A new study from Johns Hopkins suggests cumulative stress can have an outsize effect on womens' memories, pointing to a possible reason why women experience dementia and related illnesses at a much higher rate than men.
Researchers analyzed information from 909 Baltimore-based participants in a long-running National Institute of Mental Health study. In following the aging subjects, the study found that women seem to experience more memory loss potentially linked to stress than men do.
Scientists already know that almost twice as many women as men get Alzheimer's disease, the illness studied by study author Cynthia Munro, a psychiatry professor at Johns Hopkins University. What they don't know is why. "A lot of research in that area looks at sex hormones," she says. But she and her collaborators looked somewhere different—at the stress hormone cortisol. Previous studies have shown that while the amount of cortisol produced in response to stress tends to go up with age for everyone, the bodies of women in their 60s and early 70s can produce up to three times as much as those of men in the same cohort. Although this new research found that women's memories are disproportionately affected by everyday stressors, Munro notes that her research could potentially apply to any sex or gender, since the stress hormone cortisol affects everyone.
These participants were first recruited in the early 1980s, and by the time of the study’s last two check-ins, which took place between 1993-1996 and 2004-2005, they were in middle age. During the 1990s check-in, the participants studied were all about 47 years of age, which puts them all at nearly 60 years old during the final round.
During these final two check-ins, participants were asked if they had experienced any traumatic events (incidents on the order of rape or assault) in the previous year. They were also asked if they’d gone through any stressful life experiences (relatively routine things such as job loss, marriage, or divorce). Although both of these things are stressful, one is associated with the kind of trigger many people never experience, while the other—everyday stress—is something everyone experiences pretty much all of the time, to one degree or another.
The participants' memory skills were also measured, as they were asked to remember 20 words spoken aloud to them by testers. Between the third and fourth visits, the number of words that participants could remember dropped. (This is normal: research indicates that as people age, their memories decline in a variety of ways as their brains change.) The researchers then looked at whether stressful life experiences or traumatic events had any impact on those memory declines. For women, they found, stressful life experiences were correlated with higher rates of poor performance on the memory testing.
The sex-based differences aren’t huge, says Munro. But they point to a possible cause of cognitive decline in women, who suffer from Alzheimer’s and other dementia-type diseases at a much higher rate than men. Her team will continue following up with the study participants in hopes of learning more, as those small differences may start to add up over time.
These results come as no surprise to those who research stress using animal models, says Emory University psychiatry professor Shannon L. Gourley, who uses mice in her own studies. But this does represent a big departure from most existing research on our own species. Studies in humans tend to focus on incidents that can cause post-traumatic stress disorder, while this latest research is "directly comparing everyday stressors that we all might reasonably expect to experience in life, including things that might be quite welcome, like the birth of a child," Gourley says. "They find that these everyday stressors are actually having pretty negative consequences for cognitive function in women."
Rebecca Shansky, a Northeastern University psychologist who studies stress in female rats, was struck by this as well. “I think it really shows there’s a separation between acute trauma versus long-term stress that is really deserving of more attention,” Shansky says.
There's still a lot to figure out about the link between memory and stress and how it affects different groups, says Munro. But there's a lot of promise in this work, too: It suggests potential treatments for Alzheimer's and dementia, which are currently incurable diseases. The World Health Organization's latest guidelines on preventing dementia recommended general lifestyle improvements like increased exercise, balanced diets made up mostly of plant-based foods, and minimal alcohol consumption. Maybe stress reduction strategies could be another way to lower the risk of cognitive decline, allowing older adults to live fuller, more productive lives.
