A compound in the blood, bilirubin, has been identified to reduce risk of lung cancer, chronic obstructive pulmonary disease and all-cause death, based on a study consisting of half a million adults.

Bilirubin (formerly referred to as hematoidin) is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases. It is responsible for the yellow color of bruises, urine (via its reduced breakdown product, urobilin), and the yellow discoloration in jaundice.

Bilirubin is created by the activity of biliverdin reductase on biliverdin, a green tetrapyrrolic bile pigment which is also a product of heme catabolism. Bilirubin, when oxidized, reverts to become biliverdin once again. This cycle, in addition to the demonstration of the potent antioxidant activity of bilirubin, has led to the hypothesis that bilirubin’s main physiologic role is as a cellular antioxidant.

The study’s authors write:

“Based on our findings, bilirubin levels within the normal range appear to capture information about patients that may reflect a combination of environmental and genetically determined susceptibility to respiratory diseases. Further research is needed to investigate causal associations between bilirubin levels and respiratory outcomes. A fuller understanding of these mechanisms may lead to the potential use of targeted clinical treatments that mildly suppress UGT1A1 [liver enzyme uridine diphosphate-glucuronosyltransferase 1] activity and moderately increase bilirubin levels.”

The study included 504,206 adults from a U.K. primary care research database (the Health Improvement Network) with levels of serum bilirubin recorded between January 1988 and December 2008.

After various analyses and adjustment for several important health indicators, the researchers found that moderately higher levels of bilirubin within the range considered normal were associated with reduced risk of respiratory disease and all-cause mortality.

Estimates for the incidence rate of lung cancer per 0.1-mg/dL increase in bilirubin level were an 8% decrease for men and an 11% decrease for women. The estimate for chronic obstructive pulmonary disease (COPD) in men per 0.1-mg/dL increase in bilirubin level was a 6% decrease and for mortality in men was a 3% decrease. The results for COPD and mortality in women were similar.

There are no normal levels of bilirubin as it is an excretion product, and levels found in the body reflect the balance between production and excretion. However, when bilirubin levels are high, a condition called jaundice occurs, and further testing is needed to determine the cause. Too much bilirubin may mean that too much is being produced (usually due to increased hemolysis) or that the liver is incapable of adequately removing bilirubin in a timely manner due to blockage of bile ducts, liver diseases such as cirrhosis, acute hepatitis, or inherited problems with bilirubin processing.

While there is no one specific thing, it is clear that excessive and long- term alcohol consumption can lead to cirrhosis and a permanently damaged liver. Avoiding alcohol and over-use/long-term use of drugs and eating a proper diet may help to sustain a healthy liver. Blockages due to duct stones, pancreatic cancer, or cysts may require surgery.

Source: Journal of the American Medical Association

Written by Sy Kraft, B.A.