Consistently high and irregular levels of the stress hormone cortisol are linked to faster cognitive decline in older adults.
Releasing the hormone cortisol is the human body’s natural way of responding to stress. Because cortisol can cross the blood-brain barrier and bind to receptors in regions responsible for cognition, researchers have long suspected that chronic stress takes a toll on brain function.
A newly published study in JAMA Network Open confirms this link, finding that irregular patterns and consistently high levels of cortisol in saliva are associated with cognitive decline later in life.
Tracking daily cortisol fluctuations over 11 years
The research tracked 3,895 individuals with an average age of 76.7 for up to an 11-year period. These participants were part of the Chicago Health and Aging Project and lived in four neighborhoods on the city’s South Side. To map daily hormone fluctuations, researchers measured cortisol from each person at three specific points over a 24-hour period, taking samples in the morning, afternoon, and evening.
Ted K.S. Ng, a translational gerontologist and neuroscientist at Rush and the study’s lead author, explained the focus on this particular diagnostic method.
“We tested salivary cortisol since it’s actively circulating in the body and interacting with organs, including the brain,” Ng said.
Racial differences in daily cortisol rhythms
The study cohort was notable for its demographic makeup, featuring 2,503 Black participants and 1,392 white participants.
“A strength of this study is that more than 60 percent of the study participants were Black older adults,” Ng said. “Many studies have been conducted primarily in White populations. This gives us an opportunity to examine differences in cortisol in saliva across racial groups while examining how cortisol patterns affect cognitive decline.”
The daily saliva samples revealed distinct biological rhythms between the two groups.
“The cortisol patterns differed between Black and white participants,” Ng said. “Black participants had lower overall levels, less change during the day, and a flatter pattern from morning to night. But even with these differences, cortisol patterns were linked to cognitive decline in similar ways in both groups. People with more variation during the day had slower cognitive decline, while those with the highest overall cortisol levels had faster decline.”
These results highlight the potential long-term effects of environmental pressures on cognitive health.
“The study design shows us that there are racial differences in cortisol patterns, which may reflect regular exposure to stress and its lasting impact on communities that face social and economic conditions,” Ng said.
A potential biomarker for general cognitive decline
While the elevated and flattened cortisol patterns tracked closely with general cognitive decline, the researchers noted that these biological markers did not predict which participants would specifically develop Alzheimer disease during the follow-up window. Still, monitoring how the body processes stress over the course of a day could eventually become a practical tool for preventative brain health.
“These findings suggest that this stress-related biomarker may one day identify people who may be at a higher risk for cognitive decline,” Ng said. “There are some disadvantages to studies that examine cortisol levels, so there would need to be more studies to examine what’s happening over a longer period of time in order to find new ways of supporting healthy cognitive aging.”
Reference: “Salivary Cortisol and Cognitive Decline and Alzheimer Disease in Older Adults” by Ted K. S. Ng, Todd Beck, Yashwanth Sudhini, Robert S. Wilson, Denis A. Evans and Kumar B. Rajan, , JAMA Network Open.
DOI: 10.1001/jamanetworkopen.2026.22955
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