Women really are the stronger sex. Female hormones suppress pain better than opioids, study finds
The battle of the sexes is centuries old, but a new study suggests women might have the upper hand when it comes to pain management.
Scientists from UC San Francisco have discovered the female hormones estrogen and progesterone can suppress pain by making cells that produce pain-relieving opioids.
This process helps block pain signals between the body and brain.
The researchers believe the discovery could help with developing new treatments for chronic pain resulting from diseases like arthritis and cancer.
They estimate it could 'change the lives of the nearly 20 percent of Americans who experience chronic pain that is not adequately treated.'
The US Pain Foundation reports more than 51 million American adults live with chronic pain and pain in America costs as much as $635 billion a year in direct health care costs, lost productivity, and disability payments.
The researchers say the findings could also explain why some painkillers work better for women than men and why postmenopausal women - who generally have significantly lower levels of female hormones - experience more pain.
The work, published in Science, reveals a breakthrough new role for immune cells called T regulatories (T-regs), which are white blood cells that regulate your immune system and are known for their ability to reduce inflammation.
The battle of the sexes is centuries old, but a new study suggests women might have the upper hand when it comes to pain management
Commenting on the findings, lead author Elora Midavaine said: 'The fact that there's a sex-dependent influence on these cells - driven by estrogen and progesterone - and that it's not related at all to any immune function is very unusual.'
The researchers looked at T-regs in the protective layers that encase the brain and spinal cord in mice.
Until now, scientists thought these tissues, called the meninges, only served to protect the central nervous system and eliminate waste.
'What we are showing now is that the immune system actually uses the meninges to communicate with distant neurons that detect sensation on the skin,' said Sakeen Kashem, an assistant professor of dermatology.
'This is something we hadn't known before.'
That communication begins when a neuron senses something that could cause pain. The neuron then sends a signal to the spinal cord.
The team found that the meninges surrounding the lower part of the spinal cord houses an abundance of T-regs.
To learn what their function was, the researchers knocked the cells out with a toxin.
The effect was striking - without the T-regs, female mice became more sensitive to pain, while male mice did not.
This sex-specific difference suggested that female mice rely more on T-regs to manage pain.
'It was both fascinating and puzzling,' said Kashem, who co-led the study with Dr Allan Basbaum. 'It actually made me skeptical initially.'
Further experiments revealed a relationship between T-regs and female hormones that no one had seen before: Estrogen and progesterone were prompting the cells to churn out enkephalin - a naturally occurring opioid.
Exactly how the hormones do this is a question the team hopes to answer in a future study.
But even without that understanding, the awareness of this sex-dependent pathway is likely to lead to much-needed new approaches for treating pain.
In the short run, it may help physicians choose medications that could be more effective for a patient depending on their sex.
Certain migraine treatments, for example, are known to work better on women than men.
This could be particularly helpful for women who have gone through menopause and no longer produce estrogen and progesterone, many of whom experience chronic pain.
The researchers have begun looking into the possibility of engineering T-regs to produce enkephalin on a constant basis in both men and women.
Basbaum said: 'If that approach is successful, it could really change the lives of the nearly 20 percent of Americans who experience chronic pain that is not adequately treated.'
