Today is the winter solstice, the day the sun makes its lowest--and shortest--arc across the sky. But the sun isn't the only thing that gets lower and lower this time of year: Some people do, too.
As the days get shorter and shorter each fall, these people slowly start losing energy. They sleep more, but the extra rest doesn't seem to stem their deepening depression. And neither does the increasing amount of food they crave. As the problem worsens, they begin to lose interest in sex and other activities. They socialize and exercise less.
The problem is called seasonal affective disorder, or SAD. First identified in the early 1980s by researchers at the National Institute of Mental Health, SAD became an officially recognized disorder only this year.
Psychiatrist Dr. David Sack was one of those original researchers, working with Dr. Norman Rosenthal at NIMH. Now medical director of Los Altos Hospital in Long Beach, Sack also has a private practice in Huntington Beach, where he treats patients with SAD as well those suffering from other mood disorders. Sack says that while as many as 10% to 20% of people are affected significantly by the shortening days, only a small minority have such severe symptoms that they seek treatment.
The disorder is also less prevalent in Southern California than in many other parts of the country, not only because our latitude keeps us closer to the sun in winter, but also because we have more clear days, Sack says. "Because of those two factors, we're actually getting more sunlight," he says.
Sunlight is important, Sack says, because "it is the primary regulator of the body's biological clock. Without the sun, we would run on all sorts of strange times." Experiments have shown that in an artificial environment where there is no externally controlled light, the body's internal clock seems to have a day of about 25 hours, Sack says. "Sunlight has to reset the body's clock every day."
The NIMH researchers discovered SAD while researching the effects of the body's biological clock on such things as mood, sleep cycles and energy levels, Sack says.
SAD is also sometimes described as a hibernation response, the human parallel to the process many animals go through this time of year.
"I don't know that it's hibernation, but in a natural environment, SAD conveys an adaptive advantage," Sack says. "If you gain weight, that makes your body more energy efficient, and immobility also decreases energy consumption. But in our culture, food is available year-round, and we have indoor heating, so we don't need to adapt."
