The goal of this clinical study is to learn whether vitamin D supplementation improves metabolic control in adults with type 2 diabetes mellitus who have vitamin D deficiency.

The main questions it aims to answer are:

Does vitamin D supplementation improve fasting glucose and glycated hemoglobin (HbA1c) levels in patients with type 2 diabetes and vitamin D deficiency? Does vitamin D supplementation increase serum vitamin D concentrations in these patients?

Researchers will evaluate metabolic parameters before and after vitamin D supplementation to assess changes associated with correction of vitamin D deficiency.

Participants will:

Receive oral vitamin D supplementation (100,000 IU once monthly) for three months Have fasting glucose, HbA1c, body mass index (BMI), and serum vitamin D levels measured at baseline and after three months of supplementation.

Vitamin D deficiency is highly prevalent among individuals with type 2 diabetes mellitus and has been associated with alterations in glucose metabolism, insulin resistance, and systemic inflammation. Several studies suggest that vitamin D may play a role in pancreatic beta-cell function and insulin sensitivity; however, evidence regarding the metabolic effects of vitamin D supplementation in patients with diabetes remains inconsistent.

The aim of this study was to evaluate changes in metabolic parameters after correction of vitamin D deficiency in adults with type 2 diabetes mellitus.

This longitudinal single-arm interventional study included 119 consecutive adult patients with type 2 diabetes mellitus and confirmed vitamin D deficiency. Patients with conditions that could interfere with vitamin D metabolism or absorption, including chronic kidney disease, intestinal malabsorption syndromes, and pregnancy, were excluded.

Participants received oral cholecalciferol supplementation at a dose of 100,000 IU once monthly for three months. Clinical and biochemical parameters were evaluated at baseline and after the intervention period. Measurements included fasting glucose, glycated hemoglobin (HbA1c), body mass index (BMI), and serum vitamin D concentrations.

The study aimed to assess changes in metabolic control following vitamin D supplementation and to explore the potential role of correcting vitamin D deficiency in patients with type 2 diabetes mellitus.

Inclusion Criteria:

• Adults (≥18 years) of both sexes.
• Diagnosis of type 2 diabetes mellitus (T2DM).
• Patients treated at the Endocrinology Service of the Hospital de Clínicas, Facultad de Ciencias Médicas, Universidad Nacional de Asunción (FCM-UNA), or in private clinical practice between May and September 2024.
• Serum 25-hydroxyvitamin D [25(OH)D] deficiency < 30 ng/mL.
• Participants who adhered to the prescribed vitamin D supplementation for a period of three months.

Exclusion Criteria:

• Patients with intestinal malabsorption disorders (e.g., celiac disease, Crohn's disease, or other disorders affecting calcium absorption).
• Pregnant women.
• Patients already taking vitamin D supplementation at the time of study initiation.
• Patients with chronic kidney disease.
• Patients with a history of bariatric surgery

Individual participant data will not be publicly available. Data may be available from the investigators upon reasonable request and subject to institutional and ethical approval.