Dietary inflammatory index (DII) and risk of prostate cancer in a case–control study among Black and White US Veteran men

Background: We hypothesized a pro-inflammatory diet would be associated with higher prostate cancer (PC) risk. Methods: We prospectively recruited incident PC cases (n= 254) and controls (n= 328) at the Durham Veteran Affairs, from 2007 to 2018. From a self-completed 61-item Food Frequency Questionnaire, we calculated dietary inflammatory index (DII^®) scores with and without supplements. We examined the association between DII scores with and without supplements and overall PC risk using logistic regression and risk of low-grade PC (grade group 1) and high-grade PC (grade group 2–5) with multinomial logistic regression. Results: Cases were more likely to be Black (58 vs. 42%), had higher PSA (6.4 vs. 0.8 ng/ml), lower BMI (29.1 vs. 30.6 kg/m²) and were older (64 vs. 62 years) versus controls (all p< 0.01). Both black controls and cases had higher DII scores with and without supplements, though the DII scores with supplements in controls was not significant. On multivariable analysis, there were no associations between DII with or without supplements and overall PC risk (p-trend = 0.14, p-trend = 0.09, respectively) or low-grade PC (p-trend = 0.72, p-trend = 0.47, respectively). Higher DII scores with (p-trend = 0.04) and without supplements (p= 0.08) were associated with high-grade PC, though the association for DII without supplements was not significant. Conclusions: A pro-inflammatory diet was more common among Black men and associated with high-grade PC in our case–control study. The degree to which a pro-inflammatory diet contributes to PC race disparities warrants further study. If confirmed, studies should test whether a low-inflammatory diet can prevent high-grade PC, particularly among Black men.