Repeated jet lag could raise the risk of obesity-related liver disease and liver cancer, researchers warn.
"Liver cancer is on the rise worldwide, and in human studies we have now seen that patients can progress from fatty liver disease to liver cancer without any middle steps such as cirrhosis," says lead author David Moore, professor at Baylor College of Medicine in the US.
The study revealed that chronically jet-lagged mice developed liver cancer in much the same way as that described for obese humans.
According to the researchers when people constantly travelled through different time zones, worked night shifts, or pushed themselves to stay awake at the regular sleep time, their central circadian clock in the brain became chronically disrupted.
"We think most people would be surprised to hear that chronic jet lag was sufficient to induce liver cancer," Moore added.
In the study, the researchers changed the times the lights were switched on and off during the night each week to understand the effects of chronic jet lag in normal mice who were fed a healthy diet.
By changing the times the lights were switched on and off during the night each week, the researchers modelled the effects of chronic jet lag in normal mice who were fed a healthy diet.
They found that the mice gained weight and fat, and went on to develop fatty liver disease, which, in some mice, led to chronic inflammation and eventually liver cancer.
The jet-lagged mice lost normal control of liver metabolism, which included not only the buildup of fat, but also increased production of bile acids, produced by the liver to help in the digestion of food.
Earlier studies had linked high bile acid levels to liver cancer, in both mice and humans. The study revealed that circadian clock disruption activated two nuclear receptors that helped regulate liver bile acid metabolism.
Jet lagged mice lacking a receptor called FXR, which kept bile acid level in the liver within a normal physiological range, had higher bile acid levels and also higher rate of liver cancer.