The saliva of healthy older people should be tested for the level of the stress hormone cortisol and this may help identify individuals who should be screened for problems with thinking skills.

The association between morning and evening salivary cortisol levels and regional brain volumes in older persons without dementia and the relationship with cognitive functioning to determine the potential clinical relevance of observed differences in brain volume has been investigated.

Scientists from the US National Institute on Aging (Bethesda, MD, USA) and their colleagues studied 4,244 persons without dementia whose mean age was 76 ± 5 years, and 58% were women. All enrollees had a brain magnetic resonance imaging (MRI) scan, and assessment of cognitive functioning. Saliva samples were taken from the participants once in the morning and in the evening to determine cortisol levels. Participants were divided into three groups based on cortisol levels of high, medium, and low.

Saliva samples were collected with the Salivette collection device (Sarstedt; Rommelsdorf, Germany). Salivary cortisol was analyzed with a Delfia time-resolved immunoassay with fluorescence detection (PerkinElmer; Waltham, MA, USA). The lower detection limit was 0.43 nmol/L for a 50-mL salivary sample. Morning or evening cortisol values of greater than 100 nmol/L were considered unreliable and excluded, but this was only 0.7% of morning samples and 0.5% of evening samples. Dementia ascertainment was a three-step protocol and a battery of six different cognitive tests was administered to all participants.

In the 4,244 participants, the mean morning cortisol level was 20 ±13.5 nmol/L and the median evening cortisol level was 2.3 nmol/L. People with the highest level of cortisol were more likely to have a smaller overall brain volume than those with lower levels of cortisol. Those with the highest level of cortisol also performed worse on the memory and thinking tests than those with low levels of the hormone. 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.

Lenore J. Launer, PhD, the senior author of the study said, “Since this study just looked at a snapshot in time, we don’t know which came first: the high levels of cortisol or the loss of brain volume. It’s possible that the loss of brain volume that can occur with aging leads to a lesser ability of the brain to stop the effects of cortisol, which in turn leads to further loss of brain cells. Understanding these relationships may help us develop strategies to reduce the effects of cortisol on the brain and thinking skills.” The study was published on August 19, 2015, in the journal Neurology.

Related Links:
US National Institute on Aging 
Sarstedt 
PerkinElmer