Why? Why? Why? Why? Why? Like any curious seven-year-old, asking why five times will often get you to the root cause of any problem, or so says the famous Toyota interrogative technique. Why do so many women suffer from chronic pelvic pain? Running down the chain of “whys,” we may find ourselves in an evolutionary conundrum. Why would we evolve to have chronic pain? Gynecologists Dr. Jarrell and Dr. Arendt-Nielsen dive into this evolutionary question in their new article in the August 2016 Gray Journal.
Let’s start with the very idea of using evolution to explain present-day problems. Evolutionary medicine was developed to give new insight into why our bodies behave the way they do, in the hopes that this insight might lead to better care and treatments. It’s important to remember that the theory of natural selection maximizes one goal: getting your genes into the next generation. It doesn’t necessarily maximize for strength or beauty or longevity, unless these things get you more offspring, who in turn reproduce more. Natural selection does not maximize health. It maximizes reproduction.
In our fast-paced modern world, the environment has changed faster than biological evolution. Some scientists, including the authors of the present article, believe that a mismatch between our evolution-molded bodies and our quickly-changing environment could explain chronic pain. Evolutionary medicine does not seek to explain the immediate “how” questions- the physiological processes that cause the pain. It focuses on the deeper “why.”
So, how do changes in our current environment explain chronic pelvic pain? The authors posit that women now have more menstrual cycles in their lifetimes than ever before, resulting in more chronic pelvic pain. The way I see it, this idea requires two things to be true. (1) Women actually do have more menstrual cycles than in the past. (2) More menstrual cycles lead to chronic pelvic pain.
A reasonable body of evidence supports the idea that women have more menstrual cycles now than ever in history. More menstrual cycles could result from earlier menarche, later menopause, less time spent pregnant or breastfeeding, and less amenorrhea. Historical literature supports the idea that the age of menarche has been dropping. In the 1860s, the average age of a girl’s first period was 17 years old. Now it’s 12 years old. When women reach menopause is not well established historically, likely because women did not live long enough to reach menopause. In 1860, the average woman died at 40 years of age. Our average age of menopause is 52 years. Thanks to birth control, women nowadays have significantly fewer pregnancies. In the 1800’s, the average woman gave birth to eight infants. Now our average family size is two children. Without formula, breastfeeding was (basically) the only option. Exclusive breastfeeding likely resulted in no periods for these women. Historically, women likely also experienced periods of amenorrhea due to miscarriages and periods of scarce nutritional intake. How have humans undergone so much change so quickly? Mostly, improved nutrition and healthcare.
Now on to our second question. Is there a plausible link between menstrual cycles and chronic pelvic pain? The theory of pain sensitization posits that visceral pain initiates the pain reflex causing referred pain and thus chronic pain. For pelvic pain, it goes something like this: normal pain from periods (dysmenorrhea) triggers the pain reflex, which becomes sensitized and hyper-responsive to any and all stimuli, even those that should not be painful. Researchers have found evidence of pain-sensing nerves becoming hyper-responsive to any stimuli after injury or inflammation. Hardcore scientists have even tracked down some suspect proteins. Scientists have demonstrated pain sensitization in women with chronic pelvic pain.
Women with pelvic pain are more likely to report a longer period of dysmenorrhea than women without the condition. The longer a woman experiences severe dysmenorrhea, the more sensitized to pain she becomes, and the higher her risk of chronic pelvic pain. Suppressing menstrual cycles has even been shown to reduce pain and sensitization.
Where do we go from here? The theory is, at the least, brain candy- something interesting to chew on. At best, it could provide a theoretical basis for menstrual cycle suppression to prevent or treat chronic pelvic pain. It also may cause you to question the idea that having a period every month for forty years is “natural” or anything close to what our ancestors experienced. Of course, all of this is theory. We can’t go back in time and test pain sensitization in ancient humans. We want to hear from you! Do you buy the evolutionary argument that more periods are causing the modern woman’s chronic pelvic pain?