Middle-aged people who have higher-than-average levels of cortisol — a hormone linked to stress — circulating in their bodies tend to perform worse on memory and other cognitive tasks than their peers with average levels of the hormone, according to a study published in the journal Neurology.

Higher levels of cortisol were also associated with less volume in certain areas of the brain.

Cortisol, which is manufactured by the adrenal glands, is often called “the stress hormone” because its production increases in response to stress. The new study therefore suggests — but does not prove — that higher levels of stress may, over time, injure the brain.

“In our quest to understand cognitive aging, one of the factors attracting significant interest and concern is the increasing stress of modern life,” said Dr. Sudha Seshadr, the study’s senior author and a neurologist at the University of Texas, in a released 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.”

Previous studies have linked high cortisol levels to negative effects on the human brain’s function and structure. Those studies have been criticized, however, for involving small numbers of mostly elderly adults and for not always excluding people with dementia and other confounding health conditions.

Study details

For the current study, Seshadr and her colleagues used data collected from 2,231 middle-aged participants in the ongoing Framingham Heart Study. All were healthy and had no signs of dementia. Their mean age was 48, and slightly more than half  (53 percent) were women.

The participants were given an initial series of tests to assess their memory and other cognitive (thinking) skills. About eight years later, they were asked to repeat the tests. During that second round of testing, the participants also had an early-morning (before breakfast) sample of their blood taken to measure their cortisol levels. In addition, most of the participants (2,018) underwent magnetic resonance imaging (MRI) to measure their brain volume.

The researchers stratified the participants into “high,” “middle” and “low” cortisol groups. The cortisol levels of the middle group (740 people) ranged from 10.8 to 15.8 µg/dL.

After adjusting for potential demographic and health factors that can affect cortisol levels, such as age, gender, smoking and body mass index (BMI), the researchers found that people in the high cortisol group performed more poorly on the cognitive tests, on average, than those in the other two groups. They also had — again, on average — lower brain volume.

The associations were particularly strong for women.

The researchers looked to see if people with APOE4, a genetic risk factor for heart disease and Alzheimer’s disease, might have higher-than-average cortisol levels. They found, however, that they did not.

Limitations and implications

This study is observational, so it doesn’t prove that stress damages the brain. The study also comes with other important caveats. Most notably, the cortisol measurements were taken just once, and therefore may not reflect the participants’ level of exposure to cortisol over time. Nor were they asked to quantify any stress they might have been under.

In addition, most of the participants were white, middle-class and suburban, so the results may not apply to other groups of people.

Still, plenty of other research has shown that high levels of ongoing stress can have a negative effect on health.

“The faster pace of life today probably means more stress, and when we are stressed, cortisol levels increase because that is our fight-of-flight response,” said 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,” she added.

How to reduce your stress

Here are some tips from the Centers for Disease Control and Prevention for coping with stress:

• Take care of yourself.
  • Eat healthy, well-balanced meals
  • Exercise on a regular basis
  • Get plenty of sleep
  • Give yourself a break if you feel stressed out
• Talk to others. Share your problems and how you are feeling and coping with a parent, friend, counselor, doctor, or pastor.
• Avoid drugs and alcohol. These may seem to help with the stress. But in the long run, they create additional problems and increase the stress you are already feeling.
• Take a break. If news events are causing your stress, take a break from listening or watching the news.

FMI: You’ll find the study’s abstract on Neurology’s website, but the full study is behind a paywall.