By Pat Anson, PNN Editor

It’s no secret that women are far more likely than men to experience fibromyalgia, migraine, osteoarthritis and other chronic pain conditions. Why that is has been linked to everything from gender bias in healthcare to childhood trauma to women “catastrophizing” about their pain.  

A new study published by UK researchers in PLOS Genetics suggests that part of the reason is genetic differences between men and women.

In the largest genetic study of its kind, researchers at the University of Glasgow looked for genetic variants associated with chronic pain in over 209,000 women and 178,000 men who donated their medical and genetic data to the UK Biobank.

The researchers also investigated whether the activity of those genes was turned up or down in tissues commonly involved with chronic pain.

They found that 37 genes in men and 30 genes in women were active in the dorsal root ganglion, a cluster of nerves in the spinal cord that transmit pain signals from the body to the brain.

The findings support previous work by the same research team, which found that chronic pain originates to a large extent in the brain, and to a lesser degree in parts of the body where people “feel” pain. The study also suggests genetic differences between men and women may affect the immune system and how the two sexes respond to medication.

“Overall, our findings indicate the existence of potential sex differences in chronic pain at multiple levels… and the results support theories of strong nervous system and immune involvement in chronic pain in both sexes,” wrote lead author Keira Johnston of the University of Glasgow. "Our study highlights the importance of considering sex as a biological variable and showed subtle but interesting sex differences in the genetics of chronic pain."

Gender Bias

While genetic differences may partially explain why women are more likely to feel pain than men, gender biases may explain why they are treated differently, according to another study recently published in the Journal of Pain.

Researchers at the University of Miami found that when volunteers observed male and female patients expressing the same amount of pain, they had a tendency to view female patients' pain as less intense and more likely to benefit from psychotherapy.

The study consisted of two experiments in which adult volunteers were asked to view videos of men and women who suffered from shoulder pain. The videos came from a database of real patients experiencing different degrees of pain, and included their self-reported pain levels when moving their shoulders in a series of exercises.

The volunteer observers were asked to gauge the amount of pain they thought the patients in the videos experienced. They were also asked how much pain medication and psychotherapy they would prescribe to each patient, and which of the treatments they thought would be more effective.

The study found that female patients were perceived to be in less pain than the male patients — even when they reported and exhibited the same pain levels. Researchers believe those perceptions were partially explained by gender-based stereotypes.

"If the stereotype is to think women are more expressive than men, perhaps 'overly' expressive, then the tendency will be to discount women's pain behaviors," said co-author Elizabeth Losin, PhD, assistant professor of psychology at the University of Miami.

"The flip side of this stereotype is that men are perceived to be stoic, so when a man makes an intense pain facial expression, you think, 'Oh my, he must be dying!' The result of this gender stereotype about pain expression is that each unit of increased pain expression from a man is thought to represent a higher increase in his pain experience than that same increase in pain expression by a woman."

The volunteer observers were also more likely to choose psychotherapy as a treatment than pain medication for the female patients.

Interestingly, the gender of the observers did not influence pain estimation. Both men and women interpreted women's pain to be less intense.

"I think one critical piece of information that could be conveyed in medical curricula is that people, even those with medical training in other studies, have been found to have consistent demographic biases in how they assess the pain of male and female patients and that these biases impact treatment decisions," said Losin.

"Critically, our results demonstrate that these gender biases are not necessarily accurate. Women are not necessarily more expressive than men, and thus their pain expression should not be discounted."