Cortisol is the human body's natural stress reliever. It's a helpful hormone, but when cortisol levels rise too high too often, a new study has found that it can be detrimental to memory.

When we feel high levels of stress, the steroid cortisol is secreted by our adrenal glands, increasing blood sugar, suppressing the immune system, and improving metabolism.

The University of Iowa has published a study showing a link between cortisol and short-term memory loss in senior adults. According to the study, unusually high levels of cortisol can cause a gradual shrinkage of synapses in the prefrontal cortex, the area of the brain that stores short-term memories. Synapses are the brain's connections that allow us to store, process, and remember information. Eventually, excessive cortisol can even cause these synapses to disappear altogether.

The study was written by assistant professor of psychology Jason Radley and second-year psychology graduate student Rachel Anderson. They studied 21-month-old rats, comparing them with four-month-old rats; that's the rough equivalent of comparing humans who are 65 years old and 20 years old, respectively. Radley and Anderson separated the rats based on their hormone levels. (Rats have no cortisol, but rather a comparable hormone called corticosterone.) Next, the rats were placed in a maze specially designed to require use of the rats' short-term memory to reach a treat.

The findings showed memory declined across all of the groups, but the older rats with high corticosterone levels had the most difficulty reaching their treat.

The takeaway is that, potentially, short-term memory loss in humans could be slowed or stopped altogether by lowering levels of cortisol through treatment. Extended spikes in cortisol have, in the past, been linked to other health issues including weight gain, digestive problems, and high blood pressure. Cortisol has also been linked to degradation of other areas of the brain in elder adults. The University of Iowa study's findings may be preliminary, but they seem to suggest a connection between short-term memory loss and stress.

"Stress hormones are one mechanism that we believe leads to weathering of the brain," said Radley in a press release about the study's publication. Radley and Anderson are keen to point out that stress hormones are just one of many factors that can contribute to memory loss as we age. The paper was published in the Journal of Neuroscience.