Cortisol before bed predicted the night, and the night the next day
Across 15 days in 95 young adults, a higher cortisol reading before bed came before a shorter, less efficient night, and the shortest sleepers had a flatter curve the next day.
What the study found
Bad sleep and high cortisol each predicted the other
The loop runs in both directions. Across 15 days in 95 young adults, a higher cortisol reading before bed predicted a shorter, less efficient night's sleep, and those who slept shortest or worst on average had a flatter cortisol curve the following day.
The caveat · Healthy people averaging age 20
The authors describe the effects as small. Everyone measured was young and healthy, at an average age of 20, so this says nothing about older adults or about anyone with a sleep or stress disorder. And these are the same people watched over time rather than an experiment, so something else in their days could be driving both ends.