Insulin resistance as a mediator of the associations between visceral adiposity and preserved ratio impaired spirometry

Preserved ratio impaired spirometry (PRISm) is a prevalent but under-recognized spirometric phenotype associated with increased morbidity and mortality. Metabolic obesity and insulin resistance have been associated with lung function impairment; however, their interrelationships with PRISm remain insufficiently characterized. We hypothesized that obesity-related indices reflecting visceral and central adiposity are associated with PRISm and that insulin resistance may statistically account for part of these associations. Using the data from 4979 adults in the National Health and Nutrition Examination Survey (NHANES), visceral adiposity index (VAI), lipid accumulation product (LAP), waist-to-height ratio (WHtR), and insulin resistance (HOMA-IR) were analyzed in relation to PRISm. Multivariable logistic regression, restricted cubic spline (RCS) models, and counterfactual-based mediation analyses were applied. Higher VAI, LAP, and WHtR were independently associated with a higher likelihood of PRISm, with significant dose–response and nonlinear relationships (all p < 0.01). Elevated HOMA-IR was also associated with PRISm (Q4 vs Q1: OR = 2.27, 95% CI 1.46–3.52). Mediation analyses indicated that insulin resistance was statistically compatible with partial mediation in the associations between adiposity indices and PRISm, explaining 9.2–32.8% of the observed associations. These cross-sectional findings are consistent with a model in which insulin resistance statistically mediates part of the association between central adiposity and PRISm, under the assumptions of the mediation analysis. These findings highlight potentially relevant metabolic correlates of PRISm; however, implications for prevention or intervention require confirmation in longitudinal and mechanistic studies.