He found morning therapy at least twice as effective as evening therapy. It's less costly than antidepressant drugs, patients like it and the side effects are relatively mild. Now, researchers say, it's time to start testing light therapy on other conditions, like jet lag, premenstrual syndrome, nonseasonal depression and sleep disorders. Why Winter Makes Us SAD Think of winter depression as four months of jet lag. The sleep cycle is one rhythm.
Body temperature is another.
The brain's production of certain chemicals, like the nighttime hormone melatonin, is another. In the summer, we wake up with the sun and go to bed when it gets dark, so our body's internal clock is in synch with the sun. But in the winter, most of us force ourselves to wake up while it's still dark. And that means that the sleep-wake circadian rhythm is out of step with the other rhythms, which we can't control with an alarm clock. Scientists suspect that light therapy helps fight winter depression because it kicks the other biological rhythms, namely melatonin, into step with our artificially manipulated sleep cycle.