Higher bilirubin levels among people with levels in the normal range reduced the risk of lung cancer, death and chronic obstructive pulmonary disease (COPD), new study findings suggest.

With every 0.1 mg/dL bilirubin increase, the rate of lung cancer dropped by 8% among men and 11% among women (P<.001), UK researchers wrote in the Feb.16 Journal of the American Medical Association.

These increases were also associated with a 6% decline in COPD and a 3% decline in death among both men and women (P<.001).

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“A fuller understanding of these mechanisms may lead to the potential use of targeted clinical treatments that mildly suppress UGT1A1 activity and moderately increase bilirubin levels,” Laura J. Horsefall, MSC, of the University College of London and colleagues wrote.

They examined data from 371 practices and 504,206 patients ages 20 and older in a cohort of patients from the Health Improvement Network, a UK based research database. All patients had median recorded bilirubin levels (0.64 mg/dL in men and 0.53 mg/dL in women), but none had hepatobiliary or hemolytic disease.

In the eight-year follow-up period there were a total of 1,341 incident cases of lung cancer (2.5 per 10,000 person year), 5,863 cases of COPD (11.9) and 23,103 (42.5) all-cause deaths.

The researchers found that the rate of lung cancer dropped from five to three per 10,000 person years among men in the lowest bilirubin decile vs. those in the fifth bilirubin decile. Similar declines were observed for COPD (19.5 to 14.4) and death (51.3 to 38.1).

“Further research is needed to investigate causal associations between bilirubin levels and respiratory outcomes,” the researchers wrote.