An Israeli study on sleep patterns in mice could improve both the length and the quality of life for human beings.
The study found that the duration of a mouse’s circadian clock affects both his longevity and how much he eats and drinks. The circadian clock is a mechanism that regulates physiological and biochemical processes throughout the day, including eating, sleeping, digestion and growth, and coordinates them with the external day-night cycle.
The particular breed of mice studied was genetically engineered to have a circadian cycle of exactly 24 hours, whereas in humans, and also in most other animals and plants, the circadian cycle is slightly longer than 24 hours.
"In conditions of complete darkness, or under constant weak red light, we would wake up every day half an hour later than the previous day,” explained Dr. Roee Gutman of Tel Hai Academic College, who led the study.
The study found that the mice with the 24-hour circadian clock lived longer and ate less than wild mice of the same breed, whose circadian cycle isn’t exactly 24 hours. Gutman said the longevity of the transgenic mice could be attributed both to the fact that their circadian cycle was exactly 24 hours long and the fact that their circadian clock was very strong, enforcing a clear distinction between sleeping and waking hours. The latter factor enabled the mice to better coordinate their eating times with their periods of activity.
Previous experiments on mice proved that it is possible to alter the length of their circadian clock, mainly by manipulating genes. But diet, and particularly foods rich in fat, can also affect the length of the circadian cycle.
There is no proof yet that circadian cycles can be altered in human beings, Gutman acknowledged, but “it’s certainly possible to strengthen the clock and thereby achieve better synchronization between the internal clock and the environmental clock.”
The main environmental factors that strengthen the circadian clock are exposure to strong light at regular hours — the dominant factor — and eating at regular hours. “Exposure to strong, clear light, especially in the morning, and sleeping in complete darkness, with no television on and no night-light in the bedroom, combined with regular eating hours, will strengthen the internal clock,” Gutman said.
In contrast, working shifts where the hours are changed every few days weakens synchronization between the internal and external clocks, creating a kind of permanent jet lag. Many studies have shown that this raises the risk of obesity, diabetes and possibly even cancer. Eating at night also raises the risk of diabetes and obesity.
Gutman’s study was actually started 20 years by Prof. Ruth Miskin of the Weizmann Institute of Science, who was trying to find ways to cure eye diseases. By chance, Gutman said, the study also revealed that genetically engineered mice lived longer than the control group. Moreover, they ate less and weighed less. This prompted the researchers to shift the focus of their study to longevity and weight control.
Gutman joined the study six years ago. Initially, he demonstrated the link between longevity, weight control and the circadian clock in female mice. Over the past two years, he has found a similar correlation in male mice. His article on the subject recently appeared in the “Journals of Gerontology,” which is published by Oxford University Press.
Previous studies on mice have also shown a correlation between circadian cycles and health, he noted.
“We understand that maintaining a dominant circadian clock is a process that promotes health and increases longevity,” he concluded. “So it’s worth sticking to clear, permanent hours for waking and sleeping, and also for eating — the two most significant factors in synchronizing the clock.”
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