Relationship between serum 25-hydroxyvitamin D and indicators of glucose metabolism in inpatients with type 2 diabetes mellitus

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Objective To investigate the correlation between 25-hydroxyvitamin D [25(OH)D] and indicators of glucose metabolism in inpatients with type 2 diabetes mellitus. Method We retrospectively analyzed the clinical records of 214 inpatients with type 2 diabetes mellitus, including age, body mass index (BMI), systolic blood pressure, diastolic blood pressure, and laboratory test results such as serum parathyroid hormone (PTH), 25(OH)D, creatinine, calcium, phosphorus, glycosylated hemoglobin A1c (HbA1c), fasting blood glucose, and fasting insulin. Results The prevalence of vitamin D deficiency was high in these patients, with 47.2% of them having a serum 25(OH)D concentration lower than 10 ng/ml. Using 25(OH)D level less than 10 ng/ml as the cut-off point, the patients were divided into vitamin D severe deficiency (Vit-SD) group and vitamin D non-severe deficiency (Vit-NSD) group. Compared with the Vit-NSD group, the Vit-SD group had younger age [(55.27±13.71) years vs. (60.76±12.32) years, P=0.001] and higher HbA1c level [(9.00±2.01)% vs. (8.45±1.86)%, P=0.025]. BMI [ (25.09±4.01)kg/m2vs. (25.39±3.53)kg/m2,P=0.523], fasting blood glucose [(8.91±3.31)mmol/L vs. (8.16±3.02)mmol/L, P=0.063], fasting serum insulin [(21.32±32.50)mIU/L vs. (21.92±26.95)mIU/L, P=0.873] and homeostasis model assessment of insulin resistance index (97.60±8.92 vs. 7.53±9.39, P=0.954) in these two groups were with no statistically significant difference. The association analyses showed that HbA1c was significantly negatively correlated with 25(OH)D (r=-0.190, P=0.003) and not correlated with serum PTH, calcium, or phosphorus, after adjusting for age and creatinine. Multiple linear regression revealed that HbA1c had a significantly negative correlation with age (β=-0.220, P=0.000) and 25(OH)D (β=-0.184, P=0.000). Conclusions There is high prevalence of vitamin D deficiency in inpatients with type 2 diabetes mellitus, which is even higher in relatively young patients. Serum 25 (OH) D may be negatively correlated with HbA1c in these patients independently from age, BMI, fasting serum insulin, and homeostasis model assessment of insulin resistance index. Key words: Diabetes mellitus; 25-hydroxyvitamin D; Parathyroid hormone; Glycosylated hemoglobin; Glucose metabolism