Dietary Inflammatory Index and Risk of Colorectal Cancer in Japanese Men

Background/Objectives: Unhealthy lifestyles lead to chronic low-grade inflammation, increasing the risk of colorectal cancer. Few studies in East Asia have examined the association between the dietary inflammation potential and colorectal cancer incidence. Therefore, we aimed to investigate this association further in the Japanese population. Methods: This study included 38,807 men aged 45-74 years who participated in the Japan Public Health Center-based prospective study (JPHC Study). The energy-adjusted dietary inflammatory index (E-DII) was derived from a food frequency questionnaire. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression models. Differences in risk due to a combination of E-DII and lifestyle were examined using interaction term. Results: During 14 years of follow-up, 1415 colorectal cancer cases occurred. A tendency to increased colorectal cancer risk was observed with consumption of pro-inflammatory diets among Japanese men (adjusted HR [95% CI] for the highest quintile: 1.20 [0.99-1.46], p trend = 0.08), with a significantly increased risk of colon cancer (HR: 1.28 [1.01-1.63], p trend = 0.03). A possible interaction was observed with alcohol consumption (p = 0.07), which was statistically significant for proximal colon cancer (HR: 1.14 [1.05-1.25] in drinkers; p interaction = 0.01). No significant interactions with other lifestyle factors were found. Conclusions: Consumption of pro-inflammatory diets increases colorectal cancer risk among Japanese men; alcohol consumption further increases this risk for drinkers. These findings suggest that colorectal cancer may be prevented through dietary modification.