No one appears to know why, but the vast majority of chronic pain patients are women. Women suffer disproportionately from irritable bowel syndrome, fibromyalgia, headaches, osteoarthritis and many other conditions. Women also report more acute pain than men after the same common surgeries.
When researchers have asked male and female volunteers to subject themselves to experimental pain in a lab – women show lower pain thresholds and lower tolerance (they can’t tolerate intense pain as long).
But it’s only recently that researchers have begun to study the differences between the sexes. Most basic pain research is still done in male mice and rats.
McGill University pain geneticist Jeffrey Mogil has argued that men and women are so different in the way their nervous systems process pain that one day there may be ”pink pills for women and blue pills for men,”.
As more human research begins to address sex differences, there have been some fascinating results. Take hormones for example. Growing up, boys and girls show comparable patterns of pain until puberty, says Dr Navil Sethna, a pediatric anaesthesiologist at the Children’s Hospital Boston.
”After puberty, certain types of pain are more common in girls and, even if the incidence is the same, reported pain severity is more intense in girls than boys, especially for headaches and abdominal pain,” says Sethna. This pattern persists through adulthood; the lifetime prevalence for migraines is 18 per cent for women and 6 per cent for men.
Not all studies agree but many do show that, after puberty, women experience striking fluctuations in their response to pain at different points in the menstrual cycle. This has been noted in irritable bowel syndrome, headache and fibromyalgia. One explanation put forward by researchers is that oestrogen protects against pain at high levels and enhances it at low levels. (The male hormone testosterone seems to protect against pain.)
This theory fits with the observation that during pregnancy, when oestrogen levels are high, women often get fewer migraines. And it fits with the observation that, after childbirth, when oestrogen falls abruptly, the number of migraine attacks increases.
Dr Fernando Cervero, a pain researcher at McGill, suggests that it may not be the absolute level of oestrogen that matters, but the fluctuations in hormonal levels during the menstrual cycle. (Oestrogen levels climb in the first half of the cycle, then decline in the second half.) ”It’s the change that produces the change” in perceptions of pain, he argues.
What about a major hormonal change such as menopause (when oestrogen falls abruptly)? If low oestrogen really does result in more pain, women should experience more pain after menopause, but research results are inconclusive.
Several studies show that women who combat low levels of oestrogen by taking hormone replacement therapy end up having more back pain. Other studies detect no link between hormone replacement therapy and pain in older women and still others show that when women stop hormone replacement therapy, their pain appears to go up and they may get increased migraines.
One thing is clear: our culture encourages women to express pain and men to hide it. But this doesn’t mean that family, friends and doctors react sympathetically to women’s expression of pain. In the clinic, this often translates to gender bias and under-treatment of pain.
Women should not put up with any doctor who implies that they are needlessly whining. And neither should men tolerate doctors who don’t respect them or who trivialise their pain.
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