Seasonal depression is known by many names, including atypical depression, seasonal affective disorder (SAD), and the winter blues. For simplicity's sake, I will use the acronym SAD. SAD is much more common than was believed twenty years ago. Norman Rosenthal, a SAD researcher and expert form the National Institutes of Health, estimates that 35 million Americans suffers from winter depression and that as many as 10 million may have severe cases of the syndrome. Three times more women than men suffer from SAD, although no none is quite sure why. It is much more common in people living in the northern and southern latitudes than those living closer to the equator. For example, SAD affects 10,000 out of every 100,000 people in Minnesota, New York, and Washington State, but only 6 out of every 100,000 people in Florida, Arizona, and Louisiana.
Many of the symptoms of SAD are quite different from the symptoms of nonseasonal depression. People with nonseasonal depression tend to complain of a lack of appetite, insomnia, low self-esteem, and feelings of helplessness or hopelessness. SAD sufferers have a different litany of woes. They are troubled by sleepiness, low energy, social withdrawal, and increased appetite - especially for sweets and other carbohydrates.
If you stop to think about it, the symptoms of SAD sound a lot like those of hibernation. Hibernating animals stock up on food in the fall and then climb into a dark hole and sleep out the winter. It doesn't take too much imagination to reframe these behaviors as carbohydrate craving, fatigue, and social withdrawal.
In addition to the millions of people who have bona fide SAD, many more people have "subsyndromal" SAD, a milder version of the affliction. In fact, two recent studies suggest that the majority of the population, including children, feel somewhat blue in the fall and winter. I one of the studies, more than two thousand parents completed a questionnaire about the wintertime behavior of their children. Forty-eight percent of the parents said their children showed one or more signs of winter depression. The most common was "eats more," followed by "sleeps more," "seems irritable". "seems sad," and "withdraws from family and friends)".
What does SAD have to do with melatonin? There is some evidence that the hormone might be responsible for at least one symptom of SAD - increased sleepiness. In 1990, Thomas A. Wehr, a researcher at the National Institutes of Health, subjected eight healthy young men to lighting conditions that mimicked seasonal changes in day length. The men spent one week in summer lighting conditions - sixteen hours of light and eight hours of dark. Then for the next for weeks, the lights were turned off at six p.m., plunging the men into the depths of winter. During the long winter nights, they produced melatonin for an average of two hours longer. But they stayed in bed three hours longer, akin to minihibernation.
A man who has spent many years exploring the biological link between light, moods, and melatonin is Alfred A. Lewy. Lewy first became interested in seasonal depression in the late 1 970s while working at the National Institutes of Health. At the time, he had a sixty-three-year-old patient, an engineer, with pronounced mood swings. When depressed, the patient was withdrawn, self-critical, and anxious; he lost enthusiasm for his normal activities and dreaded going to work. When his depression lifted, he felt better than well - he was filled with energy and needed few hours of sleep.
His would appear to be a typical case of bipolar mood disorder or manic depression, except that the man's mood swings were precisely linked with the seasons. Each year he would begin to feel glum around mid-July. He would remain depressed for the next thirty weeks or so. January or February, as the day length began to increase, his depression would lift, and he would feel high spirited until midsummer. He had been to a number of psychiatrists who treated him with the standard medications, including antidepressants and lithium, but he could not tolerate their side effects. Besides, he was convinced there was a more fundamental cure for his mood swings, one that uncoupled the link between seasons and his sanity.
Fortunately for Lewy, this particular patient was not only an engineer but a bit of an obsessive-compulsive and had been keeping a detailed record of his mood swings for the previous fourteen years. The diary showed an unmistakable correlation between mood and time of year. Lewy hypothesized that exposing him to artificial bright light in the midst of one of his seasonal slumps might trick his body into thinking winter was over, causing his depression to lift spontaneously.
In December 1980, when the patient was mired in depression, Lewy put him on an intensive schedule of light therapy. Each day the man sat in front of a bright light (2,000 lux) for three hours in the early morning and three hours in the early evening, in effect transforming the bleak Washington, D.C., winter into spring. The man's depressive symptoms began to remit in just four days. By the tenth day he felt well.
Today tens of thousands of people have learned that the antidote to SAD is GLAD - good light of adequate duration. (You can blame researcher Charles P. Maurizi, M.D., for this new acronym.) The precise mechanism by which light therapy relieves winter depression, however, is much debated. Lewy's explanation is that people with seasonal depression have a "phase-delayed" melatonin rhythm, which means that they start producing melatonin later at night than most people. This throws their circadian rhythms out of whack, making them feel tired and depressed. Exposure to bright light in the morning hours advances the onset of melatonin production to a more normal schedule. A number of studies support Lewy's theory, showing that morning light is more effective than evening light in relieving symptoms of SAD.
An alternative explanation has to do with light's effect on serotonin, not melatonin. It is by raising serotonin levels, in this theory, that light relieves depressive symptoms; any effect on melatonin production is merely incidental. Proponents of this theory argue that bright light at any time of day has been shown to improve the mood of people with seasonal depression, casting doubts on the phase-delay theory.
It may be decades before we understand all the complexities of the intricate dance between serotonin and melatonin, but at this point most experts in the field agree that bright light is a safe and effective therapy for SAD. People who pass the dark days of winter slumped on the couch between trips to the refrigerator can get relief in as little as three days by increasing their exposure to light. Spending an extra hour out of doors, sitting in front of a specially designed light box, or wearing a new high-tech "light visor" may be all they need to defeat SAD. Meanwhile, Lewy and his colleagues at OHSU are investigating whether taking melatonin at a prescribed time of day can also take the blues out of winter.