Dietary inflammatory index and mortality in middle-aged and elderly patients with metabolic syndrome.

Background: Metabolic Syndrome (MetS) significantly increases the risk of cardiovascular diseases and mortality, particularly in middle-aged and elderly populations. The Dietary Inflammation Index (DII) is a validated tool for assessing the inflammatory potential of an individual's diet, with higher scores indicating a dietary pattern that is more favorable to inflammation. The MetS population is inherently characterized by chronic low-grade inflammation, and previous studies have demonstrated an association between the DII and a wide range of chronic diseases in the general population, but little is known about the relationship between dietary inflammation and risk of death in the MetS population. This study aimed to investigate the association between DII and all-cause and cardiovascular mortality among middle-aged and elderly MetS patients.

Methods: This retrospective cohort study was based on publicly available data from the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2016. A total of 7,143 participants aged 40 years and older who were diagnosed with MetS were included. The MetS is based on the Joint Interim Statement criteria developed by the International Diabetes Federation (IDF) in 2009, which defines the MetS as the presence of any three or more of the following five items: central obesity, elevated triglycerides, lowered high-density lipoprotein (HDL) cholesterol, elevated blood pressure, and impaired glucose metabolism. Nutrient intake data were obtained from 24-hour dietary recalls. DII calculations were based on 28 food nutrient parameters, including energy, macronutrients, vitamins, minerals, and selected bioactive ingredients. Kaplan-Meier (KM) survival curves were used to analyze survival outcomes. Cox proportional hazards regression models were employed to assess the relationship between DII and mortality, with adjustments made for potential confounding factors. Restricted cubic spline (RCS) plots were used to explore the dose-response relationship.

Results: During a median follow-up period of 98 months, 1,026 participants (14.36%) died, including 284 (4.43%) from cardiovascular diseases. KM survival curves showed that higher DII quartiles were associated with lower survival rates (Log-rank P < 0.05). Cox regression results indicated that each unit increase in DII was associated with a higher risk of all-cause mortality (HR = 1.052, 95% CI: 1.006-1.100, P = 0.026) and cardiovascular mortality (HR = 1.157, 95% CI: 1.076-1.244, P < 0.001). Compared to the lowest quartile, participants in the highest DII quartile had significantly higher risks of all-cause mortality (HR = 1.289, 95% CI: 1.020-1.628, P = 0.033) and cardiovascular mortality (HR = 1.817, 95% CI: 1.194-2.764, P = 0.005). RCS analysis revealed a linear relationship between DII and both all-cause mortality (nonlinearity, P = 0.705) and cardiovascular mortality (nonlinearity, P = 0.275).

Conclusion: Higher DII scores were independently associated with increased all-cause and cardiovascular mortality among middle-aged and elderly MetS patients. Promoting an anti-inflammatory dietary pattern may be a cost-effective, non-pharmacologic approach to reducing the risk of cardiometabolic mortality in an aging population with a high cardiometabolic burden.