Association between the dietary index for gut microbiota (DI-GM) and all-cause mortality in older adults with COPD: Evidence from the NHANES

Chronic obstructive pulmonary disease (COPD) is a major cause of death, especially among older adults. Dietary patterns may affect COPD prognosis through the gut-lung axis by modulating inflammation and immune balance. This study investigated the association between the dietary index for gut microbiota (DI-GM) and all-cause mortality in older COPD patients. Data were derived from the National Health and Nutrition Examination Survey 2007 to 2018. A total of 946 participants aged ≥65 years with COPD were included. DI-GM scores were calculated using 24-hour dietary recalls based on 14 food and nutrient components reflecting favorable or unfavorable effects on gut microbiota. Participants were categorized into quartiles (Q1–Q4), with Q1 as the reference group. The primary outcome was all-cause mortality. Kaplan–Meier survival curves, Cox proportional hazards models, and restricted cubic spline analyses were used to evaluate the relationship between DI-GM and mortality risk. Subgroup analyses were performed to test the robustness of the associations. During a median follow-up of 92 months, 304 deaths (32.1%) were recorded. Higher DI-GM scores were significantly associated with a lower risk of all-cause mortality. Compared with Q1, individuals in Q4 had a 35% lower mortality risk after full adjustment (hazard ratio = 0.51, 95% confidence interval: 0.37–0.70, P < .001). Restricted cubic spline analysis revealed a linear inverse association between DI-GM and mortality risk ( P -overall = .001; P -nonlinear > .05). Subgroup analyses showed consistent associations across most strata, with stronger protective effects observed among participants with higher poverty-income ratios ( P for interaction = .021). Higher DI-GM scores were independently associated with lower all-cause mortality among older adults with COPD. These findings support a potential link between diet quality related to gut microbiota and long-term outcomes, although causality cannot be inferred.