Mediation of associations between adiposity and colorectal cancer risk by inflammatory and metabolic biomarkers.

Inflammation and hyperinsulinemia may drive associations between adiposity and colorectal cancer (CRC) risk, but few studies have examined this hypothesis using mediation analysis. We used inverse odds ratio weighting and logistic regression to calculate odds ratios (OR) and 95% confidence intervals (CI) for estimated total effects (ORTE ) of body mass index, waist circumference, and adult weight gain on CRC risk, and estimated effects operating through seven inflammatory and metabolic biomarkers (natural indirect effect; ORNIE ) or through paths independent of these biomarkers (natural direct effect; ORNDE ) among 209 CRC cases and 382 matched controls nested within the Health Professionals Follow-up Study, a prospective cohort of male health professionals. A one-interquartile range (IQR) increase in body mass index (3.6 kg/m2 ) was associated with an ORTE of 1.40 (95% CI: 1.13, 1.73), which decomposed into an ORNIE of 1.26 (95% CI: 0.97, 1.52) and an ORNDE of 1.11 (0.87, 1.42), with possibly stronger mediation by these biomarkers for adult weight gain (IQR = 10.4 kg; ORTE = 1.32 [95% CI: 1.06, 1.64]; ORNIE = 1.47 [95% CI: 1.01, 1.81]; ORNDE = 0.89 [95% CI: 0.72, 1.11]), but no mediation for waist circumference. Mediation appeared to be stronger for the metabolic biomarkers than the inflammatory biomarkers. Inflammatory and metabolic mechanisms may mediate associations between both body mass index and adult weight gain with CRC risk.