Women who suffer from depression outnumber their male counterparts nearly two to one. They’re twice as likely to have generalized anxiety disorder, a panic disorder, or a specific phobia, too. But scientific research on these conditions and the stress that often exacerbates them has long revolved around men.
Historically, scientists have preferred male-only test animal populations, in part to avoid the complicated hormonal fluctuations and reproductive cycles of female lab animals (and, by association, the human women on the receiving end of medical treatment informed by these tests). Science News reports that, finally, psychologists and neuroscientists are investigating the differences in the way male and female lab-animal brains respond to stress, which could lead to a better understanding of the gender gap in depression and anxiety disorders, and how to treat them.
One study, led by Debra Bangasser of Temple University, found that differing levels of the sex hormones estrogen, progesterone, and testosterone can affect a neuropeptide called corticotropin-releasing factor (CRF), which controls the nervous system’s reaction to stress. A previous study had established that CRF affects the brains of male and female rodents differently; after a stressful event, females showed more CRF receptors on the surface of their brain cells than males did, which made females more responsive to future inundations of CRF. Some of the stressed-out males’ CRF receptors moved to the inner part of their nerve cells, making them better able to handle future stress.
When Bangasser and her team exposed rats to high doses of CRF, both males and females engaged in “anxiety-related grooming.” The effect was significantly more pronounced in female rats, particularly those with higher levels of estrogen and progesterone. “A heightened stress response may bring an evolutionary advantage,” writes Susan Gaidos. “An enhanced response to stress hormones could help females—most often caregivers for the young—remain alert and ready to take action in a stressful environment.”
Another study found that oxytocin, the much-hyped “hug hormone” that’s been the subject of several recent and ongoing trials for depression treatment, may contribute to more anxiety in female mice than male ones when produced in response to a stressful event. In the study, test mice were housed with an aggressive mouse on and off for three days. Even 10 weeks after their encounters with the aggressive mouse, female mice “froze in fear” when faced with a strange mouse. Male mice recovered after two weeks. After 10 weeks, studies of the mice’s brain tissue revealed both a greater number of oxytocin-producing neurons and heightened oxytocin production in female mice, but not male ones. These results complicate researchers’ understanding of oxytocin, which shows up in higher levels in women suffering from post-traumatic stress disorder. The hormone may be causing stress-induced behavior modifications, not helping to mitigate them, as some suspect.
Including female mice—and, later, female humans—in health studies like these is vital to future recommendations for drugs and treatments, too many of which have been tailored to male-bodied specifications like metabolic rates and hormone levels. More than two decades since federal legislation demanded that the National Institutes of Health include women in all the clinical trials it funds, the organization still doesn’t keep track of whether women are represented in research on specific diseases, nor whether individual research centers are recording the trials’ sex-specific results.
But chalking the mood-disorder gender gap up to neurons and hormones doesn’t tell the whole story. According to a new report from Columbia University, gender-based pay disparities put women at a higher risk for depression and anxiety. Using data from a 2001-2002 poll of 22,581 employed U.S. residents aged 30–65, researchers matched up 9,000 pairs of women and men with equal work experience and education. In pairs where the women made less money than the men, the women were four times as likely to suffer from anxiety and more than twice as likely to experience a major depressive episode. In pairs where the men made less money than the women, the odds of either suffering from anxiety or depression were nearly equivalent. Neurological goings-on might make women more susceptible to mood disorders, but structural discrimination gives them the perfect environment to take root.