Serum bilirubin levels and risk of colorectal cancer in Korean adults: results from the Korean Genome and Epidemiology Study-Health Examinee (KoGES-HEXA) Cohort Study

BACKGROUND: Current evidence on associations between circulating bilirubin and colorectal cancer (CRC) risk is inconsistent.

METHODS: In this prospective study, we investigated associations of pre-diagnostic circulating levels of total and indirect bilirubin with CRC risk in 78,467 Korean adults aged 40-78 years at recruitment, considering potential non-linearity and sex differences. Hazard ratios (HR) and 95% confidence intervals (CI) for associations with CRC risk were estimated with Cox proportional hazard regression.

RESULTS: During a median 7.9-year follow-up, 539 incident CRC cases were recorded. In multivariable-adjusted models, higher levels of total bilirubin were associated with a 26% (CI: 42% to 7%) lower risk of CRC among men and women combined, comparing the highest with the lowest tertile (P-linear trend = 0.003). A U-shaped association was observed in men, with the lowest risk at approximately 0.8 mg/dL (=13.7 μmol/L) of total bilirubin (P for non-linearity = 0.01). Although the association was largely null in women, there was no evidence for effect modification by sex (P-interaction = 0.73). Associations between indirect bilirubin and CRC risk were similar.

CONCLUSIONS: Higher circulating levels of total and indirect bilirubin were inversely associated with the risk of CRC among Korean adults. The associations were strongly inverse and U-shaped among men.