Seasonal affective disorder: bring on the light

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Assuming that the Mayan calendar mania was wrong and the world spins madly on, today marks the shortest daytime of the year in the northern hemisphere. In Boston, we get just nine hours of daylight; Barrow, Alaska doesn't get any. Although the winter solstice marks a seasonal turning point, with daylight getting incrementally longer from here until June 21, for people with seasonal affective disorder it's just another day of feeling lousy.

People with this condition lose steam when the days get shorter and the nights longer. Symptoms of seasonal affective disorder include loss of pleasure and energy, feelings of worthlessness, inability to concentrate, and uncontrollable urges to eat sugar and high-carbohydrate foods. Although they fade with the arrival of spring, seasonal affective disorder can leave you overweight, out of shape, and with strained relationships and employment woes.

We don't know exactly why seasonal affective disorder occurs. According to a review published in the current issue of American Family Physician, there are probably several different causes, including changes in the body's natural daily rhythms (circadian rhythms), in the eyes' sensitivity to light, and in how chemical messengers like serotonin function.

Some people find that taking an antidepressant medication helps. A unique approach is the use of light therapy.

The value of light

If lack of sunlight causes or contributes to seasonal affective disorder, then getting more light may reverse it. Bright light works by stimulating cells in the retina that connect to the hypothalamus, a part of the brain that helps control circadian rhythms. Activating the hypothalamus at a certain time every day can restore a normal circadian rhythm and thus banish seasonal symptoms.

Light therapy entails sitting close to a special "light box" for 30 minutes a day, usually as soon after waking up as possible. These boxes provide 10,000 lux ("lux" is a measure of light intensity). That's about 100 times brighter than usual indoor lighting; a bright sunny day is 50,000 lux or more. You need to have your eyes open, but don't look at the light. Many people use the time to read a newspaper, book, or magazine, or catch up on work.

Although light therapy is at least as effective as antidepressant medications for treating seasonal affective disorder, it doesn't work or isn't appropriate for everyone. Some people need more light, or brighter light. Others can't tolerate bright light—in people with bipolar disorder, for example, it can trigger hypomania or mania. And even though the risk of eye damage from bright light is low, anyone with diabetes (which can damage the retina) or pre-existing eye disease should check with a doctor before trying light therapy.

In efforts to make light therapy more effective, researchers are looking to improve it in various ways. One approach is creating light boxes that simulate dawn and sunrise, gradually increasing in intensity from darkness to 300 lux. Another involves using lower intensity blue light, which has a more powerful effect on the retina than white light.

Planning your approach

When I see a patient with seasonal affective disorder, I suggest he or she try 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 light therapy alternatives under investigation.

Although light treatment is relatively safe, here are a few cautions if you want to try it.

• Before investing your money—and time—on bright light therapy, work with a professional who is qualified to make a diagnosis. It's important to evaluate your individual situation, and to determine whether you really have seasonal affective disorder.
• Buyer beware—the FDA does not test, approve, or regulate light box devices.
• Before buying a light box, ask about the wavelengths of light it delivers (to avoid any that might be harmful, experts recommend fluorescent light without ultraviolet wavelengths).
• Another way to determine whether a product fits the intended purpose is to see if it is used in any hospitals, clinics, or reputable research facilities.

Finally, keep in mind that depression, as well as the symptoms of seasonal affective disorder, can have many causes and that there are many good ways to treat them. Review all your treatment options. Above all, establish a relationship with a professional who can help you periodically review your progress.

This article was adapted from one written for Harvard Health Publication's partnership with InteliHealth. Photo courtesy Alaska Northern Lights.