The clock in every cell

Your body does not have one clock. It has trillions of them.

Almost every cell carries a set of clock genes that switch each other on and off in a loop lasting about 24 hours. That loop tells the cell when to make certain proteins, when to repair DNA and when to rest.

When we measured gene activity across many tissues around the day, a large share of genes rose and fell with the hour. Your body at 8 in the morning is not the same body at 8 at night.