Light therapy for winter depression

Content provided by the Faculty of the Harvard Medical School

Light therapy for winter depression

If you suffer from seasonal affective disorder, you don’t need to wait for longer days to get some relief.

Most of us welcome the sun’s effect on our mood, especially after a stretch of gray days. But for some people, reduced daylight during fall and winter months can bring on full-blown depression. For them, bright sunlight may represent more than a nice change in the weather: It can have therapeutic benefits. Exposure to the right kind of light, whether indoors or out, is the first-line therapy for alleviating the symptoms of seasonal affective disorder (SAD).

SAD is a form of depression that follows a seasonal pattern, almost always worsening during the darker winter months and returning every year at roughly the same time. It’s also known as “winter depression” or “winter blues.” Though there’s some evidence of a spring-summer pattern of depression, SAD is most commonly a fall-winter disorder.

This condition accounts for about 10% of all cases of major depression and occurs mostly in women. SAD makes you feel unhappy, anxious, tired, and irritable. It leaves you disinclined to socialize, and it undermines your ability to concentrate — all symptoms typical of depression. Many women increase their calorie intake (especially from carbohydrates) and sleep longer than at other times of the year. Interestingly, people with winter depression are often happy and productive the rest of the year.

SAD usually begins in a woman’s late teens or early 20s and often disappears after menopause. No one knows what causes winter blues, but there’s some evidence implicating melatonin, a hormone produced in the brain.

Body clocks out of kilter?

SAD appears to result from changes in the length of day, although more than lost sunlight may be involved. The disorder tends to last longer and be more severe at higher latitudes where there is a greater difference between the long days of summer and the short winter ones.

Many physiological functions are rhythmic — that is, they cycle in 24-hour intervals — including sleeping and waking, the release of certain hormones, and the highs and lows of body temperature. This circadian (24-hour) rhythm is essentially under the control of our genes, but it can adjust to environmental cues, notably changes in the light/dark cycle. Cells in the retina of the eye respond to the varying levels of light, signaling a pacemaker-like structure in the brain called the suprachiasmatic nucleus, which controls some of the body’s rhythms. One of the cycles this brain area regulates is the production of the hormone melatonin. Melatonin levels rise in the evening, helping to induce sleep, and fall in response to morning light.

According to one theory, the body clocks of people with SAD don’t adjust to winter’s later dawns and earlier sunsets. Melatonin thus remains elevated during their waking hours, dampening mood and energy. It’s also possible that people with SAD are hypersensitive to melatonin or overproduce the hormone in response to longer periods of darkness. Other evidence suggests that low levels of certain brain chemicals are involved.

The influence of light doesn’t completely explain SAD. No studies have demonstrated a causal link between a reduction in daylight hours and the development of the disorder. And various experiments have shown that some of the body’s cycles persist in the absence of light cues. Nonetheless, light therapy is uniquely (though not universally) effective in treating winter depression. For people with well-documented winter depression who aren’t suicidal and for whom antidepressants may not be an option, it’s usually the first treatment to be considered.

How light therapy works

The most common light therapy device is a box containing fluorescent lights mounted on a metal reflector. The light box is fitted with a plastic screen to filter out damaging ultraviolet frequencies. The screen also diffuses the emitted light, preventing glare. The important thing is the intensity, not the spectrum, of the light, so “full-spectrum” light isn’t necessary.

There are several light box models; some are designed to sit on a tabletop or desk, and others clamp onto a stand. They differ in size and portability — some are small enough to be packed in a travel bag — and they may be adjustable for height and light intensity. Light boxes work best when the user sits nearby at a prescribed distance and height, keeping her eyes open and looking ahead or slightly downward (see photograph). Looking directly at the box is not advisable.

Other light therapy devices include a battery-operated light visor worn on the head and the dawn simulator, a bedside light on a timer that gradually illuminates the bedroom in the morning to create an artificial early dawn.

Course of treatment. Using a standard measure of brightness, experts usually recommend about 10,000 lux, which is more or less equivalent to early morning sunlight. In the changing daylight of autumn, 15 minutes of 10,000-lux light once a day, right after waking, may suffice. Light exposure can gradually be increased to 30–45 minutes per session. Severe SAD may warrant longer exposure, perhaps in two sessions, up to about an hour and a half per day. If symptoms don’t improve in four to six weeks, light therapy should be re-evaluated and other measures considered.

Side effects. Light therapy has a few side effects — mainly headache, fatigue, irritability, and eyestrain. These usually subside with lowering the dose, that is, shorter sessions or increased distance from the light source. Sometimes a person with bipolar disorder develops mania as a result of light therapy. Anyone with photosensitive skin or a retinal condition, such as macular degeneration or a diabetes-related problem, is a poor candidate for light therapy.

Cost. The cost, in the range of $150–$300, is usually covered by insurance.

Other options

Treating depression begins with a diagnostic consultation. If it’s winter depression, light therapy may do the trick. But if not, antidepressant drugs, chiefly selective serotonin reuptake inhibitors such as fluoxetine (Prozac) and citalopram (Celexa) have been found effective for seasonal blues in controlled trials. In one study, giving citalopram following one week of light therapy helped sustain light-derived improvements in mood. People with seasonal mood changes may also benefit from psychotherapy, with or without light treatment.

For milder seasonal mood changes, adding more regular lamps to the home or workplace, sitting near windows, or spending more time outdoors may help. One study found that walking for an hour in the winter sunlight was as effective as 2 1/2 hours of artificial light. Snow helps: Its reflective surface intensifies the light.

Last updated:	August 21, 2006