Association of systemic immune inflammatory index with all-cause and cause-specific mortality among individuals with type 2 diabetes

Background The evidence regarding the association between the systemic immune inflammatory index (SII) and mortality among individuals with diabetes is limited. This study aims to evaluate the associations between SII and all-cause and cause-specific mortality among individuals with diabetes.Methods The study included 8,668 participants with diabetes from the National Health and Nutrition Examination Survey (NHANES) 1999-2018 with follow-up until 31 December 2019. The calculation of SII in this study was performed using the following formula: the neutrophil-to-lymphocyte ratio multiplied by the platelet count (10<^>9 cells/mu L).Results The study documented 2,463 deaths over 68,542 person-years, including 853 deaths from CVD and 424 from cancer. An increase in SII was significantly associated with higher all-cause and CVD mortality risk after multivariate adjustment. For each standard deviation increment in natural log transformed SII (lnSII), all-cause mortality increased by 17%, and CVD mortality increased by 34% (both P < 0.001). Additionally, the association between SII and all-cause mortality was U-shaped, with the inflection point at 6.02. The association between SII and CVD mortality was non-linear and J-shaped, where the risk increased significantly when lnSII exceeded 6.22. Furthermore, the association between SII and CVD mortality was attenuated in female and hyperlipidemia patients.Conclusion In this study, we observed a significant positive association between the SII and both all-cause and CVD mortality in patients with diabetes. Additionally, it was discovered that this association exhibited a non-linear pattern. These findings suggest that maintaining SII within an optimal range may play a critical role in mitigating the risk of mortality.