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Waseda University researchers have revealed how stress can disrupt the body’s internal clock.

Mice are nocturnal animals and therefore sleep during the day and are active at night. Stress incurred in the morning does not impact the their internal clock. However, stress incurred in the afternoon-evening and late at night slows down and speeds up the internal clock. Stress incurred right before going to sleep disrupts the internal clock and appears to stop the liver’s internal clock.

Our bodies have internal clocks that help maintain equilibrium of our various physiological functions. Disruption of this cycle (circadian rhythm or biological rhythm) is said to increase the risk of obesity, diabetes and cancer. Prior to this research, it was known that stress hormones affect circadian rhythm, but not how.

In experiments using mice, researchers found that stress in the hours just before sleeping has a particularly large effect on biological rhythm, much more than in the early period after waking. Furthermore, they showed that stress can disrupt the functional rhythm of the brain and other organs even more than light, but also that the body can build up resistance to the effects.

These findings suggest that psychological stress magnifies the biological rhythm impacts of night-shift work, that negative impacts can be reduced by scheduling stressful activities early in the day, and that exercise can help build tolerance to stress.

The research team was led by Professor Shigenobu Shibata (Graduate School of Advanced Science and Engineering) and Assistant Professor Yu Tahara (Institute for Advanced Study), supported by funding from the Japan Society for the Promotion of Science and assistance from the Public Health Research Foundation.

Research results are published in the online science journal, “Scientific Reports,” by Britain’s Nature Publishing Group.

Entrainment of the mouse circadian clock by sub-acute physical and psychological stress