High Doses of Vitamin D and Specific Metabolic Parameters in Type 2 Diabetes Patients: Systematic Review

Background/Objectives: Type II diabetes mellitus (T2DM) is recognized as a condition of mild chronic inflammation, marked by increased levels of acute-phase proteins and various inflammatory indicators. These inflammatory substances, along with inflammation of adipose tissue and the secretion of adipocytokines, can contribute to insulin resistance and β cell dysfunction. By influencing both innate and adaptive immunity, vitamin D can inhibit the production of inflammatory cytokines and help mitigate the low-grade chronic inflammation associated with T2DM. Several strategies have been proposed to increase vitamin D levels effectively and safely, but the recent and strong ones have common tactics. Short-term high doses increase the level acutely, and long-term lower doses maintain sufficient levels. Methods: The aim of our work was to determine and verify the effectiveness of high doses of vitamin D to safely increase its level in patients with type 2 diabetes mellitus, as well as the effect of these doses on selected metabolic parameters. Data from 20 studies (vitamin D group n = 612, and control group n = 592) regarding the influence of vitamin D supplementation with doses above 4000 IU on serum 25(OH)D, fasting blood glucose (FBG), hemoglobin A1c (HbA1c), blood pressure, serum calcium, and parathormone were pooled. Results: Vitamin D supplementation significantly improved serum 25(OH)D levels, with an average increase after intervention versus baseline at 177.09%. Our studies suggest that vitamin D supplementation may benefit various parameters in T2DM patients, including glycemic control, blood pressure, and PTH levels. Conclusions: Vitamin D supplementation may have beneficial effects on various parameters in type 2 diabetes patients, including glycemic control, blood pressure, and parathormone levels. However, the results are only sometimes consistent across all studies. Further examination is needed.