Objective To explore the association between the composite dietary antioxidant index (CDAI) and the risk of all-cause mortality in patients with diabetes based on the National Health and Nutrition Examination Survey (NHANES) database.

Methods The study data were obtained from the NHANES database from 1999 to 2018, and a total of 8 365 diabetic participants were included. The mortality outcome data were acquired by matching relevant NHANES data with records from the National Death Index (NDI) database. A weighted Cox proportional hazards regression model was used to analyze the association between CDAI and the risk of all-cause mortality in patients with diabetes. Kaplan-Meier survival curves were plotted, and the Log rank test was used to compare the differences in survival rates during follow-up among groups with different CDAI levels. A restricted cubic spline (RCS) model was employed to fit the non-linear relationship between CDAI and the risk of all-cause mortality, and a threshold effect analysis was further conducted.

Results The weighted Cox proportional hazards regression model analysis showed that CDAI was a protective factor for all-cause mortality in patients with diabetes (P < 0.01). After adjusting for covariates, CDAI remained independently associated with the risk of all-cause mortality in patients with diabetes (P < 0.01). The risk of all-cause mortality in patients in the highest tertile (Q₃ group) of CDAI was 0.79 times that of patients in the lowest tertile (Q₁ group). The Kaplan-Meier survival curves indicated that the survival rate of patients in the low-level CDAI group (Q₁ group, CDAI < -1.58) was lower than that of patients in the high-level CDAI group (Q₃ group, CDAI≥1.16), and the difference was statistically significant (Log rank P < 0.01). The RCS analysis revealed a non-linear relationship between CDAI and the risk of all-cause mortality in patients with diabetes (overall trend P < 0.01, non-linearity test P < 0.01). The threshold effect analysis showed that when CDAI < 4.349, CDAI was negatively correlated with the risk of all-cause mortality (HR=0.97, 95%CI, 0.95 to 0.99, P < 0.01); when CDAI≥4.349, there was no significant association between CDAI and the risk of all-cause mortality (HR=1.01, 95%CI, 0.99 to 1.03, P=0.34).

Conclusion There is a significant association between CDAI level and the risk of all-cause mortality in patients with diabetes, and a high level of CDAI is a protective factor for all-cause mortality in patients with diabetes.