Dietary Inflammatory Index (DII) and risk of colorectal cancer in Iowa Women’s Health Study

: Background: Colorectal cancer (CRC), the third most common cancer in the United States, has a natural history that usually encompasses several decades. Dietary components have been implicated in the etiology of CRC, perhaps through their effect on inflammation. Methods: We examined the ability of the dietary inflammatory index (DII) to predict CRC in the Iowa Women’s Health Study. The DII was computed based on dietary intake assessed by a 121-item food frequency questionnaire in this cohort of 34,703 women, aged 55–69 years, free of any self-reported prior malignancy at enrollment in 1986. Incident CRC cases were identified through linkage with the State Health Registry of Iowa (a Surveillance, Epidemiology and End Results program member). Cox proportional hazards regression was used to estimate hazard ratios (HR). Through the end of 2010, 1636 incident CRCs were identified, including 1329 colon and 325 rectal cancers. Results: Multivariable analysis, adjusting for BMI, smoking status, pack-years of smoking, hormone replacement therapy, education, diabetes and total energy intake, revealed positive associations between higher DII and CRC risk (HR for DII continuous : 1.07 per unit increase in DII (corresponding to 0.5 standard deviation unit increase); 95%CI 1.01- 1.13; HR for DII quintiles : Q5vsQ1=1.20; 95%CI 1.01- 1.43). HRs for DII were similar for colon cancer and rectal cancer, though not statistically significant for rectal cancer. Conclusions: These results indicate that a pro-inflammatory diet, as indicated by higher DII scores, was associated with higher risk of developing CRC. Impact : Pro-inflammatory diets are associated with increased risk of CRC.