Cortisol Levels Linked to Brain Health: Insights from a Study on Aging

Reference: M. Geerlings et al. "Salivary cortisol, brain volumes, and cognition in community-dwelling elderly without dementia," Neurology, August 2015. 

As we age, our brains undergo various transformations, and understanding the factors that impact brain health becomes increasingly important. A recent study conducted by American doctors sheds light on one such factor — cortisol levels, the stress hormone, and their potential impact on brain health. 

The study, involving 4,244 individuals with an average age of 76 years who did not suffer from dementia, aimed to examine the association between cortisol levels, brain volume, and cognitive function. Participants underwent a comprehensive assessment that included brain scans to determine brain volume and various cognitive tests to evaluate thinking and memory. 

Notably, the researchers collected saliva samples from the participants in the morning and evening to measure their cortisol levels. Based on these cortisol measurements, the participants were categorized into three groups: those with high, medium, and low cortisol levels. 

The findings of this study revealed intriguing connections between cortisol levels and brain health. It was observed that individuals with high evening cortisol levels tended to have smaller brain volumes, which was particularly evident in their gray matter, with a difference of around 16 milliliters compared to those with lower cortisol levels. These same individuals also exhibited lower scores in cognitive tests assessing thinking and memory. 

In a paradoxical twist, participants with elevated morning cortisol levels demonstrated increased white matter volume in the brain (though not in the gray matter) and scored higher in certain cognitive tests, although not in memory-related assessments. This contrast highlights the importance of considering the timing of cortisol measurements. Evening cortisol levels are believed to represent the baseline cortisol level during periods of rest, while morning cortisol levels can be influenced by recent stress upon awakening. 

Depression has long been associated with an increased risk of developing dementia, but the exact mechanisms behind this connection remain a topic of active research. People suffering from depression often exhibit elevated cortisol levels, leading to the theory that this hormone may have a toxic impact on the hippocampus, a region of the brain critical for memory function. 

One of the study's authors, neurologist Lenore J. Launer, emphasizes that more research is needed to determine the causal relationship between cortisol levels and brain volume. "Since we have only observed the results of one analysis, we cannot say definitively what happens first — the increase in cortisol levels or the decrease in brain volume," notes Dr. Launer. "It is possible that a reduction in brain volume during aging diminishes its ability to resist the effects of cortisol, which, in turn, leads to further brain cell loss. By delving deeper into this relationship, we hope to find ways to reduce the negative impact of cortisol on the brain and cognition." 

This study adds another layer to the complex puzzle of brain health in later years and underscores the significance of addressing stress-related factors for overall cognitive well-being.