep in the brain, the suprachiasmatic nucleus, which sits just above where the nerves from the eyes cross. Our Chief Health Advisor, Dr Martin Moore-Ede, led the Harvard Medical School team that located it in the human brain. We tell that story in our article on the suprachiasmatic nucleus.

The position of that master clock explains why light matters so much. It takes its timing signal straight from the eyes.

A Nobel Prize for the clock's machinery

In 2017 the Nobel Prize in Physiology or Medicine was awarded to Jeffrey Hall, Michael Rosbash and Michael Young for discovering the molecular machinery of the clock. Working with fruit flies, they showed how a set of genes and proteins rise and fall in a loop that takes about a day to complete. The same basic design is found in humans.

One of the most striking findings is that the clock is not only in the brain. Almost every cell in the body keeps its own time. The master clock acts like a conductor, keeping the rest of the orchestra together.

Why it matters for health

When the body's clocks are in step, systems such as sleep, hormone release, body temperature and digestion each happen at the right time. When they fall out of step, through shift work, jet lag, or simply too little daylight and too much light at night, people tend to feel it. Researchers continue to study links between disrupted rhythms and wider health, and it remains an active field.

Chronobiology also explains why people differ. Each of us has a natural timing, or chronotype, and it changes through life.

Where light comes in

For most of human history the light we lived under came from the sun. It was bright by day and dark by night, and our clocks were built around that pattern. Today most of us spend the majority of our time indoors, under light designed to help us see rather than to keep our clocks in time. We explain why that matters in why light matters beyond seeing, and what can be done about it in our guide to circadian lighting.

At Sensio BioLabs, chronobiology is the science our work is built on. We are researching how indoor light can be designed around the body's timing, not just the room's appearance.

This article is for general information and is not medical advice.