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 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.

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.

Investigators 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.

The conventional wisdom of the 20th century was that bilirubin was a useless leftover waste product of evolution. But 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.

Researchers hypothesize 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 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.

Biological Psychiatry January 2002

Dr. Mercola's Comments:

It never ceases to amaze me how many woman have their gallbladders removed every year. The same concept was used to perform lobotomies on seriously depressed patients not many years ago. Nearly all of the gallbladders that are removed are unnecessary. Of course most physicians wait beyond the point where recovery can occur, and the patient progresses to an acute surgical emergency that requires the gallbladder to be removed. But, if the patient is caught early and instructed on proper diet and exercise therapy, nearly all of these surgeries could be avoided. But to add insult to injury, virtually every surgeon tells the patient that his or her gallbladder really isn't necessary anyway and that there is no problem in removing it. Well, nothing could be further from the truth. The gallbladder stores bile and without bile, it is very difficult for your body to properly emulsify fats to absorb them. Trying to get fat into your body without a gallbladder is like trying to wash greasy dishes without soap. You can do it, but not very well. Now we find out from the above study that the gallbladder is also likely to be helpful in helping us treat depression. So, ladies keep your gallbladder if at all possible. Start on the eating plan and get your exercise program in place to avoid having your gallbladder removed. Related Articles: Gall Bladder Flushes and Cleanse Regular Exercise May Prevent Gallstone Surgery Diet, Exercise Tied to Gallstone Risk