Low levels of bile pigment linked to depression

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Low levels of bile pigment linked to depression

By Anne Harding

NEW YORK, Feb 04 (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.