The Association Between Vitamin D Deficiency and the Level of Fasting C Peptide Among Patients With Uncontrolled Type 2 Diabetes Mellitus: A Retrospective Cohort Study

This study investigates the relationship between vitamin D deficiency and uncontrolled type 2 diabetes mellitus (T2DM) indicated by elevated glycosylated hemoglobin (HbA1c) levels, and assesses the association between fasting C peptide levels and uncontrolled T2DM, given their roles in β-cell function and insulin secretion. A retrospective cohort design was used, enrolling adults with T2DM with baseline vitamin D, fasting C peptide, and HbA1c data. Data were collected from electronic medical records with follow-up after three months. Binary logistic regression analyses explored associations between vitamin D and C peptide levels and uncontrolled T2DM (HbA1c > 7%). Point estimates suggested that higher vitamin D (B = -0.097) and C peptide (B = -0.222) levels were associated with lower odds of uncontrolled diabetes, though these associations were not statistically significant. Overall, higher vitamin D and C peptide levels appeared to correlate with decreased likelihood of uncontrolled diabetes, warranting further investigation.