Hunting the Cause of Winter Depression

Medically Reviewed by Gary D. Vogin, MD
From the WebMD Archives

Jan. 24, 2002 -- Were doctors in ancient Greece right when they said a patient's mood was related to a balance of body fluids or "humors"?

New research suggests at least they may have been on the right track: Modern scientists have found a substance in the blood really is linked to mood.

In the first study of its kind, Yale researchers have focused on people with seasonal affective disorder (SAD), a condition that afflicts one in 10 people in the Northern U.S., primarily women. Unlike other forms of depression, SAD appears when winter arrives. Those who suffer from SAD typically feel sluggish and weak and inexplicably crave carbohydrates.

The study finds that too little of one "humor" in the blood -- known today as the light-sensitive bile pigment called bilirubin -- may indeed be related to SAD.

People suffering from SAD have lower nighttime levels of bilirubin in their blood, writes lead author Dan A. Oren, MD, associate professor of psychiatry at Yale University School of Medicine. His study appears in the current Society of Biological Psychiatry journal.

This "may be a clue to understanding the causes and treatment of winter depression," Oren explains in a press release.

Nine patients -- all men and women who had suffered from SAD in the past -- were the focus of Oren's study. For two weeks, they slept overnight in a sleep laboratory that was brightly lit from 9 p.m. to 10:30 pm. Lights were then turned off from 11 p.m. to 7 a.m., while they slept. Blood samples were taken throughout the night via an intravenous catheter then were tested for bilirubin levels.

During the mornings, patients had a course of "light box daily light therapy," a standard treatment for SAD that consists of one hour under a bright light.

The results? At the end of two weeks, the treated patients had significantly higher bilirubin levels than before treatment. However, their bilirubin levels were still not as high as the seven untreated controls who did not suffer from SAD, says Oren. The treated patients also showed fewer depressive symptoms than before.

So what's going on here? Oren says he isn't sure, but he has some ideas.

Studies looking at treatments for SAD have focused on the effects of light on mood. Scientists know that in humans, light may play a central role in behavior, and that there are biological clocks within all forms of life.

A strong dose of light from a special light unit has been shown -- in studies -- to relieve the depressive symptoms. But it's been a mystery why light is effective. Oren's research provides the link between light's impact on the blood and its association with depression.

Bilirubin is the most abundant known circulating antioxidant and may protect neurological pathways that regulate moods, he says. Also, bilirubin is known to have a circadian rhythm; levels gradually increase in the blood during the night and decrease during the day.

His future studies will help determine whether low bilirubin causes SAD, whether it contributes to the vulnerability to depression, or if it is a marker for the disorder.