The discrepant effect of blood glucose on the risk of early and late lung injury: a national cohort study.

Background: The association between glycemic control and short-, and long-term lung health remains controversial. This study aimed to investigate the relationship between glucose control and overall lung health in a national cohort.

Methods: The analysis included 5610 subjects from NHANES 2007-2012. We assessed the correlation of glycemic status with respiratory symptoms (cough, sputum, wheeze, and exertional dyspnea), lung function (forced expiratory volume in 1-s (FEV1), forced vital capacity (FVC)), and obstructive or restrictive lung disease (RLD). Furthermore, we determined all-cause mortality in patients with restrictive lung disease by linking data to the National Mortality Index records up to December 31, 2019.

Results: The study involved the examination of respiratory symptoms, pulmonary function tests, and mortality analyses encompassing 3714, 3916, and 173 subjects, respectively. Multifactorial regression analyses revealed that a 1% increase in blood glucose was associated with a reduction in effect sizes (β) for FVC and FEV1 by -1.66% (-2.47%, -0.86%) and -1.94% (-2.65%, -1.23%), respectively. This increase also exhibited correlations with an elevated risk of exertional dyspnoea, restrictive ventilation dysfunction, and all-cause mortality, presenting odds ratios (ORs) of 1.19 (1.06, 1.33), 1.22 (1.10, 1.36), and 1.61 (1.29, 2.01), respectively. Regarding glycemic control, patients with improved control demonstrated stronger associations with early lung damage, significantly correlating with reduced FVC (β -10.90%, [-14.45%, -7.36%]) and FEV1 (β -9.38%, [-12.90%, -5.87%]). Moreover, they experienced a notably higher risk of exertional dyspnoea (adjusted OR 2.09, [1.35- 3.24]), while the diabetic group with poorer glycemic control showed more significant connections with advanced lung damage. This group exhibited significant associations with an increased risk of restrictive ventilatory dysfunction (adjusted OR, 2.56, [1.70-3.86]) and all-cause mortality (hazard ratios [HRs] 2.65, [1.05-6.67]), all compared to the reference group with normal glycemic metabolism.

Conclusions: Elevated blood glucose exhibited an inverse correlation with both long-term and short-term lung health. A negative L-shaped relationship was observed between glycemic control and early lung injury, along with a linearly negative association concerning late-stage lung damage. Given the cross-sectional nature of this study, a longitudinal investigation is needed to validate our findings.