Abstract
Vitamin D (VitD) has a critical role in phosphorous–calcium metabolism as well as an important role in the immune system. In the human body, VitD is synthesized as cholecalciferol in the skin, but this process requires sunlight (UVB) radiation. Numerous reports showed high prevalence of VitD deficiency, particularly during the winter season, indicating the importance of VitD supplementation. Various factors can affect the absorption of VitD, including dosage and formulation. The primary study objective was to examine the efficiency of supplementation with three different formulations containing cholecalciferol in comparison with the control group. The secondary objective was to identify other factors affecting increase in serum 25-OH-VitD. A randomized controlled intervention study was conducted in Slovenia during wintertime (January– March) on 105 apparently healthy subjects (aged 18–65 years) with suboptimal VitD status (25-OH-VitD 30–50 nmol/L). Subjects were randomized into four groups: three treatment groups receiving (A) capsules with starch-adsorbed VitD, (B) oil-based Valens VitD oral spray, or (C) water-based Valens VitD oral spray and a control group (D) which did not receive supplemental VitD. Two months of supplementation with cholecalciferol (1000 IU; 25 µg daily) resulted in significant increase in serum 25-OH-VitD levels in comparison with control group (pooled Δc 32.8 nmol/L; 95% CI: 23.0, 42.5, p < 0.0001). While we did not observe any significant differences between the tested formulations, the efficiency of supplementation was associated with body mass index and baseline serum 25-OH-VitD level. Higher supplementation efficiency was observed in participants with normal body weight (BMI < 25) and in those with more pronounced VitD insufficiency. We also determined that tested dosage was not sufficient to achieve recommended 25-OH-VitD levels in all subjects.
Highlights
Vitamin D is a prohormone with various functions in the human body
All three tested vitamin D formulations were efficient in improving suboptimal vitamin D status; two months of treatment with 25 μg (1000 IU) daily was not sufficient to assure recommended serum 25-OH-vitD levels in all subjects
We determined that efficiency of vitamin D supplementation is associated with baseline serum 25-hydroxyvitamin D concentration
Summary
Vitamin D is a prohormone with various functions in the human body. Sufficient vitamin D levels are essential to support musculoskeletal health and a range of other conditions. It is well established that vitamin D deficiency is a worldwide problem [3], present both in developed and less developed countries. Vitamin D in the body originates from both biosynthesis in Nutrients 2020, 12, 1268; doi:10.3390/nu12051268 www.mdpi.com/journal/nutrients. Nutrients 2020, 12, 1268 the skin triggered by ultraviolet B (UVB) irradiation as well as dietary sources. Rather than diet, has been reported as the main source for the majority of the population, while in the absence of sufficient sun exposure, vitamin D becomes an essential nutrient [4,5]. UVB radiation initiates vitamin D3 synthesis through the conversion of 7-dehydrocholesterol (7-DHC) to previtamin D3. A heat isomerization of previtamin D3 to cholecalciferol (vitamin D3) is followed by hydroxylation in the liver to 25-hydroxyvitamin D (25-OH-VitD) and further in kidney to the active form of the vitamin 1,25-dihydroxyvitamin D3 (1,25-OH-VitD) [6]
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