Working at night may harm your liver: study

Frequent international travels or working at night may harm your liver by disrupting the natural sleep-wake cycle of the body, a new study suggests.

Researchers, including those from University of Geneva (UNIGE) in Switzerland, showed that the size of the liver increases by almost half before returning to its initial dimensions, according to the phases of activity and rest in mice.

This fluctuation disappears when the normal biological rhythm is reversed. The disruption of our circadian clock probably has important repercussions on our liver functions.Mammals have adapted to diurnal and nocturnal rhythms using a central clock located in the brain.

The latter, which is resettled every day by the light, synchronises the subordinate clocks present in most of our cells.In the liver, more than 350 genes involved in metabolism and detoxification are expressed in a circadian fashion, with a biological rhythm of 24 hours, researchers said.

"Many of them are also influenced by the rhythm of food intake and physical activity, and we wanted to understand how the liver adapts to these fluctuations," said Ueli Schibler, professor at the Department of Molecular Biology of the UNIGE.

The mice forage and feed at night, while the day is spent resting. "In rodents following a usual circadian rhythm, we observed that the liver gradually increases during the active phase to reach a peak of more than 40 per cent at the



end of the night and that it returns to its initial size during the day," said Flore Sinturel from UNIGE.

Researchers found that the number of ribosomes, the organelles responsible for producing the proteins required for the various functions of the liver, fluctuated together with the size of the cell. "The latter adapts the production and assembly of new ribosomes to ensure a peak of protein production during the night," Sinturel said.

The amplitude of the variations observed by the biologists depends on the cycles of feeding and fasting, as well as diurnal and nocturnal phases. The fluctuations disappear when the phases of feeding no longer correspond to the biological clock, which evolved in the course of hundreds of millions of years.

Many human subjects no longer live according to the rhythm of their circadian clock, due to night work hours, alternating schedules or frequent international travels.

A previous study determining the volume of the human liver during six hours using methods based on ultrasound, suggests that this organ also oscillates within us, researchers said.

If mechanisms similar to those found in mice exist in humans, which is likely to be the case, the deregulation of our biological rhythms would have a considerable influence on hepatic (liver) functions, researchers said. 

The study was published in the journal Cell.