Lin Kooi Ong, PhD
Chronic stress has been shown to have detrimental effects on the brain structure and functions in pre-clinical studies. These negative effects are partially attributable to the hypothalamic-pituitary-adrenal axis dysregulation indexed by high cortisol levels. However, there are limited human studies in general population. In this study, Echouffo-Tcheugui et al. used data from the Framingham Heart Study, a large community-based study, to examine the association of early morning serum cortisol with cognitive performance including memory, abstract reasoning, visual perception, attention and executive function in a population of 2231 young and middle-aged adults (mean age 48.5 years) without dementia. Brain Magnetic Resonance Imaging (MRI) was performed on eligible 2018 individuals for volume of brain structures, and integrity of white matter and gray matter. Interestingly, the team observed higher levels of serum cortisol were significantly associated with lower total cerebral brain and occipital and frontal lobar gray matter volumes, as well as poorer cognitive performance in memory and visual perception, with the association being prominent in women. Further, the team identified that higher cortisol was associated with decreased integrity of the white matter tracts.
While this community-based study includes a large sample size, comprehensive cognitive test battery, and MRI markers, the authors noted that morning blood cortisol was assessed only once in each participant. Circulating cortisol is routinely assessed in blood, saliva and urine, each representative of short-term cortisol levels. However, these biological sources for cortisol measurement are limited by diurnal fluctuations and acute stressful situations. An elegant approach to overcome this issue is the analysis of hair cortisol as measurement of cumulative stress. Hair cortisol levels reflect long-term cortisol accumulation over several months prior to hair sampling (see Table for comparison between various biological sources).
It can seem like stress is an inevitable part of life, but chronic stress can have deleterious consequences on the brain. Understanding these effects and how to manage stress can help promote overall health.