A new study led by Cynthia Munro, an associate professor of psychiatry and behavioral sciences at the Johns Hopkins School of Medicine, has linked stressful life experiences among middle-aged women to greater memory decline in later life. The same trend was not found among men.
For their study, the researchers used data collected on a large group of Baltimore residents for the National Institute of Mental Health Epidemiologic Catchment Area study. That study recruited participants from 1981 to 1983 from five cities in the U.S. to determine the prevalence of psychiatric disorders. Participants met with researchers four times: during enrollment and again for interviews and checkups in 1982, between 1993 and 1996, and between 2003 and 2004.
During the third visit, participants were asked if they experienced a traumatic event in the past year, such as combat, rape, mugging, watching someone attacked or killed, receiving a threat, or living through a natural disaster. Roughly 22 percent of men and 23 percent of women reported experiencing one such event. They were also asked about stressful life experiences, such as marriage, divorce, death of a loved one, job loss, severe injury or sickness, a child moving out, retirement, or the birth of a child. About 47 percent of men and 50 percent of women reported having at least one stressful life experience in the year before their visit.
At the participants’ third and fourth visits, the researchers tested the participants using a standardized learning and memory test. The test included having participants recall 20 words spoken aloud by the testers immediately after they heard them, and again 20 minutes later. They were then asked to identify the words spoken to them among a written list of 40 words.
At the third visit, participants could recall on average eight words immediately and six words later, and correctly identified 15 words in the written list. By the fourth visit, participants recalled an average of seven words immediately, six words later, and correctly identified almost 14 words on the list. The researchers measured any differences in performance on the tests between the third and fourth visits, then compared those decreases with participants reports of stressful or traumatic events to see if there was an association.
The researchers found that having a greater number of stressful life events over the last year in midlife in women was linked to a greater decline in test performance. Women who experienced no stressful life event at the third visit remembered on average 0.5 fewer words at the fourth visit, compared to women with at least one stress life experience who recalled on average one fewer word at the fourth visit. The ability to recognize words on the written list decline by an average of 1.7 words for women with at least one stressor, compared to 1.2 words for women without stressors.
The same trend was not seen among women who had experienced traumatic events. The researchers believe this demonstrates that ongoing stress may have more of a negative impact on brain functioning than distinct traumatic events.
“A normal stress response causes a temporary increase in stress hormones like cortisol, and when it’s over, levels return to baseline and you recover. But with repeated stress, or with enhanced sensitivity to stress, your body mounts an increased and sustained hormone response that takes longer to recover,” says Dr. Munro. “We know if stress hormone levels increase and remain high, this isn’t good for the brain’s hippocampus — the seat of memory.”
The research team cautions that this study was designed to show associations among phenomena and not determine cause and effect. However, they believe that if future studies demonstrate that stress response does factor into the cause of dementia, then strategies designed to combat or moderate the body’s chemical reactions to stress may prevent or delay the onset of cognitive decline.
“We can’t get rid of stressors, but we might adjust the way we respond to stress and have a real effect on brain function as we age,” says Munro. “And although our study did not show the same association for men, it sheds further light on the effects of stress response on the brain with potential application to both men and women.”
Dr. Munro is a graduate of Ohio State University, where she majored in psychology. She holds a Ph.D. in clinical psychology from Kent State University in Ohio.
The full study, “Stressful Life Events and Cognitive Decline: Sex Differences in the Baltimore Epidemiologic Catchment Area Follow-Up Study,” was published in the International Journal of Geriatric Psychiatry. It may be accessed here.