What question did this study set out to answer?

This study aims to evaluate the effects of high-dose vitamin D supplementation on metabolic parameters in type 2 diabetes patients with low vitamin D levels.

March 21, 2026Open Access

Impact of High Doses of Vitamin D on Specific Metabolic Parameters in Type 2 Diabetes Patients: A Prospective Biomedical Study

FMFilip MaxComenius University Bratislava TTTomas TesarComenius University Bratislava AGAndrea GažováComenius University Bratislava

Key Points

This study aims to evaluate the effects of high-dose vitamin D supplementation on metabolic parameters in type 2 diabetes patients with low vitamin D levels.
Enrolled 30 patients with type 2 diabetes
Assigned to receive either 10,000 IU/day or 960 IU/day of cholecalciferol for 12 weeks
Measured changes in parathyroid hormone, fasting blood glucose, calcium, phosphorus, and glycated haemoglobin
High-dose vitamin D increased 25(OH)D from 17.2 to 31.8 ng/mL, while the low-dose group increased from 18.5 to 28.2 ng/mL
A significant negative correlation was found between changes in 25(OH)D and parathyroid hormone (PTH)
Other metabolic markers (HbA1c, FBG, calcium, phosphorus) remained stable over 12 weeks

Abstract

Background/Objectives: Vitamin D is a pleiotropic molecule involved in various physiological processes beyond skeletal health, including immune modulation and metabolic regulation. This prospective observational biomedical study aimed to assess the impact of short-term high-dose vitamin D supplementation on selected metabolic parameters in adult patients with type 2 diabetes mellitus (T2DM) and low serum 25-hydroxyvitamin D 25(OH)D concentrations. Methods: Thirty patients were enrolled and assigned to receive either 10,000 IU/day of cholecalciferol (Group A) or a significantly lower dose (960 IU/day, Group B) for 12 weeks based on recruitment order (odd/even identification numbers). The primary endpoints were changes in parathyroid hormone (PTH), fasting blood glucose (FBG), calcium, phosphorus, and glycated haemoglobin (HbA1c). Results: A strong, statistically significant negative correlation between changes in 25(OH)D and PTH (Spearman r = –0.69052, p = 0.0044) was also observed. In the high-dose group, 25(OH)D increased from 17.2 to 31.8 ng/mL (median change 13.3 ng/mL), while PTH decreased from 3.27 to 2.76 pmol/L (median change –0.27 pmol/L). In the lower-dose group, 25(OH)D increased from 18.5 to 28.2 ng/mL (median change +8.1 ng/mL). The increase in 25(OH)D was significantly greater in the high-dose group than in the lower-dose group (median change +13.3 vs +8.1 ng/mL, p = 0.015). Within the observed range, patients with larger increases in 25(OH)D tended to show greater reductions in PTH. Other metabolic markers (HbA1c, FBG, calcium, and phosphorus) remained stable over 12 weeks. Conclusions: These findings support the effectiveness and safety of high-dose vitamin D supplementation in correcting vitamin D deficiency and reducing PTH levels in patients with T2DM while highlighting the need for longer-term studies to evaluate its broader metabolic effects.

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