Shedding Light on Moods

Do you feel down when winter darkness sets in, and elated when the summer sun returns? For 10 million Americans, these seasonal mood swings are severe enough to make life hard to bear. Another 25 million suffer a milder form of the "winter blues." Norman E. Rosenthal, M.D., clinical professor of psychiatry at Georgetown University and author of Winter Blues, explains why people develop seasonal affective disorder (SAD), and offers ways to beat the winter blahs.

Nancy K. Dess: What exactly is SAD?

Norman E. Rosenthal: It is a periodic pattern of depression that deepens in the winter and lifts in the spring.

Why is mood so sensitive to seasonal change?

Biological rhythms evolved over millions of years to fluctuate seasonally. Day length is a stable seasonal cue and controls biological changes in a host of species. For many animals, an entire biobehavioral cascade—courting, conception and gestation—is timed to ensure spring births. Winter changes often involve energy conservation. For example, many reindeer enter a state called "arctic resignation." They appear tame and won't run away, which helps them survive the cold. Similarly, many SAD symptoms can be seen as conserving—overeating, oversleeping and low sexual activity.

But surely SAD isn't a good thing?

No. Seasonal variations are adaptive in some circumstances, but not in humans, who must function at the same level all year.

Is it triggered by changes in weather?

SAD is more a condition of light deprivation than of season. For example, a man who lives in Washington, D.C., and gets winter depressions may get relief from moving to Florida or switching to an outdoor job. SAD can also be intensified by stress. I knew a nurse who had SAD symptoms every winter until she retired. Now she gets up whenever she wants and doesn't work long days. Presto! No winter depression.

Of course, there are easier solutions than moving or quitting your job. You've pioneered light therapy, for one. What is it?

Light therapy just entails bringing light to the patient. Typically, the patient sits in front of a light box—a metal frame with fluorescent lights and a diffusing screen—for an hour each morning. Up to 80 percent of SAD patients drastically improve after using the boxes.

How do you know that the light is really working? Could patients' hope be reducing their symptoms?

In my first study, my colleagues and I compared a bright light to a dimmer light control, and the brighter light was superior. More recent studies indicated the superiority of bright light over various controls. Now we are studying the mechanisms by which light works. SAD patients' pineal glands, which secrete a sleep-inducing hormone called melatonin in the absence of light, may be less responsive to light. More light exposure may increase their response. They also may have a serotonin dysfunction that light restores to normal.

Could light treat other illnesses?

Perhaps. Bulimia and premenstrual syndrome also may be alleviated by light therapy. It can also shift the daily rhythms of people with abnormal sleeping and waking cycles. The jury is still out on whether it is useful in treating nonseasonal depression.

What practical advice can you offer to SAD sufferers?

You can increase light exposure simply by painting your room with bright paints. Combine exercise, which can improve mood, with light by walking outside. Vacation in the winter and head south. Manage your stress levels. Psychotherapy and antidepressant medications can help. These treatments have few side effects, helping people with SAD take back the winter.