Dose-response relationships of dietary quality with mortality stratified by dietary inflammation and their joint associations among cancer survivors: a population-based cohort study.

BACKGROUND: Current evidence suggests that both higher dietary quality and consumption of an anti-inflammatory diet are associated with lower mortality risk. However, the potential interaction between dietary quality and dietary inflammation in relation to mortality risk remains unclear. Therefore, this study aimed to examine the dose-response relationship between dietary quality and mortality across different levels of dietary inflammation, and their joint associations among cancer survivors. METHODS: We conducted a prospective cohort analysis among 2,746 cancer survivors in National Health and Nutrition Examination Survey (NHANES). Dietary quality and inflammation were assessed by Healthy Eating Index (HEI)-2020 and Dietary Inflammatory Index (DII) scores. Mortality outcomes were determined using National Death Index records as of December 31, 2019. Primary outcomes included all-cause, cancer, non-cancer and cardiovascular disease (CVD) mortality. Associations were examined using restricted cubic splines (RCS), stratified and joint analyses in Cox regressions. RESULTS: During a median 79 months of follow-up, 228 cancer and 435 non-cancer deaths were recorded, with CVD being the leading cause among non-cancer deaths. In the pro-inflammatory diet group, higher dietary quality was associated with lower risks of all-cause, cancer, and non-cancer mortality. Nonlinear associations were observed for all-cause and non-cancer mortality (p for nonlinearity < 0.05). Stratified analysis showed that in the pro-inflammatory diet group, higher HEI scores were associated with lower risks of all-cause (HR: 0.56, 95% CI: 0.42-0.73), cancer (HR: 0.58, 95% CI: 0.33-0.99), and non-cancer mortality (HR: 0.54, 95% CI: 0.37-0.80). Joint analyses indicated that cancer survivors with both a high HEI diet and anti-inflammatory diet had the lowest risks of all-cause, cancer, and non-cancer mortality. The above correlations remained significant after excluding participants who died within 24 months. CONCLUSIONS: Among cancer survivors consuming a pro-inflammatory diet, higher dietary quality was significantly associated with lower mortality risk. Nonlinear dose-response relationships were observed for all-cause and non-cancer mortality. Moreover, the combination of a high HEI diet and anti-inflammatory diet was associated with the lowest mortality risk.