Wounds sustained at night heal twice as slowly, scientists find

Body clocks cause wounds such as cuts and burns sustained during the day to heal around 60 percent faster than those sustained at night, scientists have discovered in a finding that has implications for surgery and wound-healing medicines.

In a study published in the journal Science Translational Medicine on Wednesday, the scientists showed for the first time how our internal body clocks regulate wound healing by skin cells, and optimise healing during the day.

Burns that happened at night took an average of 60 percent longer to heal than burns that occurred during the day, the scientists found.

Night-time burns - sustained between 8pm to 8am - were 95 percent healed after an average of 28 days, compared with only 17 days if the burn happened between 8am and 8pm.

Body clocks – known as circadian rhythms – regulate almost every cell in the body, driving 24-hour cycles in many processes such as sleeping, hormone secretion and metabolism.

The key to accelerated daytime wound healing, the scientists found, was that skin cells moved more rapidly to repair the wound and there was also more collagen – the main structural protein in skin – deposited around the wound site.

 “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 John O‘Neill, who co-led the research at Britain’s Medical Research Council Laboratory of Molecular Biology.

 “We consistently see about a two-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.”

Treatment of wounds costs health services worldwide billions of dollars a year - in Britain’s National Health Service alone, the costs are estimated around 5 billion pounds ($6.56 billion) a year. Experts say this is partly due to a lack of effective drugs to speed up wound closure.

John Blaikley, a clinician scientist from Britain’s University of Manchester, said these new insights into the circadian factors important in skin repair should help the search for better wound-healing drugs. It could also help doctors improve outcomes by changing what time of day surgery is carried out, or when medicines are given, he said.