You may have come across a circular chart online that divides the day into twelve two-hour slots, each linked with an organ: the lungs in the early morning, the stomach at breakfast time, the heart around midday. It usually goes by the name of the Chinese body clock, or organ clock.
It's a lovely piece of tradition, and it helps to be clear about what it is and what it isn't. The body clock is a traditional Chinese medicine idea, not a scientific finding. Modern science does study daily body rhythms, but that's a separate field with its own discoveries.
The twelve two-hour periods
In ancient China the day was divided into twelve periods, each named after one of the twelve "earthly branches". From the reign of the Han emperor Wu, in the second century BCE, the twelve earthly branches were used to name these twelve periods of the day.
The body clock tradition matches each period with one of the twelve organs and its channel (meridian). The version most commonly shared today runs like this:
- 11pm to 1am: gallbladder
- 1am to 3am: liver
- 3am to 5am: lungs
- 5am to 7am: large intestine
- 7am to 9am: stomach
- 9am to 11am: spleen
- 11am to 1pm: heart
- 1pm to 3pm: small intestine
- 3pm to 5pm: bladder
- 5pm to 7pm: kidneys
- 7pm to 9pm: pericardium
- 9pm to 11pm: triple burner (sometimes called the triple heater)
Where does it come from?
The idea that the body follows the rhythms of the day is very old. The Huangdi Neijing, the classic text of Chinese medicine, already links times of day with the organs. Its own groupings are broader than the modern chart, though. It ties the morning periods to the liver and gallbladder, midday to the heart and small intestine, sunset to the lungs and large intestine, and midnight to the kidneys and bladder, with the four periods in between given to the spleen and stomach.
Zhai Shuangqing of the Beijing University of Chinese Medicine has set out this older, element-based pairing, and it's quite different from the organ-by-organ sequence on the modern chart. So if you see the body clock presented as exactly what the ancients wrote, bear in mind that its history is longer and more layered than that.
What about circadian science?
This is where it matters not to mix things up. Circadian biology, the study of the body's roughly 24-hour rhythms, is a real and well-established science.
In 2017 the Nobel Prize in Physiology or Medicine went to Jeffrey Hall, Michael Rosbash and Michael Young for "discoveries of molecular mechanisms controlling the circadian rhythm". Working with fruit flies, Hall and Rosbash, and Young in a separate lab, isolated a gene called period in 1984. Hall and Rosbash went on to show that its protein builds up at night and breaks down during the day. The three laureates showed that genes like period work in a feedback loop that keeps a self-sustaining daily cycle, and similar mechanisms operate in humans.
That research tells us a great deal about sleep, hormones and daily rhythms. It doesn't confirm the organ times on the Chinese body clock. The two ideas share a theme, that the body changes through the day, but they come from different places and work in different ways. Enjoy the body clock as tradition, then, and look to circadian science for the evidence.
Using the clock as a prompt
Held lightly, the body clock can be a pleasant way of paying attention to your day. When do you feel most alert? When does your energy dip? Do you wake at the same time most nights? Noticing these patterns is interesting in itself. If you have ongoing problems with sleep or energy, though, it's best to talk to your GP.
If you'd like to explore the tradition in more detail, try my interactive Chinese body clock, which shows which organ the tradition links with the time right now.