Saliva cortisol associated with brain volume, cognitive function

Cortisol is closely linked to brain health through both its effects on the brain and its circadian regulation by the hippocampus, also the brain center for short-term memory. A study recently published in the journal Neurology shows that measurements of salivary cortisol can be an indicator for cognitive impairment and loss of brain volume.

"We investigated the associations of morning and evening salivary cortisol levels with regional brain volumes and cognitive functioning in community-dwelling older persons without dementia. "

The authors collected data for 4,244 subjects without dementia between 71 and 81 years of age who had a brain MRI  and assessment of cognitive function. To measure cortisol saliva was collected at home 45 minutes after awakening and again at night. These were used to observe the relationship among cortisol levels, brain volumes, and cognitive functioning.

Higher evening cortisol linked with cognitive impairment and loss of brain volume

Clinicians should recall that healthy adrenal regulation by the hippocampus displays a cortisol rhythm characterized by the highest level in the morning with a downward slope ending in the lowest level at night.

"Higher evening cortisol was associated with smaller total brain volume (highest vs lowest tertile −16.0 mL; 95% confidence interval −19.7 to −12.2 mL, adjusted for age, sex, education, intracranial volume, smoking, steroid use, white matter lesions, and brain infarcts on MRI). The smaller volumes were observed in all brain regions, but were significantly smaller in gray matter than in white matter regions. Poorer cognitive functioning across all domains was also associated with higher evening cortisol. Higher levels of morning cortisol were associated with slightly greater normal white matter volume and better processing speed and executive functioning, but not with gray matter volume or with memory performance."

Note also the positive indication of higher morning cortisol in reference to the cortisol circadian rhythm.

Clinical Note

The salivary cortisol circadian rhythm is easily measured in practice and a sensitive indicator for fundamental functions that must be well managed including inflammation,  glucose regulation, stress and brain function.The authors conclude:

"In older persons, evening and morning cortisol levels may be differentially associated with tissue volume in gray and white matter structures and cognitive function. Understanding these differential associations may aid in developing strategies to reduce the effects of hypothalamic-pituitary-adrenal axis dysfunction on late-life cognitive impairment."