If you’re feeling under the weather this winter, you aren’t the only one. Seasonal affective disorder (SAD) is a type of depression associated with the change in seasons, starting in the late fall and continuing into the winter months. Scientists estimate that this disorder affects between 1.4 to 9.7 percent of the United States population, causing symptoms like moodiness, anxiety and a lack of energy.
“It’s kind of like having jet lag for five months,” says Dr. Alfred Lewy, who defined the disorder with his colleagues at Oregon Health & Science University in the 1980s.
When seasonal affective disorder was first identified, many scientists believed these symptoms were caused by insufficient sunlight exposure. Now, however, scientists believe SAD is caused by darkness, based on the phase-shift hypothesis.
This hypothesis explains that circadian rhythms, the biological processes that recur naturally on a twenty-four-hour cycle, become disrupted. During the winter, the later time of sunrise causes the body’s circadian rhythm to shift. Because people still wake up at the same time, their shifted circadian rhythms become out of sync with their sleep cycles.
Melatonin, a natural hormone that helps to regulate the body’s sleep-wake cycle, is normally produced in higher levels at night. Exposure to sunlight during the day suppresses production of melatonin. When people wake up to dark skies during the winter or stay up way after the sun sets, their bodies do not get sunlight at the correct time and their circadian rhythms become mismatched. Studies have shown that people whose melatonin productions begin too early or too late before they go to sleep have higher rates of seasonal affective disorder. The disruption of the body’s natural cycle is believed to cause the symptoms of depression, overeating and sluggishness.
Some scientists wonder if there is an evolutionary reason behind the symptoms of drowsiness and overeating. This unproven theory suggests that these symptoms could correlate to higher survival rates during the winter, similar to the biological reasons behind animal hibernation.
Taking a low dose of melatonin at the right time can reset the body’s internal clock to treat the symptoms of seasonal affective disorder. However, scientists are now finding a treatment that addresses the root of the problem.
Light therapy has proved to be highly effective in treating seasonal affective disorder. This involves sitting next to a light box for 30 minutes as it emits a broad spectrum of light. Scientists recommend a dose of light in the morning immediately after waking up to adjust the body’s circadian rhythm with the actual time spent awake.
Scientists are interested in exploring the link between circadian rhythm misalignment and other mental illnesses, such as depression and bipolar disorder. Although the connection is still uncertain, some researchers are experimenting by treating these disorders with light boxes instead of medication.
People living at high altitudes or under heavy cloud cover are more likely to experience SAD. But scientists can’t explain why, even though many people experience a disruption of their circadian rhythm, not everyone suffers from seasonal affective disorder. Women and young people are more likely to be affected by SAD.
“There has to be some other biological vulnerability,” says Lewy.
For those suffering from seasonal affective disorder, this new treatment may provide a light at the end of the tunnel for the dark winter months ahead.