Diabetes mellitus is a rapidly increasing metabolic disorder associated with significant microvascular and macrovascular complications, leading to substantial morbidity and mortality. While the classical target organs include the kidneys, eyes, and cardiovascular system, emerging evidence indicates that the lung is also affected by chronic hyperglycemia. According to the International Diabetes Federation, approximately 537 million adults were living with diabetes worldwide in 2021, including nearly 77 million in India, with projections rising to 134 million by 2045 [1]. Chronic hyperglycemia results in microangiopathic changes such as basement membrane thickening in pulmonary capillaries, similar to those seen in diabetic nephropathy and retinopathy, leading to impaired alveolar–capillary gas exchange and reduced diffusion capacity [2]. In addition, non-enzymatic glycation of collagen and elastin alters lung elasticity, contributing to restrictive ventilatory defects [3]. T2DM is also associated with low-grade systemic inflammation, which may promote airway remodelling and small airway dysfunction, even in asymptomatic individuals [4]. Pulmonary function tests (PFTs), particularly spirometry, provide a simple and effective method for detecting early and subclinical pulmonary involvement. some studies have reported significant reductions in forced vital capacity (FVC) and forced expiratory volume in one second (FEV₁) among patients with T2DM, with relative preservation of the FEV₁/FVC ratio, suggesting a predominantly restrictive pattern [3,5]. Recent studies have further demonstrated that impaired pulmonary function in T2DM is associated with microvascular complications, poor glycemic control, and increased risk of cardiovascular morbidity and mortality [6-8]. Despite growing evidence, pulmonary involvement in T2DM remains under-recognized in routine clinical practice, particularly in India, where limited data are available. This study was therefore undertaken to assess pulmonary function in patients with Type 2 Diabetes Mellitus at a tertiary care center and to compare the findings with healthy controls, with the aim of facilitating early detection and improving clinical monitoring.

This cross-sectional study was conducted in the Outpatient and Inpatient Departments of General Medicine at F.H. Medical College and Hospital, Agra, over a period of 18 months. The study included patients diagnosed with T2DM attending the Department of Medicine, along with age-matched healthy individuals who served as controls. A total of 122 participants were enrolled in the study. Patients aged 25–65 years with a confirmed diagnosis of T2DM and a minimum disease duration of three years were included after obtaining written informed consent. Healthy individuals within the same age group were included as controls. Patients with a history of smoking, acute or chronic respiratory diseases, cardiovascular diseases, chronic kidney disease, neuromuscular disorders, occupational exposure to respiratory irritants, musculoskeletal deformities affecting lung function (such as kyphoscoliosis), or inability to perform pulmonary function tests were excluded from the study. After explaining the study objectives and procedures, all participants completed a pre-structured questionnaire capturing relevant demographic and clinical details. A detailed medical history and thorough physical examination were performed at the time of enrolment. Information regarding current medications and relevant clinical parameters was recorded. Anthropometric measurements were obtained, and body mass index (BMI) was calculated using the standard formula. Pulmonary function tests were performed in both the diabetic and control groups using a computerized spirometer (RMS Helios 401, Recorders & Medicare Systems Pvt. Ltd., India), in accordance with the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines. Each participant performed three acceptable spirometry maneuvers at 15-minute intervals, and the best of the three readings was considered for analysis. The parameters assessed included forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), FEV₁/FVC ratio, forced expiratory flow between 25% and 75% of FVC (FEF₂₅–₇₅%), slow vital capacity (SVC), and maximum voluntary ventilation (MVV). Predicted values were calculated based on age, height, and weight, and results were expressed as percentages of predicted values. The study was conducted after obtaining informed consent from all participants, and confidentiality and anonymity were maintained throughout the study. No additional investigations were performed exclusively for research purposes, and all patients continued to receive standard treatment as per existing clinical guidelines. Data were entered into Microsoft Excel and analyzed using SPSS software. Categorical variables were expressed as frequencies and percentages, while continuous variables were presented as mean ± standard deviation. Appropriate statistical tests were applied, and a p-value of <0.05 was considered statistically significant.

This study was conducted on 244 patients out of which 122 were patients of diabetes mellitus and 122 were control with same age sex and mortality. The demographic distribution of cases showed that the majority of patients belonged to the 30–50 years age group, accounting for 69 cases (56.6%). Patients aged more than 50 years constituted 47 cases (38.5%), while only 6 cases (4.9%) were below 30 years of age. These findings indicate that the condition was most commonly observed in the middle-aged population. Table 1. Age, Sex Distribution and Duration of Diabetic Patients (n = 122). Variable Category Cases (n) Percentage (%) Age group <30 years 6 4.9 30–50 years 69 56.6 >50 years 47 38.5 Gender Male 71 58.2 Female 51 41.8 Graph 1 A. Age, Distribution and Duration of Diabetic Patients (n = 122). Graph 1 B: Sex Distribution and Duration of Diabetic Patients (n = 122). Gender-wise distribution revealed a male predominance, with 71 cases (58.2%) compared to 51 female cases (41.8%). This suggests that males were more frequently affected than females in the present study population. Table 2. Cases According to HbA1c, BMI and Treatment Modality (n = 122). Variable Category Cases (n) Percentage (%) Duration of DM <5 years 75 61.5 5–10 years 34 27.9 ≥10 years 13 10.7 HbA1c <8 % 43 35.2 ≥8 % 79 64.8 BMI <25 kg/m² 69 56.6 25–30 kg/m² 53 43.4 Treatment Oral Hypoglycemic Agents (OHA) 101 82.8 Insulin 21 17.2 Graph 2 A. Cases According to Duration of DM. Graph 2 B. Cases According to HbA1c Graph 2 C. Cases According to BMI. Graph 2 D. Cases According to Treatment. The distribution of cases based on the duration of diabetes mellitus revealed that the majority of patients had diabetes for less than 5 years, accounting for 75 cases (61.5%). Patients with a disease duration of 5–10 years constituted 34 cases (27.9%), while those with diabetes for 10 years or more comprised 13 cases (10.7%). Assessment of glycemic control using HbA1c levels showed that 79 patients (64.8%) had HbA1c values ≥8%, indicating poor glycemic control, whereas 43 patients (35.2%) had HbA1c levels below 8%. Regarding body mass index, most patients had BMI less than 25 kg/m² (56.6%), while 43.4% of patients had BMI between 25 and 30 kg/m². In terms of treatment modality, the majority of patients (82.8%) were managed with oral hypoglycemic agents, whereas 17.2% of patients were receiving insulin therapy. These findings suggest that a significant proportion of patients had relatively shorter disease duration but demonstrated suboptimal glycemic control, with most being managed on oral medications. Table 3. Comparison of Pulmonary Function Test (PFT) Patterns Between Case and Control Groups (n = 244). Group Normal n (%) Restrictive n (%) Obstructive n (%) Total n (%) P value Control (n = 122) 122 (91.8%) 0 0 122 (50.0%) < 0.001* Case (n = 122) 71 (58.2%) 34 (27.9%) 17 (13.9%) 122 (50.0%) Total (n = 244) 183 (75.0%) 41 (16.8%) 20 (8.2%) 244 (100%) Graph 3. Comparison of Pulmonary Function Test (PFT) Patterns Between Case and Control Groups (n = 244). Pulmonary function patterns differed significantly between cases and controls. Most controls had normal spirometry (91.8%), whereas only 58.2% of cases showed normal pulmonary function. Among cases, restrictive and obstructive patterns were observed in 27.9% and 13.9%, respectively. Overall, abnormal pulmonary function was significantly more common in cases than controls (p < 0.001), indicating a strong association between disease status and impaired lung function. Table 4: Correlation of duration of diabetes with different PFT parameters (n = 122). Parameter <5 years (n=75) 5–10 years (n=34) ≥10 years (n=13) FVC (%Pred.) 0.777 ± 0.181 0.729 ± 0.244 0.70 ± 0.172 FEV1 (%Pred.) 0.733 ± 0.208 0.614 ± 0.260 0.60 ± 0.149 FEV1/FVC (%Pred.) 0.929 ± 0.160 0.887 ± 0.132 0.82 ± 0.113 PEFR (%Pred.) 0.513 ± 0.196 0.444 ± 0.146 0.41 ± 0.213 FEF25–75% (%Pred.) 0.559 ± 0.202 0.397 ± 0.185 0.37 ± 0.208 P value table: Parameter <5 vs 5–10 yrs <5 vs ≥10 yrs 5–10 vs ≥10 yrs FVC (%Pred.) p ≈ 0.31 (NS) p = 0.95(NS) p ≈ 0.54 (NS) FEV1 (%Pred.) p ≈ 0.03 (Significant) p ≈ 0.35 (NS) p ≈ 0.15 (NS) FEV1/FVC (%Pred.) p ≈ 0.25 (NS) p ≈ 0.25 (NS) p ≈ 0.29 (NS) PEFR (%Pred.) p ≈ 0.23 (NS) p ≈ 0.48 (NS) p ≈ 0.35 (NS) FEF25–75% (%Pred.) p < 0.001 (Highly Significant) p ≈ 0.39 (NS) p ≈ 0.22 (NS) Graph 4: Correlation of duration of diabetes with different PFT parameters (n = 122). Table 4 demonstrates the relationship between duration of diabetes and various pulmonary function test (PFT) parameters among 122 patients. A progressive decline in mean values of FVC, FEV₁, FEV₁/FVC ratio, PEFR, and FEF25-75 % is observed with increasing duration of diabetes, suggesting worsening pulmonary function as disease duration increases. Patients with diabetes duration of less than 5 years showed comparatively better pulmonary function across all parameters, while those with a duration of 10 years or more had the lowest mean values. On statistical comparison, the reduction in FEV₁ between patients with diabetes duration of less than 5 years and those with 5–10 years was found to be statistically significant (p ≈ 0.03). Additionally, FEF₂₅–₇₅% showed a highly significant decline between these two groups (p < 0.001), indicating early involvement of small airways with increasing disease duration. However, differences in FVC, FEV₁/FVC ratio, and PEFR across the groups were not statistically significant. but there is linear decline in all parameters in relation to duration of diabetes. Overall, the findings suggest that longer duration of diabetes is associated with a decline in pulmonary function, particularly affecting expiratory flow rates and small airway function. Table 5: Comparison of PFT Parameters Between Case and Control Groups (n = 244). Parameter Case Group (n = 122) Control Group (n = 122) Welch t-test p-value FVC (%Pred.) 0.752 ± 0.178 0.911 ± 0.082 < 0.001* FEV₁ (%Pred.) 0.798 ± 0.186 0.935 ± 0.098 < 0.001* FEV₁/FVC (%Pred.) 0.956 ± 0.128 0.972 ± 0.094 0.318 PEFR (%Pred.) 0.542 ± 0.178 0.692 ± 0.121 0.002* FEF₂₅–₇₅% (%Pred.) 0.581 ± 0.205 0.728 ± 0.162 0.001* Graph 5: Comparison of PFT Parameters Between Case and Control Groups (n = 244). Table 5 compares the Pulmonary Function Test (PFT) parameters between the case group and control group comprising 122 subjects each. It was observed that the mean values of FVC (% predicted), FEV₁ (% predicted), PEFR (% predicted), and FEF₂₅–₇₅% (% predicted) were significantly lower among cases as compared to controls (p < 0.05). This indicates a notable reduction in pulmonary function among cases, suggesting impaired ventilatory capacity. However, the FEV₁/FVC ratio was also declined as compared to control but did not show a statistically significant difference (p = 0.318), implying that the predominant pattern of abnormality in the case group is restrictive rather than obstructive in nature. Overall, these results highlight that the case group exhibits a significant decline in lung function parameters compared to healthy controls.

The present study evaluated pulmonary function in patients with type 2 diabetes mellitus and demonstrated a significantly higher prevalence of spirometric abnormalities compared to healthy controls. Pulmonary dysfunction was observed in a substantial proportion of diabetic patients, while almost all controls had normal lung function, indicating a clear association between diabetes and impaired respiratory mechanics. These findings support the concept that the lung may be affected as a target organ in diabetes, even in the absence of overt respiratory symptoms. Most patients in the present study belonged to the middle-aged group, with a mild male predominance, a demographic pattern similar to that reported in previous Indian studies by Patel et al. [9] and Barik et al. [10] Earlier studies have also shown that pulmonary impairment in diabetes is commonly detected in the productive age group, suggesting that long-term metabolic exposure rather than aging alone contributes to lung involvement. The majority of patients had a diabetes duration of less than five years, yet poor glycemic control was common, a finding consistent with earlier reports that emphasize the role of sustained hyperglycemia in the development of microvascular complications, including those affecting the lung. Restrictive ventilatory defects were the most frequent abnormality observed in the present study, followed by obstructive changes. Similar patterns have been reported by Patel et al. [9], and Kumar et al. [11], who also documented a predominance of restrictive lung involvement among diabetic patients. The preservation of the FEV₁/FVC ratio with significant reductions in FVC and FEV₁ observed in this study further supports a restrictive pattern, suggesting reduced lung compliance rather than primary airway obstruction. Reduced PEFR and FEF₂₅–₇₅% values indicate early small airway involvement, a finding that aligns with observations made by Thakorbhai et al. [12]. A progressive decline in pulmonary function parameters with increasing duration of diabetes was noted, particularly affecting FEV₁ and mid-expiratory flow rates. Comparable trends have been described in earlier studies, where longer disease duration was associated with greater impairment of lung function. However, the lack of significant change in the FEV₁/FVC ratio across duration groups in the present study, as also reported by Patel et al.[9], suggests that airway obstruction is not the dominant mechanism of pulmonary involvement in diabetes. Body mass index did not show a significant association with pulmonary function parameters, a finding consistent with several previous studies that reported pulmonary impairment independent of obesity. This further strengthens the hypothesis that metabolic and microvascular alterations related to chronic hyperglycemia, such as non-enzymatic glycosylation of lung connective tissue, thickening of the alveolar–capillary membrane, low-grade inflammation, and detailed pathological changes, play a central role in the pathogenesis of diabetic lung involvement. Overall, the findings of the present study suggest that pulmonary function declines with increasing duration of diabetes and are in agreement with existing literature, confirming that pulmonary dysfunction is a common but under-recognized complication of type 2 diabetes mellitus. Hence, it is essential to increase awareness and incorporate routine pulmonary function assessment as part of comprehensive diabetes management. Overall, the findings of the present study are in agreement with existing literature and confirm that pulmonary dysfunction is a common but under-recognized complication of type 2 diabetes mellitus. The similarity of results with previous studies highlights the need for increased clinical awareness and consideration of routine pulmonary function assessment as part of comprehensive diabetes management.

This study demonstrates that diabetes mellitus is significantly associated with impaired pulmonary function. Diabetic patients showed reduced FVC, FEV₁, PEFR, and FEF₂₅–₇₅% compared to controls, with a predominantly restrictive pattern of abnormality. A linear decline in lung function parameters was observed with increasing duration of diabetes, particularly affecting expiratory flow rates and small airway function. These findings suggest that pulmonary dysfunction is a progressive and under-recognized complication of diabetes, highlighting the importance of routine pulmonary function assessment in diabetic patients.

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