Low Levels of Bile Pigment Linked to Depression

[Guest guest]

Low Levels of Bile Pigment Linked to Depression

February 04, 2002 02:35:35 PM PST, Reuters

By Anne Harding

NEW YORK (Reuters Health) - The Ancient Greeks believed that a person's dominant body fluid, or ``humor,'' determined his or her personality and character. A person in whom blood was strongest would be cheerful and optimistic, while one dominated by phlegm would be calm and sluggish.

Now Connecticut researchers have shown that one of these ''humors'' may indeed have something to do with our moods--in particular the tendency to become depressed in the winter, a condition known as seasonal affective disorder (SAD).

People with low levels of bilirubin, which Hippocrates called ``yellow bile,'' may be more likely to suffer from SAD, Dr. Dan Oren of the Yale School of Medicine and VA Connecticut Healthcare System and colleagues report in the latest issue of the journal Biological Psychiatry.

Bilirubin is an orange-yellow pigment found in the blood and bile, a liquid released by the liver that helps digest fat. Bilirubin levels in the body follow a circadian rhythm, gradually increasing at night and decreasing during the day.

Oren and his colleagues measured nighttime bilirubin levels in nine SAD patients and seven healthy volunteers.

The SAD patients had lower bilirubin levels than the healthy patients, the researchers found. And, after 2 weeks of daily light treatment--the standard method for lifting seasonal depression--the SAD patients' bilirubin levels increased, although they were still lower than those of the normal volunteers.

Nobody is sure what purpose bilirubin serves in the body, Oren noted in an interview with Reuters Health.

``The conventional wisdom of the 20th century was that bilirubin was a useless leftover waste product of evolution,'' Oren said. But, he added, ``nature uses energy to make bilirubin and it's very unlikely and very unsatisfying to think that it serves no physiological purpose.''

In plants, a green pigment called phytochrome absorbs light and transmits the signal throughout the organism, acting like a time sensor. It helps tell the plant the appropriate time to sprout, flower, and so on.

Oren hypothesizes that bilirubin might serve a similar purpose in humans. The pigment may be a phototransducer, meaning it absorbs light and then transmits a signal, perhaps somehow cueing and controlling the biological clock. Evidence for bilirubin's role as a phototransducer include the fact that it is light-sensitive, can cross the blood-brain barrier, and can slip into cells and their nuclei with ease.

Bilirubin is also a potent and very abundant circulating antioxidant, Oren and his colleagues note, and could help protect the brain by wiping out tissue-damaging free radicals. This is another way that low bilirubin levels might leave some people vulnerable to SAD, they suggest.

The next step in his research, Oren said, will be to measure patients' bilirubin levels for a full 24 hours, and study a larger group of people.

While his findings provide no new information on how to treat SAD, Oren noted, they do help substantiate the effectiveness of light therapy for people with the disorder. ''It provides evidence that this is not magic, it's not voodoo, it's a real physiological phenomenon.''

SOURCE: Biological Psychiatry 2002 January.