In 1995, hoping to improve my sleep, I decided to watch TV early in the morning, for reasons explained here. One Monday morning I watched tapes of Jay Leno and David Letterman that I’d made. Nothing happened. On Tuesday, however, I woke up and felt great: cheerful, eager and yet somehow calm. I had never felt so good so early in the morning. Monday had been a normal day, I had slept a normal length of time. The good feeling was puzzling. Then I remembered the TV I had watched. It had seemed so innocuous. The notion that 20 minutes of ordinary TV Monday morning could make me feel better Tuesday but not Monday seemed preposterous. Absurd. Couldn’t possibly be true.
Except for one thing. I had done something to improve my sleep. Plenty of research connected sleep and depression. That research made it more plausible that something done to improve sleep would improve mood. I went on to confirm the morning faces/mood linkage in many ways. The research connecting sleep and depression had been the first signs of a hidden mechanism (we need to see morning faces for our mood regulatory system to work properly) I consider very important.
Two new studies further connect sleep and depression. One of them found that people who sleep normal amounts of time are less influenced by genes associated with depression than those who sleep longer or shorter lengths of time. The other found that teenagers who sleep less than usual are at greater risk of depression.
The theories that psychiatrists have used to justify anti-depressants (e.g., “chemical imbalance”) do not explain the many connections between sleep and depression. Depression is associated with lots of bad things, unsurprisingly, but the association with bad sleep is especially strong. It is not easily explained away. You might think that if you are depressed you are more tired than usual and therefore sleep more/better than usual. The opposite is true. All this might have generated, among psychiatric researchers, a search for a better theory — an explanation of depression that can explain the sleep/depression connections — but it hasn’t.