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FeedInto the Light
When summer ends, SAD sufferers prepare for the worst.
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For many of us, the end of summer can induce a minor case of the doldrums—call it the post-Labor Day blues. But as the days get shorter, an estimated half-million people in the U.S. experience seasonal affective disorder, a potentially debilitating illness with the symptom-appropriate acronym SAD. 
Overnight, it seems, SAD sufferers become withdrawn and/or depressed, their once-sharp minds succumbing to poor concentration and sluggish thinking. They hide their weight gain with clothes; they prefer sleep and sweets to sex.
Then spring arrives, with its longer days, and it’s back to feeling normal again. In some people—especially men—the process can resemble bipolar disorder or manic depression.
The sunlight SAD sufferers seem to crave can be symptomatic of the improper production of a chemical called melatonin, the hormone secreted by the pineal gland. The pineal gland works in harmony with another part of the brain called the hypothalamus, the switchboard for controlling a range of needs and behaviors, from appetite and sexual desire to mood and sleep patterns. Nerve pathways link the pea-sized pineal gland directly to the eye. When working properly, it regulates the cyclical production of melatonin day and night.
Once regarded with skepticism, SAD is now widely accepted. Every time the seasons change, it seems there’s another news story about it. There’s even a Seasonal Affective Disorder for Dummies book available. In scientific circles, SAD’s connection with light—or the lack of it—is one of the more creative leaps in recent memory. Yet it’s surprising how a light-tracking brain chemical like melatonin could ever be overlooked. The symptoms are usually so clear-cut, with an annual relapse occurring every fall or, in regions with more sunlight, as late as December.
Light therapy is the most effective treatment for those with seasonal affective disorder. “It works relatively quickly,” says George Brainard, a professor of neurology at Thomas Jefferson University and a leading authority on light’s impact on the body’s daily rhythms. “You see the benefits in a few days to a week.”
Up until the early 1980s, most melatonin research focused on the skin—the production of vitamin D, for instance. The turning point came with a series of studies involving artificial light and the eyes. The National Institutes of Health looked at blood samples taken from depressed people to gauge how melatonin levels increased when light decreased.
All practicing psychiatrists, NIH researchers already understood melatonin’s role in preparing the body for sleep. Through these artificial light studies, they determined that it was possible to manipulate nocturnal melatonin secretions typically found in the blood from 1 to 3 a.m.
As recently as 2001, NIH studies focused on how melatonin secretions differed in SAD patients—especially in the way their bodies seemed to go into a hibernation mode during the winter months, with levels higher than normal. Further research suggests that the spike in melatonin isn’t necessarily the product of a faulty pineal gland, but rather the result of mixed signals sent to the hypothalamus.
It’s no shock that the hypothalamus plays a crucial role in SAD research. Not only does it control a range of needs and behaviors, but it’s also tied to our internal clock, or circadian rhythms. Studies suggest that too much darkness can somehow skew a SAD sufferer’s internal clock. So when dawn comes, melatonin levels remain high and come down slowly as the day goes on.
NIH researchers were both the first to identify SAD as an illness and view it as a disorder that can be remedied with daily light therapy during the winter months. A former NIH researcher and the founding director of Jefferson’s light research program, Brainard has expanded his studies on SAD’s effects to include areas like stress-reduction and tumor growth.
