Regular exposure to stress can impact our physical and mental health, but how does it actually affect our brains? One new Harvard Medical School study answers that question.

Stress—especially when we experience it on a regular basis—takes a significant toll on our minds and bodies.

It can make us feel more irritable and constantly tired, and it impacts our ability to focus.

Chronic stress can also interfere with our sleep patterns, appetite, and libido, and it can also exacerbate a range of health conditions.

These include diabetes, heart disease, and gastrointestinal problems.

One study that Medical News Today covered earlier this year, in fact, saw that even minor levels of distress can increase a person's risk of chronic disease.

What impact does stress have on the brain in physiological and cognitive terms? Researchers from Harvard Medical School in Boston, MA, have explored this question and reported their answer in the journal Neurology.

The stress hormone affects memory

In their study, the researchers worked with participants with an average age of 49 and no diagnosis of dementia.

At baseline, the investigators asked each participant to undergo a psychological exam. They also assessed each participant's memory and thinking abilities. For the purpose of the study, they assessed these abilities again after an average period of 8 years.

Furthermore, at the beginning of the study, all the volunteers provided blood samples. The team collected them in the morning, after an appropriate fasting period, so that the blood test results would be accurate.

Specifically, the researchers were interested in measuring the participants' levels of blood cortisol, which is a hormone released chiefly in response to stress. After assessing cortisol levels, the investigators divided the participants into groups according to their results.

They categorized participants as having high, middle, or low levels of cortisol, where middle levels corresponded to the normal cortisol level range of 10.8–15.8 micrograms per deciliter.

The researchers found that people with high levels of blood cortisol had much poorer memory when compared with peers with normal cortisol levels. Importantly, impaired memory was present in these individuals even before obvious symptoms of memory loss set in.

These results remained consistent even after the investigators had adjusted for relevant modifying factors, such as age, sex, smoking habit, and body mass index (BMI).

"Cortisol affects many different functions," notes study author Dr. Justin B. Echouffo-Tcheugui, from Harvard Medical School, "so it is important to fully investigate how high levels of the hormone may affect the brain."

It is 'important to find ways to reduce stress'

Also, 2,018 participants agreed to undergo MRI scans, so that the researchers could measure their brain volumes. This allowed the researchers to confirm that people with high cortisol levels also tended to have lower total brain volumes.

Those in the high-cortisol group had an average total cerebral brain volume of 88.5% of total cranial volume vs 88.7% of total cranial volume in people with regular cortisol levels.

As for low cortisol levels, the researchers found no links at all between this and a person's memory or their brain volume.

"Our research detected memory loss and brain shrinkage in middle-aged people before symptoms started to show," says Dr. Echouffo-Tcheugui.

"[S]o it's important for people to find ways to reduce stress, such as getting enough sleep, engaging in moderate exercise, incorporating relaxation techniques into their daily lives, or asking their doctor about their cortisol levels and taking a cortisol-reducing medication if needed."

–Dr. Justin B. Echouffo-Tcheugui

"It's important for physicians to counsel all people with higher cortisol levels," he adds. Still, the researchers admit that their study does have some limitations—such as the fact that they only measured the participants' blood cortisol levels once, which may not be representative of their long-term exposure to this hormone.

Moreover, they note that most of the study participants were of European descent, which means that the findings may not accurately reflect the effects of stress on other populations.