Here in Boston, the last few autumns and winters have been unseasonably warm. Some of us worry about climate change and others simply enjoy the extra coat-free days. But, no matter what the temperature, it's still dark at 5:00 p.m. And that, to many of us, feels lousy.
For some of us, the lousy feeling is a sign of seasonal affective disorder or SAD. Significant mood changes occur that can't be dismissed with a shrug. The most common form of this disorder tends to start in the fall and gets worse in January and February. Relief comes with longer days in the spring.
About half a million Americans meet diagnostic criteria for SAD. Many more people have milder mood symptoms when the days get shorter. Symptoms may include loss of pleasure and energy, feelings of worthlessness, inability to concentrate, and an uncontrollable urge to eat sugar and high-carbohydrate foods.
As similar medications are used to treat seasonal affective disorder as other mood disorders, we'll focus here on light therapy, which is unique to SAD.
Bright white light therapy has been used to treat seasonal affective disorder since the mid-1980s. It involves sitting close to a fluorescent light box for 30 minutes, usually in the morning on waking. The light is much more intense than an ordinary light bulb. Proper light boxes provide 10,000 lux. (The "lux" is a measure of light intensity. By way of comparison, indoor light is about 100 lux, while a bright sunny day is 50,000 lux or more.)
Bright white light acts on cells in the retina that connect to the hypothalamus, a part of the brain that helps control circadian rhythms. These rhythms are thought to be disrupted in seasonal affective disorder.
Research shows that light therapy is as least as effective for treating seasonal affective disorder as is antidepressant therapy.
Although it is a mainstay of treatment, researchers have been looking for ways to improve and refine it because:
Researchers are looking at ways to improve the response or reduce the risk of side effects like mania or retinal damage.
Abnormal sleep rhythms are common in depression. The hormone melatonin, which helps regulate the cycle of waking and sleeping, may play a role in SAD.
The brain makes melatonin and usually produces more of it during the early evening. The timing of this surge varies from person to person. Some experts believe that, to optimize light therapy, it should be calibrated to a person’s nightly melatonin surge.
In this variation of light therapy, a preset light device turns on before a patient wakes up. Light intensity increases gradually from 0.001 lux (equivalent to starlight) to 250 or 300 lux (similar to sunrise) over a period of 90 minutes. Some small studies have found promising results with this technique.
Traditional devices use white light, a mixture of all the colors (such as blue, green and red) in the visible light spectrum. The use of light-emitting diode (LED) technology has made it possible to create smaller and more portable devices, and to test specific wavelengths of light.
Ganglion cells in the retina are particularly sensitive to blue light. This suggests that this wavelength may powerfully affect circadian rhythms. Researchers working in this area have begun to find evidence that lower intensity blue light (750 lux) is as effective as bright, full- spectrum light (10,000 lux). If this evidence holds up, it may be easier to provide this light through general lighting fixtures. It may also reduce the risk of side effects or discomfort.
Blue light may have its own special risks, since some wavelengths of blue light may cause retinal damage.
Experts recommend that patients with seasonal affective disorder first try traditional bright white light therapy after awakening. If it does not help or it creates bothersome side effects, it may be worth trying antidepressants or one of the alternatives under investigation. Since some people with SAD may be experiencing a variation of bipolar disorder, it's worth considering treatments for that disorder.
Although light treatment is relatively safe, there are a few cautions if you want to try it.
Michael Craig Miller, M.D. is editor-in-chief of the Harvard Mental Health Letter and an assistant professor of psychiatry at Harvard Medical School. Dr. Miller has an active clinical practice and has been on staff at Beth Israel Deaconess Medical Center for more than 25 years.