Associations of metabolic syndrome with lung function decline and clinical respiratory outcomes: the NHLBI Pooled Cohort Study

Background Whether metabolic syndrome (MetS) increases the risk of chronic lung diseases remains uncertain. We aimed to test whether MetS was associated with lung function and clinical respiratory outcomes. Methods Data were harmonised from six US general population-based prospective cohorts. Participants with baseline airflow limitation (forced expiratory volume in 1 s (FEV₁):forced vital capacity (FVC) <0.70), restriction (FEV₁:FVC ⩾0.7, FVC <80%), clinical chronic lower respiratory disease (CLRD) or cardiovascular disease were excluded. MetS was defined at baseline as the presence of at least three of the following: central obesity, high triglycerides, low high-density lipoprotein cholesterol, high blood pressure (BP) and high fasting glucose. Associations with lung function decline and incident clinical respiratory events were tested in linear mixed models and Cox models, respectively, adjusted for sociodemographic, anthropometric, smoking and clinical factors. The five subcomponents of MetS were evaluated separately in secondary analyses. Results Of 15 728 participants (mean age 49.6 years, 57.6% female, 68.6% White, 27.0% Black), 4422 (28.1%) had MetS. In fully adjusted models that included body weight, MetS was associated with greater rate of FVC decline (−0.89 mL·year⁻¹, 95% CI −1.73– −0.05) and incident restriction (1085 cases, hazard ratio 1.52, 95% CI 1.30–1.77), but not FEV₁ decline, incident airflow limitation or clinical respiratory outcomes. Among the subcomponents of MetS, central obesity, high BP and high fasting glucose were associated with incident restriction, while high BP alone was associated with incident airflow limitation, CLRD-related events and respiratory-related mortality. Conclusions MetS was associated with accelerated FVC decline and incident restriction, but not incident obstruction, in healthy adults.