Cortisol
The main stress hormone. Useful in the morning and in emergencies, a problem when it never comes down.
Cortisol is released by glands above your kidneys. It rises in the hours before you wake, which helps get you going, and it rises when something threatens you, which frees up energy to deal with it. That's the design. Evidence: solid
Trouble starts when the threat never ends: money, a bad boss, a marriage going wrong. Cortisol stops coming down when it should, sleep gets shallow, the belly tends to store fat, the immune system misfires, and the part of the brain that keeps things in proportion works worse. Evidence: decent
Why it matters
You can't stop cortisol and you shouldn't want to. You can help it come down: sleep, movement, daylight, and one person who knows what's going on. Evidence: decent Most of this site is about that.