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

  • 2026-03-06
  • International journal for vitamin and nutrition research. Internationale Zeitschrift fur Vitamin- und Ernahrungsforschung. Journal international de vitaminologie et de nutrition 96(1)
    • Filip Max
    • Tomáš Tesař
    • Andrea Gažová
    • Juraj Smaha
    • Martin Jankovský
    • Dana Dudová
    • Peter Jackuliak
    • Martin Kužma
    • Juraj Payer
    • Ján Kyselovič

Study Design

Type
Observational
Population
30 adult patients with type 2 diabetes mellitus (T2DM) and low serum 25-hydroxyvitamin D [25(OH)D] concentrations
Methods
Prospective observational biomedical study; patients assigned to 10,000 IU/day cholecalciferol (Group A) or 960 IU/day (Group B) for 12 weeks based on recruitment order (odd/even identification numbers)
Duration
12 weeks
Funding
Unclear

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.

Research Insights

  • Vitamin D→Reduced Calcium Level

    Other metabolic markers (HbA1c, FBG, calcium, and phosphorus) remained stable over 12 weeks.

    Effect
    Neutral
    Effect size
    Small
    Dose
    10,000 IU/day (Group A) or 960 IU/day (Group B) for 12 weeks
  • Vitamin D→Reduced Fasting Blood Glucose Levels

    Other metabolic markers (HbA1c, FBG, calcium, and phosphorus) remained stable over 12 weeks.

    Effect
    Neutral
    Effect size
    Small
    Dose
    10,000 IU/day (Group A) or 960 IU/day (Group B) for 12 weeks
  • Vitamin D→Reduced Hemoglobin A1c

    Other metabolic markers (HbA1c, FBG, calcium, and phosphorus) remained stable over 12 weeks.

    Effect
    Neutral
    Effect size
    Small
    Dose
    10,000 IU/day (Group A) or 960 IU/day (Group B) for 12 weeks
  • Vitamin D→Reduced Parathyroid Hormone Levels

    PTH decreased from 3.27 to 2.76 pmol/L (median change -0.27 pmol/L)

    Effect
    Beneficial
    Effect size
    Small
    Dose
    10,000 IU/day (Group A) or 960 IU/day (Group B) for 12 weeks
  • Vitamin D→Reduced Phosphorus Level

    Other metabolic markers (HbA1c, FBG, calcium, and phosphorus) remained stable over 12 weeks.

    Effect
    Neutral
    Effect size
    Small
    Dose
    10,000 IU/day (Group A) or 960 IU/day (Group B) for 12 weeks

Adverse Events Reported

  • Vitamin D→Overall tolerability

    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

    Finding
    Reported
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