About Your Mood  Mood & Seasonal Affective Disorder

Scientists Prove Light Treatments Fight Winter Blues

In the early 1980s, experts at the National Institute of Mental Health had a theory: If people get depressed when the days get darker, why not just give them more light? They tested this theory by building a 2-foot by 4-foot metal box with bright fluorescent bulbs inside and covered it with a plastic screen. A test subject was asked to sit in front of it for three hours before dawn and three hours after sunset every day. It worked.

In the 15 years since that day of discovery, further studies have shown the effectiveness of light therapy - using brighter lights and shorter treatment times - for patients with winter depression, known medically as seasonal affective disorder or SAD. An estimated 10 million Americans have SAD.

Why Winter Makes Us SAD

Think of winter depression as four months of jet lag. The human body has hundreds of 24-hour biological rhythms (called circadian rhythms), all controlled by one "internal clock." 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 is still dark. And that means that the sleep-wake circadian rhythm is out of step with the other rhythms, which we cannot 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.

One study supports that theory because it showed that morning light is more effective than evening light. Bright lights suppress the brain's secretion of melatonin. In other words, your hormones want you to stay sleeping, but the light convinces them that it is time to wake up.

For roughly 80 percent of SAD patients, melatonin levels peak just when it is time to wake up. For them, morning light therapy is best. For others, melatonin drops too soon, and they find themselves waking up in the middle of the night. For those patients, evening light therapy might work better.

Source: abcnews.com