The immune systems of men appear to be better equipped to shut down pain, which could explain why chronic pain is more common in women, research in mice and humans suggests.
Certain monocytes - a type of immune cell - produce an anti-inflammatory protein called interleukin-10 that "turns off" pain signals from nerve cells, study leader Geoffroy Laumet of Michigan State University reported in Science Immunology.
Production of these pain-relieving immune cells is driven by male sex hormones such as testosterone, the researchers found.
“The difference in pain between men and women has a biological basis. It’s not in your head, and you’re not soft. It’s in your immune system,” Laumet said in a statement.
In injured mice, higher numbers of IL-10-producing monocytes were seen in males than in females, and the males had faster resolution of pain after injury, the researchers reported.
Separately, among 245 humans recovering from injuries, resolution of pain was faster in men than in women and was associated with higher levels of monocytes and IL-10 in the men.
Giving testosterone pellets to injured female mice whose ovaries had been removed increased their IL-10 levels and sped up pain resolution.
In male mice whose testes had been removed, resulting in lower testosterone levels, IL-10 levels dropped and resolution of pain after injury was delayed.
Slower resolution of pain in women increases their risk of transitioning to chronic pain, the researchers noted.
The new findings shift "the thinking from how pain starts to why pain persists," they wrote.
The next step is to investigate how treatments could target this pathway and boost IL-10 production.
“This opens new avenues for non-opioid therapies aimed at preventing chronic pain before it's established,” Laumet said.
