A study published on Wednesday in the journal Neurology showed stressed-out middle-aged people were more likely to show symptoms of memory loss.

The study revealed that middle-aged people with high levels of a hormone called cortisol in their blood have impaired memory when compared to those with average levels of the hormone.

Cortisol, produced by the adrenal glands, helps the body respond to stress and it can also help reduce inflammation, control blood sugar and blood pressure. High cortisol levels can be caused by stress, medical conditions or medications.

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

The researchers identified 2,231 people with an average age of 49 who were free of dementia.

At the beginning of the study, each participant had a psychological exam and assessments for memory and thinking skills. Their memory and thinking skills were tested again an average of eight years later.

Participants also provided a blood sample, taken in the morning after a period of fasting. Researchers measured cortisol levels in the blood and then divided participants into low, middle and high groups.

A total of 2,018 participants also had an MRI brain scan to measure brain volume, according to the study.

After adjusting for age, sex, smoking, and body mass index, researchers found that people with high levels of cortisol had lower scores on tests of memory and thinking skills than those with normal levels of cortisol.

Also, high cortisol was linked to lower total brain volume. Those with high cortisol had an average total cerebral brain volume of 88.5 percent of total cranial volume compared to 88.7 percent of total cranial volume in those with normal levels of cortisol.

But no links were found between low cortisol levels and memory or brain size.

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