About half a million Americans meet diagnostic criteria for SAD. Many more people have milder mood symptoms. 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.
Standard Light Therapy
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.
Two reviews of studies on light therapy found that it was as effective at treating seasonal affective disorder as antidepressant therapy. In some cases it was more effective.
Although it is a mainstay of treatment, researchers have been looking for ways to improve and refine it because:
It doesn't work for everyone. Studies have reported that 50% to 80% of patients get complete relief from depressive symptoms after bright light therapy. But that still leaves many patients who don't find it helpful.
Successful treatment may depend on carefully individualized timing and dosing of light. The light dose depends on the strength of the light source, the patient's distance from the light, light wavelength and duration of exposure. The recommendation for 30 minutes of daily exposure to 10,000 lux is based on average response to white light; some patients may not need that much exposure to benefit. Other people, such as parents of toddlers, may not be able to sit in front of a device for 30 minutes each morning.
Some people don't tolerate bright light. The biggest psychological risk is that bright light therapy may trigger hypomania or mania in patients with bipolar disorder. Mood-stabilizing medications can be given to reduce that risk.
Bright light can cause retina damage, although it's rare. Some medications can increase the risk, including some antipsychotic medication, lithium, melatonin and St. John's wort. A few medical conditions can also increase risk: People with diabetes or pre-existing retina disease should discuss their conditions with their doctor before trying bright light therapy.
Enhancing Light Therapy
Researchers are looking at ways to improve the response or reduce the risk of side effects like mania or retinal damage. Here's how:
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.
Researchers from Columbia University reported that remission from SAD was twice as likely if light therapy was precisely calibrated to these fluctuations in melatonin levels. They found that 80% of patients achieved remission if light therapy began 71?2 to 91?2 hours after an evening melatonin surge, compared with 38% of patients whose light therapy began 91?2 to 11 hours after the surge.
Individual melatonin shifts may vary by as much as six hours, which partially explains the difference between early birds and night owls. Melatonin is hard to measure, but the nonprofit Center for Environmental Therapeutics offers a free online Morningness-Eveningness Questionnaire (MEQ) that may help gauge the timing of therapy.
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.