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The underlying mechanism in both cognitive impairment and depression was chronic inflammation, which could be reflected by the dietary inflammatory index (DII). However, the effect of cognitive impairment on the association between DII and depression was not clear. Therefore, in this study, we hypothesized that cognitive impairment could mediate the association between dietary inflammation and depressive symptoms. A total of 2550 participants aged ≥60 from the National Health and Nutrition Examination Survey (NHANES) in 2011-2014 were involved in the serial, cross-sectional study. Proinflammatory and anti-inflammatory diets were measured by DII. Cognitive impairment was measured by four dimensions, CERAD-immediate, CERAN-delayed, animal fluency test, and DSST. Depressive symptoms were measured by PHQ-9 scores. We found that a proinflammatory diet and cognitive impairment were both risk factors for depressive symptoms. An interaction between an inflammatory diet and cognitive impairment was detected ( P -interaction = 0.060). In addition, all four dimensions of cognition mediated the association between DII and depressive symptom scores. Part of the association between DII and depressive symptoms scores could be explained by different dimensions of cognitive function, and the proportion of mediation ranged from 10.0% to 36.7%. In conclusion, cognitive impairment levels partly mediated the association between DII and depressive symptoms.

Background: Dietary inflammatory index (DII) was associated with Type 2 diabetes mellitus and cognitive function impairment (CFI).Objective: The aim of this study was to explore whether the associations among DII, glycohemoglobin (HbA1c), and CFI were similar in the participants with or without diabetes.Methods: A total of 1,198 participants aged 60 and over from the National Health and Nutrition Examination Survey (NHANES) in 2011-2014 were involved in this study, dividing into subgroups as diabetes and non-diabetes for further analysis.Results: We found that participants with pro-inflammatory diet had higher proportion of CFI patients (p < 0.05). Pro-inflammatory diet and HbA1c were positively associated with the risk of CFI; participants with pro-inflammatory diet was 1.479 times on occurrence of CFI compared with anti-inflammatory diet group. The interaction between inflammatory diet and HbA1c was positive on the risk of CFI and was negative on the CERAD-immediate and CERAD-delayed, respectively. Among the participants without diabetes, the associations of Energy-adjusted DII (E-DII) with Animal Fluency test and Digit Symbol Substitution Test (DSST) were partially mediated by HbA1c, and the mediated proportion was 5.8% and 6.6%, respectively. However, there was no such mediation effect in the diabetes patients.Conclusion: In elderly participants without diabetes, there was an interaction between inflammatory diet and HbA1c on the association with CFI, especially for the dimension of CERAD-immediate and CERAD-delayed. Besides, the associations of E-DII with Animal Fluency test and DSST were partially mediated by HbA1c. For diabetic patients, HbA1c, rather than the inflammatory diet has a positive effect on the CFI risk. [ABSTRACT FROM AUTHOR]