Looking at the research in recent years, stress really isn’t the badge of honor that some people may believe—being stressed doesn’t mean we’re successful or important, it may just mean that we’re overextended and may reach a state of burnout sooner. A new study in the journal Neurology reinforces this reality in a powerful and elegant way: It finds that people with higher levels of the stress hormone cortisol have subtle reductions in brain volume. Perhaps more relevant, they also appear to have slight reductions in their performance on memory tests.
The study was carried out by researchers from Harvard Medical School; the National Heart, Lung, and Blood Institute; Boston University School of Medicine; the University of California, Davis, at Sacramento; and UT Health San Antonio.
The team looked at data from the well-known Framingham Heart Study, which has been following participants (and their offspring) since the 1940s. They focused on participants who were middle-aged (average age, 48), and healthy—none had any signs of cognitive decline. The participants’ cortisol levels were measured and correlated with their performance on tests of memory and cognition, as well as their brain volume via MRI.
It turned out that people who fell into the highest third of cortisol level had reduced volume in the frontal and occipital (back-most) lobes of the brain. They also showed changes to the white matter (the tracks of connections between neurons), which might signal poorer connectivity.
But the behavioral results are at least as important: People with higher cortisol levels also performed worse on memory tests, like copying a shape that was presented to them, or being asked to recall a story after a 20-minute break. The effect was stronger in women than in men, but it’s not clear if this is because women are more stressed or more susceptible to the effects of stress.
Because it’s possible to have brain changes without cognitive changes, the fact that these participants did show slight memory deficits may be telling. Earlier work has certainly suggested that chronically raised cortisol levels has a range of negative effects on everything from weight to sleep to thinking skills and even dementia risk.
“In our quest to understand cognitive aging, one of the factors attracting significant interest and concern is the increasing stress of modern life,” said study author Sudha Seshadri in a statement. “One of the things we know in animals is that stress can lead to cognitive decline. In this study, higher morning cortisol levels in a large sample of people were associated with worse brain structure and cognition.”
The current study didn’t look at cognitive decline or dementia, but presumably that might be a next step for the team.
And there are some limitations to keep in mind. One is that cortisol was only measured once, not over time. It’s also not clear whether the people with higher cortisol levels were actually more stressed out subjectively. Finally, it's possible that there’s a more complicated relationship going on here than just stress-leads-to-problems—it could be, for instance, that reverse causation is at play, where existing early cognitive changes might cause cortisol levels to rise in turn.
But given what we know about cortisol and the effects of chronic stress, the results make sense. A causal relationship certainly makes intuitive sense—being stressed out makes it harder to think efficiently, so it’s logical that chronic stress might make minute changes accrue into measurable ones.
The new study might serve as a good reminder to take stress seriously and not make the mistake of thinking that self-care is for wusses.
“The faster pace of life today probably means more stress, and when we are stressed, cortisol levels increase because that is our fight-or-flight response,” says Seshadri. “When we are afraid, when we are threatened in any way, our cortisol levels go up. This study adds to the prevailing wisdom that it’s never too early to be mindful of reducing stress.”