@robjohn, is this article?
https://www.eurekalert.org/pub_releases/2017-04/dgi-pdw042517.php
It was also written about in Parkinson's News Today in 2017 https://parkinsonsnewstoday.com/2017/05/09/study-reports-stress-hormone-could-be-used-to-treat-parkinsons-disease/

I found a follow-up study (2019) “Endurance Exercise Reduces Cortisol in Parkinson’s Disease With Mild Cognitive Impairment,” https://parkinsonsnewstoday.com/2019/05/24/endurance-exercise-helps-manage-cortisol-levels-parkinsons-patients/

"Physical exercise is associated with a lower production of cortisol in healthy individuals, and there is evidence that it may also reduce the risk and rate of Parkinson’s progression."
"While other studies are needed to confirm if lowering cortisol with physical exercise works for delaying disease worsening, this data supports the further exploration of the role played by the hormone in non-motor symptoms of Parkinson’s."

It would seem that exercise is important as many members have written about here on Connect. What keeps you active, RobJohn?