Ask Dr. K: Light helps overcome seasonal affective disorder

Like other forms of depression, SAD produces sadness, lethargy and fatigue, loss of interest in people and activities, impaired concentration and irritability. SAD also leads to oversleeping and overeating. (Most other forms of depression produce insomnia and weight loss.)

Only one drug, bupropion (Wellbutrin), is approved for SAD. But selective serotonin reuptake inhibitors (SSRIs) and other antidepressants are also effective.

Another treatment, known as light therapy, is at least as effective for treating SAD as antidepressants. Light therapy involves sitting close to a fluorescent light box for 30 minutes each day. The light is much more intense than the light produced by 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. A bright sunny day is 50,000 lux or more.)

Bright white light acts on cells in the eye’s retina. The retina connects to a part of the brain that helps control circadian rhythms of sleep and wakefulness. Scientists believe these rhythms may become disrupted in SAD.

Light treatment is relatively safe and side effects are uncommon. Some people become irritable, develop headaches, or their eyes are bothered by the brightness of the light box. Reducing the time of each light box session, or sitting somewhat farther away from the box, can often correct that problem.

If light therapy is done in the later part of the day, it can cause insomnia in some people when they go to bed several hours later. The obvious way of dealing with this problem is moving light therapy to earlier in the day.

Some people with SAD have also suffered from bipolar disorder earlier in their lives. There is some evidence that light therapy may provoke recurrent attacks of bipolar disorder, particularly the manic (hyperactive) phase of the illness.

The U.S. Food and Drug Administration (FDA) does not test, approve or regulate light box devices. Before buying a light box, ask which wavelengths it emits, to avoid any that may be harmful. For example, blue light may be more effective for SAD than full-spectrum white light. Theoretically, certain wavelengths of blue light might damage the retina. However, I’m not aware of any evidence that this occurs with light box therapy.

Finally, a healthy lifestyle, including regular exercise, a good diet and a strong social network, is also likely to help you cope with SAD.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.