The study, which was conducted by researchers at Washington University School of Medicine in St. Louis and published in the journal Brain, compared the brain activity of male and female rodents when they underwent massive amounts of stress. 

The researchers measured the levels of amyloid beta—a key Alzheimer’s protein1—in the brains of male and female mice every hour for 22 hours, beginning eight hours before the mice experienced stress. They first measured the levels of stress hormones in the blood and observed that both sexes experienced the same amount of stress. However, they found that their brains’ responses to stress varied significantly between the sexes, with the brains of male mice responding quite differently to the stressful situation than female mice.

Even though both the male and female mice found the experience equally stressful, in the females, levels of amyloid beta rose significantly within the first two hours of experiencing the stressful situation. Additionally, its levels remained elevated throughout the monitoring period. In the males, however, researchers observed mostly no change in amyloid beta levels (aside from the 20% of male mice who experienced a very weak, delayed rise in amyloid beta levels).

Essentially, this study pointed to key ways in which male and female brains process stress completely differently, with further research indicating that this difference is due to a cellular stress response pathway in brain cells. Female rodents possess neurons that take up the stress hormone that’s linked to increased amyloid beta levels, but male rodents don’t possess these neurons and therefore don’t take up the stress hormone.

While it’s unclear whether this fundamental difference exists—or is as prominent in—humans, the study indicates biological differences between males and females when it comes to stress.

“There’s a fundamental biological difference between males and females in how they respond to stress at the cellular level, in both mice and people,” John Cirrito, Ph.D., an author of the study and associate professor of neurology, said in a statement. “We don’t think that stress is the sole factor driving the sex difference in Alzheimer’s disease. There are many other differences between men and women—in hormones, lifestyle, [and] other diseases they have—that undoubtedly contribute in some way. But that stress is driving one aspect of this sex difference I think is very likely.”

While this is not the first study linking stress to Alzheimer’s disease2, it’s unique in that it attempts to find out why women are much more likely to be diagnosed with the disease than men. One shouldn’t discount biological differences in reaction to stress as a prominent factor.