Pigment protects heart's arteries.

Too much bilirubin-a yellow pigment in the bloodstream with no known function-causes jaundice. However, a recent study hinted that a slight excess of bilirubin might protect against clogged arteries. Now, researchers have additional evidence regarding bilirubin and heart disease.

Paul N. Hopkins of the University of Utah School of Medicine in Salt Lake City and his team have been studying 120 men and 41 women who had signs of early heart disease. Hopkins' team had data from blood tests entered into their computer, including values for bilirubin.They looked to see if this pigment shielded the heart.

"I found, to my amazement, that [bilirubin] was incredibly protective," Hopkins says.

The team compared the people with heart disease to 155 men and women with no sign of heart problems. The researchers divided the study participants into fifths on the basis of their bilirubin test scores. Men and women in the top quintile for bilirubin showed an 80 percent reduction in risk of heart disease compared to those in the lowest fifth.

Men and women in the top fifth had between 17 and 16 micromoles of bilirubin per liter of blood, respectively-values that are high but still within the normal range. In contrast, people with jaundice would have bilirubin scores three times as high, Hopkins says. Men and women in the lowest fifth had average bilirubin values of 6.9 and 5.1, respectively, the team reports in the February Arteriosclerosis, Thrombosis and Vascular Biology.

If the results are confirmed, they suggest that people at the low end of the bilirubin spectrum face a higher-than-average risk of heart disease, Hopkins says. Bilirubin may prevent oxidation of LDL, or low-density lipoprotein, also known as bad cholesterol. Researchers believe that oxidized LDL promotes the formation of the fatty plaque that can choke off an artery and cause a heart attack. So far, nobody has looked at whether a person can increase bilirubin values.