Brazilian researchers found that people who go to sleep late at night are nearly 3 times more likely to experience depression symptoms than people who go to sleep early and wake up early.
The researchers speculated that there may be an optimal time to fall asleep and to wake up.
My guess is that this may be accurate since it is only a relatively short period of time that we’ve had electricity which has allowed us to stay up far later into the night than our ancestors who had no electricity.