Seeing the Light of Day

The good news is that treatments for seasonal depression -- primarily the use of bright light, and in some cases melatonin supplements, to reset the body's clock -- can be effective.

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For most people with SAD, the trick is to get bright light exposure first thing in the morning to simulate an earlier dawn and shift the body clock forward, said Alfred Lewy, a psychiatrist and chronobiologist at Oregon Health & Science University in Portland. For some people, taking 0.3 to 0.5 milligrams of melatonin in the midafternoon can also help, he added.

For the minority of SAD sufferers who are larks, light in the early evening can help. (Some larks may also benefit from melatonin in the morning, keeping in mind that even small doses can make some people sleepy.)

Diagnosing yourself as owl or lark can be tricky. Wake-up times are affected by much more than your natural clock (whether your sixth-grade daughter has to be fed before trudging off to school in the dark, for example), so your sleep schedule is not a surefire clue. Lewy suggests trying morning light first, but switching to the lark regimen if symptoms worsen.

Many kinds of lights are available for SAD treatment. Although some experts recommend those rich in the sky-blue wavelengths (the color that ganglion cells respond to), others warn that intense blue light can damage the eye. Most research indicates that 30 to 90 minutes' exposure to fluorescent "white" lighting of about 10,000 lux works fine, ideally with a plexiglass diffuser to filter ultraviolet rays and dissipate glare.

So effective is light as a mood improver that many psychiatrists now suspect that their understanding of depression has been backward: The disturbed sleep and withdrawal into darkened rooms so often seen in patients with depression, bipolar disorder and related problems may be not a symptom of those diseases but a cause. Reset the clock, and the depression lifts.

A 2005 review commissioned by the American Psychiatric Association concluded that daily exposure to bright light was about as effective as antidepressants against several forms of depression.

Recent studies have suggested that light therapy can also help patients with Alzheimer's disease. "They have these random sleep and rest and activity patterns throughout the day," said Mark Rea, director of the Lighting Research Center at Rensselaer Polytechnic Institute in Troy, N.Y. When Rea and colleagues gave Alzheimer's patients daily doses of blue light at about the intensity of a standard fluorescent bulb, the patients' ability to sleep through the night was significantly enhanced.

Blue light also looks promising for its ability to induce alertness, said Mariana Figueiro, a program director at the Rensselaer research center. She is testing the light on submariners, who have trouble remaining vigilant because their biological clocks don't get cued to dawn and dusk.

Of course, the fact that artificial lighting can reset people's clocks and boost alertness at night speaks to its potential to throw normal rhythms into disarray. As though it were not bad enough that lighting is a 24-7 feature of modern life, said Avery of the University of Washington, people spend evenings staring at their "Microsoft blue" computer monitors, then wonder why they can't fall asleep.

"We've deseasonalized ourselves," said Thomas Wehr, a psychiatrist at the National Institute of Mental Health in Bethesda. "We are living in an experiment that is finding out what happens if you expose humans to constant summer day lengths."

The perfect solution, as any camper knows, is to give up artificial light, an approach that quickly brings one into a cycle of long, restful nights and easy awakenings at dawn. More realistically, experts recommend avoiding bright lights after dusk and perhaps wearing yellow sunglasses at brightly lit evening events to filter out the blue light that might fool your ganglia into thinking it is morning.