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.