When our body clocks run late: does it make us depressed?

A sudden rush of newly-published research has given us much more understanding of what it means to be an “evening person” or “night owl”. An evening person feels more alert as evening arrives, may have trouble getting to sleep at a normal bedtime, and may have trouble getting up in the morning. The contrast is a “morning person” who wakes up early rather easily, is energetic in the morning, and becomes more fatigued as the day goes on, perhaps having trouble staying awake to read or to watch television before bedtime. Extreme morning-person hours seemed typical and healthy a century and more ago. Before artificial light became convenient, it seemed natural for people to fall asleep within a few hours after sunset and to arise about dawn, as their farm animals do (1). Today, people at either extreme of the morningness-eveningness spectrum may complain of sleep disorders and seek medical help.