Most of us are aware that stress can increase risks for certain conditions, such as cardiovascular disease, impaired immune function and psychological disorders. But now, a study suggests a link between high levels of cortisol - a stress hormone - and short-term memory loss in older individuals.
The researchers, from the University of Iowa (UI), publish their findings in the Journal of Neuroscience.
They note that although short-term boosts in cortisol are important for our survival - by making us more alert in the moment - exceptionally high or extended spikes in the stress hormone can yield negative effects, such as digestion problems, anxiety, weight gain and high blood pressure.
Jason Radley, assistant professor in psychology at UI and study author, says:
"Stress hormones are one mechanism that we believe leads to weathering of the brain. Like a rock on the shoreline, after years and years it will eventually break down and disappear."
Though previous studies have shown cortisol produces similar effects in other regions of the brain, theirs is the first to assess how it affects the prefrontal cortex - the area of the brain linked to short-term memory.
To further investigate, Radley and his team studied 21-month-old rats, which is the rodent equivalent to 65-year-old humans. The researchers explain that short-term memory lapses related to cortisol start around this age in humans.
Older rats with high cortisol levels performed worst
The team then compared the aging rats to 4-month-old rats - the equivalent to a 20-year-old person. These groups were then further separated based on naturally high or naturally low levels of corticosterone, which is the hormone equivalent of cortisol in humans.
The researchers say their findings could yield treatments that decrease cortisol levels, thus slowing or preventing short-term memory decline in older adults.
Next, the team placed the rats in a T-shaped maze that required use of short-term memory; to receive a treat, the rats had to remember which direction they had turned at the top of the T either 30, 60 or 120 seconds previously, and then turn the opposite way each time.
Results showed that, although memory depreciated across all groups as the time the rats waited before running the maze again increased, the older rats with high corticosterone levels performed the worst.
In detail, the older rats with high stress hormone levels chose the correct direction only 58% of the time, compared with the older rats with low stress levels, who chose it 80% of the time.
Additionally, when the team examined tissue samples from the rats' prefrontal cortexes under a microscope, they discovered the rats who performed poorly had smaller and 20% fewer synapses, compared with all other groups.
The researchers explain that this indicates memory loss, as synapses are the connections in the brain that help us process, store and remember information. When they shrink and disappear due to repeated, long-term cortisol exposure, short-term memory likewise diminishes.
By comparison, the older rats with low corticosterone levels exhibited little memory loss and performed in the maze almost as well as the younger rats, who were not impacted by either low or high stress levels.
Potential for treatments that decrease cortisol
Radley says that although their findings are preliminary, they suggest the possibility that short-term memory decline in older adults could be slowed or prevented by treatments that decrease cortisol levels.
- It helps to eat healthy, well-balanced meals
- Exercise regularly
- Get plenty of rest
- Take a break if you feel stressed
- Talk to others about your stress
- Avoid drugs and alcohol.
This could include treating people with naturally high levels of cortisol or those who encounter recurring, long-term stress as a result of traumatic life events.
Speaking with Medical News Today, Radley told us he and his team "are excited that such a possibility is suggested based upon our findings."
Regarding further research into the topic, however, he and his team are "uncertain."
"Aging studies are expensive and time consuming," he said, "yet we are giving consideration to a next set of studies."
Additionally, the research team says it is important to remember that stress hormones are just one of many factors when it comes to mental decline and memory loss in aging.
Medical News Today recently reported on a study that suggested stress hormone receptors in taste buds could explain emotional eating.