They took the first sample as soon as they woke up. Waking times ranged from 5.22 to 10.37 am. Their cortisol levels remained high all day. Differences in the average number of hours asleep for the two groups could not account for this. The researchers hope to discover whether high cortisol levels caused the early birds to wake early, or whether their hormone levels were high because of their early start.
Chronic stress is associated with depression and suppressed immunity.