Chronic Pain Lasts Longer For Women Than Men, But A New Study Might Find An Opioid-Free Solution

Just under one quarter of Americans have some form of chronic pain, but when you compare men and women, there are interesting differences. Conditions including arthritis, spine disorders, neuropathy, fibromyalgia, migraines, and more can cause long-term pain for anyone, but these conditions are more common in women. In 2023, 25.4% of women reported chronic pain, while 23.2% of men did. Combine the statistically significant increased prevalence of chronic pain in women with longer durations of pain and the historic and continued dismissal of women's pain in medical settings compared to men, and it is clear why determining the differences should to be researched. From a new treatment for back and neck pain that can replace spinal discs without surgery to the recent study looking into the immune cells that offer clues about why chronic pain lasts longer in women, research can help.

In a Michigan State University study, researchers specifically examined hormone-regulated immune cells called monocytes. These cells are part of pain resolution, an active process that differs based on a person's sex hormones, such as testosterone. According to the study, there is a subset of monocytes that releases molecules that deactivate the pain-causing neurons.

In males, researchers noticed higher levels of interleukin-10 (IL-10), a substance produced by monocytes in mice that signals neurons to stop pain. This seemed to be a result of the IL-10–producing monocytes in males being more active. When they blocked male sex hormones, they found that the IL-10–producing monocytes became less active. Overall, the research suggests that male sex hormones are linked to more active production of substances that contribute to faster pain resolution. 

The Michigan State University study used a sample of mice to see the effects of IL-10 on pain, finding that mice with less IL-10 had delayed pain resolution. The researchers were specifically looking at the monocytes inside inflamed skin. They also determined that female mice have less IL-10 than male mice. The researchers then manipulated the sex hormones of female mice to understand what the impact of sex hormones may be. In female mice given an ovariectomy and dihydrotestosterone, IL-10 levels were higher, supporting the idea that testosterone increases IL-10–producing monocytes. Furthermore, when they gave male mice an orchiectomy or treated the mice with flutamide, both of which reduce androgen, pain resolution was delayed. Finally, the researchers tested the effects of injecting resolvin D1, a substance that could elevate IL-10 monocyte levels, and found that the injections did indeed speed up pain resolution in mice. 

Of course, even though scientists have mapped an entire mouse brain with mesmerizing results, which can help us better understand rodent testing, it is important to find out how IL-10 works in humans, too. In human data collected from 245 trauma survivors in another study, researchers found that men's pain was resolved faster than women's pain and that higher levels of IL-10 were associated with even faster pain resolution in men. The human data showed that men's pain resolved quicker than women's pain, and that the men had higher monocyte and IL-10 levels in their plasma after experiencing trauma. However, they couldn't prove that the monocytes were producing IL-10 in humans. 

The study's results could eventually change how pain is relieved. Opioid therapy is a commonly prescribed treatment for those suffering from chronic pain. Opioids activate opioid receptors, an area of nerve cells, in the brain, which then block pain signals sent between a person's brain and body. While effective, they have some severe side effects that cause some people to stop use, and they can be addictive. Opioid use can also lead to abuse, dependence, overdose, and mortality. Given the risk factors, searching for a safer alternative for pain relief is an important task, and IL-10 research may open the door to alternative pain relief methods.

The Michigan State University study posits that by targeting the immune cells that produce the IL-10 that deactivates the neurons that signal pain, there may be a way to resolve pain without resorting to opioids. However, there is more research to be done. For example, researchers can try to determine what exactly stimulates IL-10 production and if there are differences between IL-10 local to an injury site compared to circulating the rest of the body. This type of information can help them discover whether clinical immune cell therapies for pain would actually be effective for pain resolution. Hopefully, the difference between men's and women's chronic pain can result in effective pain resolution for everyone with chronic pain that is less risky than relying on opioids. In the meantime, there are other ways to reduce opioid use while still dealing with pain. Check out how the future of pain relief may come from wearable tech.