Correlation matrix (n = 1172).

Dietary inflammation (DI) and suitable vitamin D intake was associated with frailty. However, the possible mechanism that how DI affected frailty was still unclear. The current study aimed to explore the mediating association of vitamin D levels in the link between DI and frailty. A cross-sectional study of 1172 participants from the National Health and Nutrition Examination Survey (NHANES) database in 2011−2014 was conducted. DI was assessed by the Dietary Inflammation Index (DII), serum vitamin D level were assessed by serum 25-hydroxyvitamin D3 (25-(OH)D3), and frailty was assessed by 49-frailty index. The mediation package in R 4.3.3 was used to examine the mediating association of serum 25-(OH)D3 levels on the relationship between DII and frailty. The prevalence of frailty was 32.3%. DII was negatively correlated with 25-(OH)D3 (r = −0.131, P < 0.001), and positively related with frailty (r = 0.131, P < 0.001). 25-(OH)D3 was negatively associated with frailty (r = −0.073, P = 0.013). And the results showed that 25-(OH)D3 was a possible mediating association between DI and frailty, which explained 10.5% of the total effect (0.0004/0.0038). Improvements in DI and increased vitamin D levels may help alleviate frailty. People should pay more attention to the diet pattern of older adults.