Plants, animals and even bacteria go through a daily 24-hour routine, known as a circadian rhythm. Jet lag is what happens when the body gets out of sync with its surroundings after crossing time zones. It has been known that there are variations in the immune system throughout the day. Researchers are now drilling down into the details.

The immune system needs to detect an infection before it can begin to fight it off. Researchers at Yale University School of Medicine were investigating one of the proteins involved in the detection process - Toll-like receptor nine (TLR9), which can spot DNA from bacteria and viruses. In experiments on mice, the scientists showed that the amount of TLR9 produced and the way it functioned was controlled by the body clock and varied through the day.

Immunising mice at the peak of TLR9 activity improved the immune response, the researchers said. They said humans with sepsis, blood poisoning, were known to be at a greater risk of death between 02:00 and 06:00. Prof Erol Fikrig, who conducted the study at Yale University, said they had found a “direct molecular link between circadian rhythms and the immune system,” which could have “important implications for the prevention and treatment of disease.”