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.

It is unclear how ongoing inflammation in Coronavirus Disease 2019 (COVID-19) affects 25-hydroxyvitamin D (25[OH]D) concentration. The objective of our study was to examine serum 25(OH)D levels during COVID-19 pneumonia. Patients were admitted between 1 November and 31 December 2021. Blood samples were taken on admission (day 0) and every 24 h for the subsequent four days (day 1–4). On admission, 59% of patients were 25(OH)D sufficient (>30 ng/mL), and 41% had 25(OH)D inadequacy (<30 ng/mL). A significant fall in mean 25(OH)D concentration from admission to day 2 (first 48 h) was observed (30.7 ng/mL vs. 26.4 ng/mL; p < 0.0001). No subsequent significant change in 25(OH)D concentration was observed between day 2 and 3 (26.4 ng/mL vs. 25.9 ng/mL; p = 0.230) and day 3 and day 4 (25.8 ng/mL vs. 25.9 ng/mL; p = 0.703). The absolute 25(OH)D change between hospital admission and day 4 was 16% (4.8 ng/mL; p < 0.0001). On day 4, the number of patients with 25(OH)D inadequacy increased by 18% (p = 0.018). Therefore, serum 25(OH)D concentration after hospital admission in acutely ill COVID-19 patients should be interpreted with caution. Whether low 25(OH)D in COVID-19 reflects tissue level vitamin D deficiency or represents only a laboratory phenomenon remains to be elucidated in further prospective trials of vitamin D supplementation.

The coronavirus disease 2019 (COVID-19) pandemic has led to changes in lifestyle, which could influence vitamin D status on a population level. The purpose of our study was to compare 25-hydroxyvitamin D (25[OH]D) levels in patients hospitalized because of severe COVID-19 during two waves of the pandemic (2020/21 vs. 2021/22). A total of 101 patients from the 2021/22 wave were compared with 101 sex- and age-matched subjects from the 2020/21 wave. Patients from both groups were hospitalized during the winter season from 1 December to 28 February. Men and women were analyzed together and separately. The mean 25(OH)D concentration increased from 17.8 ± 9.7 ng/mL to 25.2 ± 12.6 ng/mL between waves. The prevalence of vitamin D deficiency (30 ng/mL) increased from 10% to 34% (p < 0.0001). The proportion of patients with a history of vitamin D supplementation increased from 18% to 44% (p < 0.0001). Low serum 25(OH)D concentration was independently associated with mortality after adjusting for age and sex for the whole cohort of patients (p < 0.0001). The prevalence of inadequate vitamin D status in hospitalized patients with COVID-19 in Slovakia decreased significantly, probably due to a higher rate of vitamin D supplementation during the COVID-19 pandemic.

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.