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."
Sack points out that only a few generations ago, winter was a time of slowing down for everyone. After the harvest, farm families spent more time resting during the darker months, living off the fruits of their summer labors.
"It's only really in post-industrial society that people worked at the same rate in winter as the rest of the year," Sack says.
But few of us can solve the problem by retreating to an 1880s life style. And getting the sun to stick around longer on winter days seems even more unlikely.
The NIMH researcher came up with the next best thing, however: simulated sunlight, or phototherapy. They treated one group of winter depression sufferers with light measuring 2,500 lux in intensity, and used yellow lights of 300 lux--the same intensity as most normal indoor lighting--on a control group. "The problem consistently improved with the bright light, but not the dim," Sack says. Understandably so, he says. "If normal artificial light were bright enough to have a biological effect, nobody would get seasonal depression."
Sunlight, by comparison, measures about 30,000 lux on a bright day.
Researchers still aren't sure why phototherapy works, although their best speculation is that the increased light causes the pineal body, a glandular outgrowth from the brain, to secrete less of a hormone called melatonin, which is thought to work as a sort of tranquilizer to slow the body down.
At first, SAD patients were told to use the lights as long as five hours, glancing at them frequently but not staring at them. But now, with even higher intensity lights, they can get the same results with as little as half an hour of exposure a day.
Dr. Philip Wonder, who practices internal medicine in Diamond Bar and is also a SAD sufferer, uses a 10,000-lux light box for half an hour each morning. He finds that much more convenient than his old 2,500-lux light box, which took two to four hours daily for treatment.
"It was kind of a pain," he says. "My family hated it, it was ugly, and I had to drag it out every day." He also had trouble finding time in his schedule for light therapy, so he didn't use the lights consistently.
Lights for phototherapy are expensive--$300 to $500. Some insurance companies will cover the cost, but others haven't yet recognized them as legitimate medical devices.