Daytime Injuries Heal More Than Twice as Fast as Those Sustained at Night

New research shows that injuries sustained during the day heal more than twice as fast as ones sustained at night. While bad news for anyone who tends to get drunk and clumsy after hours, this is potentially great news for anyone who at some point down the road finds themselves in need of surgery.

"You can see by eye, when the cell is wounded only 8 hours apart from each other, in a different circadian phase, the [daytime] wounded ones take off, and the [nighttime] one drags," corresponding author John O'Neill of the MRC Laboratory of Molecular Biology told Science. "We were really astonished."

Researchers collaborating from different institutions in the United Kingdom first studied skin wounds in mice, observing that circadian regulation played a role in the pace at which they healed. They then looked at data from 118 burn patients logged in the International Burn Injury Database and found that wounds inflicted at night took an average of 28 days to heal, while those inflicted during the day needed only 17. A new paper detailing the research was published in the journal Science Translational Medicine.

The human body's internal clock is on a 24-hour cycle. When the body sustains a wound that needs closing, it relies on skin cells called fibroblasts, the "cellular protagonists of wound healing," as the authors put it in their paper. But like humans, themselves, fibroblasts are awake (so to speak) during the day, and inactive at night.

"It is like the 100m," O'Neill told the BBC. "The sprinter down on the blocks, poised and ready to go, is always going to beat the guy going from a standing start."

While the next step is still further study, it's possible that this discovery could improve healing after surgery, either through tailored scheduling of the surgery itself or through use of drugs like cortisol, a steroid which can override the internal clock and maybe jump-start recovery from surgeries taking place at night.

"Treatment of wounds costs the NHS around £5bn [a little over $6.5 billion], which is partly due to a lack of effective therapies targeting wound closure," John Blaikley, a clinician scientist at the University of Manchester, told the BBC. "By taking these [circadian factors] into account, not only could novel drug targets be identified, but also the effectiveness of established therapies might be increased through changing what time of day they are given."