Study: Disrupting sleep routine triggers cancer in mice

November 28, 2016 By Mary Frost Brooklyn Daily Eagle
Researchers track the movements of a sleeping person in 1947. AP photo
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Researchers have uncovered more bad news for people with irregular sleep schedules.

Disrupting a regular sleep routine is connected to higher risk of liver cancer in mice, say a team of researchers from institutions including Baylor College of Medicine, the USDA/ARS Children’s Nutrition Research Center at Baylor and Texas Children’s Hospital, the Dan L Duncan Comprehensive Cancer Center at Baylor and Florida State University. The results appear in Cancer Cell.

The findings are timely considering that disrupted sleep is becoming increasingly common in the U.S., especially among teens and working-age people. Liver cancer is also on the rise.

This research adds to previous studies showing that persistent disruption of circadian rhythm in night-shift workers is a common risk factor for obesity, metabolic disorders and cancer.

The circadian rhythm is generated by an internal clock tied to the 24-hour cycle of the Earth’s rotation around the sun.

“Recent studies have shown that most people in the United States adopt a lifestyle with prolonged disruption of their circadian rhythm,” co-senior author Dr. Loning Fu, associate professor of pediatrics and molecular and cellular biology at Baylor, said in a statement.

“We usually are sleep deprived on weekdays and oversleep on weekends and holidays. This shift in sleep pattern is called social jet lag,” he added. “The largest difference in shifting is among children and teenagers; people stop shifting after they retire.”

Social jet lag has been recognized as a factor in the increased prevalence of obesity and nonalcoholic fatty liver disease, according to the researchers. Nonalcoholic fatty liver disease is the accumulation of fat in the liver of people who drink little or no alcohol. It is predicted to become the leading cause of liver disease in the 21st century in the U.S.

In the studies, control normal mice were maintained in 12 hours light and 12 hours dark circadian cycles throughout their life. “Jet lagged” animals, however, were switched between two time zones (with eight hour shifts) throughout the week, similar to an executive traveling from the U.S. to Europe and back every three days.

This treatment induced weight gain, development of a fatty liver and accumulation of bile acid in the liver in normal mice although they were eating a healthy diet.

About 10 percent of male mice in the jet lag group developed liver cancer, while normal mice kept in stable circadian cycles did not develop cancer, the researchers report.

 


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