People with higher levels of cortisol (a hormone linked to stress) in the blood performed worse on memory and other cognitive tasks and had smaller brain volumes than peers of the same age with average cortisol levels.

Blood serum cortisol, which varies in level throughout the day, was measured in the early morning (between 7:30 and 9 a.m.) in each fasting participant. The study featured a relatively young sample of male and female participants (mean age 48.5).

Memory loss and brain shrinkage were found in the study’s middle-age participants before the onset of any symptoms. People with higher cortisol levels may try to reduce stress by trying to get enough sleep and engaging in moderate exercise.