Relax: A new study shows that people with higher levels of the “stress hormone” tend to have smaller brains — but that doesn’t mean one causes the other.
The study, published today in the journal Neurology, reports smaller brain volumes and worse memories in people with higher-than-average levels of cortisol — popularly known as the stress hormone. But any media coverage that warns stress is going to shrink your brain is premature. “Right now all we can say is A is associated with B, we can’t really say anything about causality,” says Sudha Seshadri, a professor of neurology at the University of Texas Health Science Center at San Antonio and senior author on the study.
“The results are fascinating,” says Bruce McEwen, a neuroscientist at The Rockefeller University in New York who was not involved in the research. But, he adds, “Cortisol is tip of the iceberg. There’s a lot going on underneath.”
Cortisol is a hormone that the body pumps out in response to a number of different stressors — like sudden, psychological stress, or chronic inflammation. And this isn’t the first time scientists have linked the stuff to changes in the brain: other studies have connected excessively high levels of cortisol to shrunken brain regions, like the parts of the brain involved in memory. Shrinking brains could signal neurological or cognitive impairment. While it doesn’t necessarily mean that brain cells are dying, it could mean that those precious cells are losing their support systems, McEwen says. “It’s a sign that things are not good.”
In today’s study, a team of researchers led by Seshadri and Justin Echouffo-Tcheugui, an assistant professor at Johns Hopkins University, looked at the entire brain in more than 2,000 apparently healthy people. To find them, the research team turned to the Framingham Heart Study, a massive, three-generation study that’s been monitoring a community in Massachusetts since 1948. The researchers took blood samples from study participants to measure their cortisol levels, and tested their memory, reasoning, and attention. The researchers also imaged the study participants’ brains to look for differences in brain volumes as well as the white matter that insulates the brain’s biological wiring.
The participants fell into three different groups with cortisol levels at the low, medium, and high ends of normal. And the researchers found that the people with the highest cortisol levels tended to have poorer memories and attention, and smaller brain volumes — particularly women. The high cortisol group also showed signs of injury to their white matter, which the study authors speculated could contribute to the differences in memory, and attention: if you weaken the insulation, signals won’t travel along the wiring as efficiently.
Still, McEwen cautions readers against jumping to the conclusion that since cortisol is involved, stress is to blame. It’s true, surprising, stressful events can make your glands start squirting out cortisol. But other insults can do the same thing: the body uses cortisol to tamp down inflammation, for example. So chronic inflammation can also cause cortisol to rise. “It’s a cop out if you just dump this on the word stress,” McEwen says. (“When you read the paper, did you see something about stress?” study author Echouffo-Tcheugui asks. The answer is no — not until the reference section.)
It’s possible it’s the cortisol that’s triggering the changes in brain volume. That’s been seen before, McEwen says. But inflammation — if there is inflammation — could also be playing a part in the white matter injuries the researchers spotted. “Yes, it is possible, there could be a number of factors like that,” Seshadri agrees.
McEwen hopes that the team will continue to dig into why some people had higher cortisol levels than others, and what else might be affecting their brains — and the researchers hinted at plans to do so. “It’s a good step in the right direction,” McEwen says. “Underneath it there’s a lot of biology there that needs to be explored further.”