Impact of Diabetes on the Lungs

New research suggests that A1c may play a more prominent role than the duration of diabetes when it comes to the lungs and respiratory function.

When thinking about the risks associated with diabetes mellitus, it becomes apparent that diabetes can affect the whole body due to vascular damage and complications. While organs such as the kidneys, eyes, and heart are commonly brought up regarding organ dysfunction secondary to diabetes, other organs like the lungs are left out. Damage to the microvascular can cause reduced lung elasticity, which can then lead to lung function impairment. Klein et al. saw a reduction in forced vital capacity (FVC), forced expiratory volume (FEV1), and carbon monoxide diffusing capacity when comparing pulmonary function between patients with and without diabetes. However, it is still unclear whether the duration of diabetes or A1c level has a more significant impact on lung function.

A recent case-controlled cross-sectional study conducted at a university hospital in Saudi Arabia looked to see which of the two factors had a more significant correlation with lung function. For inclusion criteria, subjects must have a history of type 2 diabetes (T2DM), be aged 30-65 years old, have a BMI < 30 kg/m2, and have a fasting blood glucose ≥ 126 mg/dL or an A1c > 6.5%. The investigators picked healthy subjects from the university staff that did not have any chronic conditions like diabetes and hypertension to be a part of the control group. Subjects were not eligible if they had obesity, smoked tobacco products, had a history of type 1 diabetes or diabetic micro-/macrovascular complications, abnormality in vertebral column or thoracic cage that would affect respiratory function, cancer, or had thoracoabdominal surgery. To quantify lung function, participants underwent spirometry to measure their vital capacity (VC), FVC, FEV1, FEV1/FVC, forced expiratory flow at 25%, 50%, and 75% (FEF-25%/50%/75%), FEF-25-75%, and peak expiratory flow (PEF). A two-independent sample t-test compared the lung function between the two groups overall and when stratified by duration of diabetes (≤5 years, between 5 to 10 years, and >10 years) and A1c (≤8% or >8%). Pearson correlation determined the relationship between duration of diabetes and A1c with respiratory function. Finally, the investigators used binary logistic regression analysis to compare the log-odds in lung function parameters. 

A total of 202 patients (n=101 in each arm) participated in the study (mean age 55 years, 70% female, mean duration of diabetes 17 years). Differences in lung function varied when stratified based on the duration of diabetes. There was no significant difference in lung function parameters for patients diagnosed ≤5 years ago between the two groups (p>0.05). However, unlike patients with a shorter duration of diabetes, patients with a diagnosis between 5-10 years ago had significantly lower FEV1/FVC ratio (86.39±6.79% vs. 91.47±5.97%, respectively), FEF-50%, and FEF-75% when compared to the control group (p<0.05 for all). Finally, investigators only saw a significant reduction in FEV1 (2.64±0.61 L/sec vs. 2.90±0.68 L/sec, respectively) for patients with a duration >10 years. When stratifying the data by A1c, patients with an A1c <8% had significantly lower FEV1/FVC (p<0.006) and FEF-50% (p<0.034), while patients with an A1c >8% had substantially lower VC, FVC, FEV1, PEFR, and FEF-25-75% (p<0.05 for all) but not FEV1/FVC when compared to the control group. Using these results, the investigators identified a significant inverse correlation between A1c and VC, FVC, FEV1, and FEF-25%/50%/75% (p<0.05). Surprisingly, they saw no significant correlation between the duration of diabetes and lung function parameters, and regression analysis did not show significant reductions in VC, FVC, FEV1, PEF, and FEF25-75%.

Based on the present study, it appears that having elevated A1c levels is more likely to affect lung function than the duration of diabetes. Studies like one performed by Tai et al. have shown negative relationships between A1c/duration of diabetes and lung function. By stratifying both, the authors determined which factor has a more significant effect. For future studies, it would be interesting to see how improvements in A1c affect these parameters. With increasing evidence that diabetes may affect lung function, it may become more important to counsel patients about it along with other complications associated with diabetes.  

Practice Pearls

• High A1c levels are inversely related to pulmonary function parameters like VC, FVC, FEV1, and FEF. 
• Elevated A1c causes more damage to the lungs than having a long duration of therapy.
• Glycemic control may be crucial to prevent respiratory complications in patients with T2DM, especially if they have other risk factors. 

References for “Impact of Diabetes on the Lungs””
Maan, Hawra Bin et al. “Effect of Glycated Hemoglobin (HbA1c) and Duration of Disease on Lung Functions in Type 2 Diabetic Patients.” International journal of environmental research and public health vol. 18,13 6970. 29 Jun. 2021, doi:10.3390/ijerph18136970

Klein, O L et al. “Lung spirometry parameters and diffusion capacity are decreased in patients with Type 2 diabetes.” Diabetic medicine: a journal of the British Diabetic Association vol. 29,2 (2012): 212-9. doi:10.1111/j.1464-5491.2011.03394.x

Tai, He et al. “Vascular Endothelial Function as a Valid Predictor of Variations in Pulmonary Function in T2DM Patients Without Related Complications.” Frontiers in endocrinology vol. 12 622768. 11 Mar. 2021, doi:10.3389/fendo.2021.622768

Andy Dao, PharmD Candidate, University of South Florida Taneja College of Pharmacy