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Daytime wounds heal much faster than those suffered at night

Surprising new research reveals that the time of day an injury is sustained affects the rate at which it will heal. Scientists have discovered that the body’s internal clock causes wounds such as cuts and burns to heal around twice as quickly if the injury happened during the day rather than at night.

The study, led by scientists from the Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge, is the first to show how the internal body clock regulates wound healing and optimizes conditions for daytime healing.

A person’s circadian rhythm controls nearly every cell in the body. Tests in both mice and skin cells showed that while the body’s internal clock is in daytime mode, wounds to the skin heal almost twice as efficiently as wounds suffered at night.

The research team also analyzed the records of 118 patients with burn injuries and found more evidence to support their findings. Using a database from all major burns units in England and Wales, the experts determined that burns sustained at night took an average of 60 percent longer to heal than burns that occurred during the day.

Daytime burns were classified as 95 percent healed after 17 days, while night-time burns took an average of 28 days to reach the same level of progress. The researchers determined that one reason for the accelerated daytime healing was that skin cells moved to the site of the wound to repair it much faster during those hours.

There was also more collagen present at the wound site in daytime hours, which continued for up to two weeks after the wound was inflicted. Human and mouse skin cells grown in a lab dish exhibited this same response, indicating that the process is not initiated by signals transmitted throughout the body but by the body’s natural circadian rhythm.

Dr. John O’Neill is the senior author on the paper from the MRC Laboratory of Molecular Biology.

“This is the first time that the circadian clock within individual skin cells has been shown to determine how effectively they respond to injuries,” said Dr. O’Neill. “We consistently see about a 2-fold difference in wound healing speed between the body clock’s day and night. It may be that our bodies have evolved to heal fastest during the day when injuries are more likely to occur.”

Lead author Dr. Ned Hoyle said, “Further research into the link between body clocks and wound healing may help us to develop drugs that prevent defective wound healing or even help us to improve surgery outcomes.”

The study is published in Science Translational Medicine.

By Chrissy Sexton, Staff Writer

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