To study the effect of constant, chronic jet lag on health risks, scientists at the Baylor College of Medicine in Texas turned to a furry and trusted animal model. They reported that mice exposed to disrupted light and dark cycles for close to 2 years showed a host of conditions, including liver cancer.
All animals have a built-in circadian rhythm – a biological cycle that responds to environmental stimuli. One of the most important cues that affect the circadian rhythm is daylight. Light stimulates the release of hormones and metabolites that makes us more alert and reactive, increasing our energy and muscle strength. By contrast, darkness stimulates hormones, such as melatonin, that makes us tired and sleepy. When this cycle is disrupted animals experience desynchronosis, otherwise known as jet lag. And this phenomenon is on the rise.
"Recent studies have shown that more than 80 percent of the population in the United States adopt a lifestyle that leads to chronic disruption in their sleep schedules," said Loning Fu, associate professor at Baylor College of Medicine and the study’s senior author.
Corresponding with the trend in sleep disruption is the rise of cancers, including liver cancer. "Liver cancer is on the rise worldwide, and in human studies we've now seen that patients can progress from fatty liver disease to liver cancer without any middle steps such as cirrhosis," said co-lead author David Moore.
Fu, Moore, and colleagues set out to definitively answer if a link existed between sleep disruption and liver cancer. Indeed, after exposing mice to an altered light/dark cycle for nearly 2 years, they found that sleep really does affect cancer health.
Mice on the “social jet lag” schedule, as the authors put it, had skin disorders and neurodegeneration not seen in the control mice. Furthermore, gene expression analysis revealed altered pathways involved with cholesterol and bile acid production. Not surprisingly, the social jet lag affected the expression of genes involved in the regulation of their circadian rhythm.
"To us, our results are consistent with what we already knew about these receptors, but they definitely show that chronic circadian disruption alone leads to malfunction of these receptors,” said Fu. "And thus, maintaining internal physiological homeostasis is really important for liver tumor suppression."
"This experiment allowed us to take several threads that were already there and put them together to come to this conclusion. We think most people would be surprised to hear that chronic jet lag was sufficient to induce liver cancer,” said Moore.
Additional source: MNT