Introduction: All epidemiological studies suggest that vitamin D deficiency is prevalent among the Polish general population. Since vitamin D deficiency was shown to be among the risk factors for many diseases and for all-cause mortality, concern about this problem led us to update the previous Polish recommendations. Methods: After reviewing the epidemiological evidence, case-control studies and randomized control trials (RCTs), a Polish multidisciplinary group formulated questions on the recommendations for prophylaxis and treatment of vitamin D deficiency both for the general population and for the risk groups of patients. The scientific evidence of pleiotropic effects of vitamin D as well as the results of panelists’ voting were reviewed and discussed. Thirty-four authors representing different areas of expertise prepared position statements. The consensus group, representing eight Polish/international medical societies and eight national specialist consultants, prepared the final Polish recommendations. Results: Based on networking discussions, the ranges of total serum 25-hydroxyvitamin D concentration indicating vitamin D deficiency [<20 ng/mL (<50 nmol/L)], suboptimal status [20–30 ng/mL (50–75 nmol/L)], and optimal concentration [30–50 ng/mL (75–125 nmol/L)] were confirmed. Practical guidelines for cholecalciferol (vitamin D₃) as the first choice for prophylaxis and treatment of vitamin D deficiency were developed. Calcifediol dosing as the second choice for preventing and treating vitamin D deficiency was introduced. Conclusions: Improving the vitamin D status of the general population and treatment of risk groups of patients must be again announced as healthcare policy to reduce a risk of spectrum of diseases. This paper offers consensus statements on prophylaxis and treatment strategies for vitamin D deficiency in Poland.

Idiopathic infantile hypercalcemia (IIH) is a mineral metabolism disorder characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. The periodical increase in incidence of IIH, which occurred in the twentieth century in the United Kingdom, Poland, and West Germany, turned out to be a side effect of rickets over-prophylaxis. It was recently discovered that the condition is linked to two genes, CYP24A1 and SLC34A1. The aim of the study was to search for pathogenic variants of the genes in adult persons who were shortlisted in infancy as IIH caused by “hypersensitivity to vit. D”. All persons were found to carry mutations in CYP24A1 or SLC34A1, nine and two persons respectively. The changes were biallelic, with one exception. Incidence of IIH in Polish population estimated on the basis of allele frequency of recurrent p.R396W CYP24A1 variant, is 1:32,465 births. It indicates that at least a thousand homozygotes and compound heterozygotes with risk of IIH live in the country. Differences in mechanism of developing hypercalcemia indicate that its prevention may vary in both IIH defects. Theoretically, vit. D restriction is a first indication for CYP24A1 defect (which disturbs 1,25(OH)₂D degradation) and phosphate supplementation for SLC34A1 defect (which impairs renal phosphate transport). In conclusion, we suggest that molecular testing for CYP24A1 and SLC34A1 mutations should be performed in each case of idiopathic hypercalcemia/hypercalciuria, both in children and adults, to determine the proper way for acute treatment and complications prevention.

Introduction: Local and international guidelines have provided schedules for the vitamin D supplementation of general populations of different ages, including children. Our study aimed to assess 25(OH)D concentration and its potential change during a growth and maturation period, adding parameters that reflect the risk of hypercalcemia. Materials and methods: The available 25(OH)D concentration values (n = 17,636; 7.8 ± 6.0 years), calcium (n = 2673; 16.3 ± 6.1 years) and phosphate (n = 2830; 3.8 ± 5.2 years) metabolism markers were analyzed in a studied group of patients (0–18 years). Results: In the studied group the mean 25(OH)D concentration was 29.4 ± 11.7 ng/mL. Concentrations of 25(OH)D < 10 ng/mL were observed in 1.7% of patients (n = 292), 10–20 ng/mL in 17.2% (n = 3039), 20–30 ng/mL in 39.5% (n = 6960) and 30–50 ng/mL in 37.2% (n = 6567). In patients with a 25(OH)D concentration <10 ng/mL, normal calcemia (2.25–2.65 mmol/L) was observed in 29.5% of cases (n = 86). Three patients had 25(OH)D concentrations above 100 ng/mL with co-existing hypercalcemia; the mean was Ca = 3.40 mmol/L. Hypocalcemia (Ca < 2.25 mmol/L) was observed in 10,4% of patients (n = 2797). Furthermore, 5.0% of patients showed an increased calcium concentration >2.65 mmol/L (n = 1327). The highest mean 25(OH)D concentration of 32.1 ng/mL ± 12.9 was noted in the years 2018–2019 (n = 3931) and the lowest in the year 2015 (27.2 ng/mL ± 11.0; n = 2822). Conclusions: Vitamin D deficiency (<20 ng/mL) was noted in 18,9% of subjects in the years 2014–2019. An effective prevention of vitamin D deficiency was observed in children aged 3 years and younger. A relationship between the concentrations of calcium and 25(OH)D was not observed.

Background: The least significant change (LSC) method should be introduced and considered a proper method to define the smallest clinically important difference between two consecutive measurements. Methods: The LSC was calculated based on 150 patients, with a total 25-hydroxyvitamin D [25(OH)D] IDS-iSYS assay performed in triplicate. The LSC was determined by multiplying the calculated root mean square precision error by a factor of 2.77. The study group was additionally divided into subgroups according to gender, age, serum 25(OH)D concentration, and date of assays. Results: The LSC was 4.0 ng/mL (13.2%) for the entire group (n = 150; 450 assays) and was not dependent on gender, age of patients, or the date of assays (p > 0.05). The LSC value depended only on the 25(OH)D concentration value. In the subgroup with vitamin D deficiency (<20 ng/mL), the obtained LSC value was 2.2 ng/mL (14.7%), which was lower compared to all other groups (p < 0.05 for insufficiency, and p < 0.0001 for the optimal concentration value). In the subgroup with 25(OH)D concentrations >50 ng/mL (n = 4; 12 assays), the calculated LSC was 11.8 ng/mL (16.9%) and differed statistically only from the subgroup with vitamin D deficiency (p < 0.005). Conclusions: An absolute LSC of 4.0 ng/mL was calculated for the IDS-iSYS assay used in our study and should be considered when two (or more) assay results of 25(OH)D performed for a single patient are compared.

Background: The Least Significant Change (LSC) should be introduced and considered as a proper method to define the smallest clinically important difference between two consecutive measurements. Methods: The LSC was calculated based on 150 patients with a total 25-hydroxyvitamin D [25(OH)D] IDS-iSYS assay performed in triplicate. The LSC was determined by multiplying the calculated precision error by a factor of 2,77. The study group was additionally divided into subgroups according to gender, age, serum 25(OH)D concentration, and date of assays. Results: The LSC was 4,0 ng/ml (13,2%) for the entire group (n=150; 450 assays) and was not dependent on gender, age of patients or the date of assays (p>0.05). The LSC value depended only on the 25(OH)D concentration value. In the subgroup with vitamin D deficiency (< 20 ng/ml), the obtained LSC value was 2.2 ng/ml (14.7%) and was lower compared to all other groups (p< 0.05 for insufficiency, and p< 0.0001 for optimal concentration value). In the subgroup with 25(OH)D concentration >50 ng/ml (n=4; 12 assays), the calculated LSC was 11.8 ng/ml (16.9%) and differed statistically only from the subgroup with vitamin D deficiency (p< 0.005). Conclusion: An absolute LSC of 4.0 ng/ml was calculated for the IDS-iSYS assay used in our study, and should be considered when two (or more) assay results of 25(OH)D performed for a single patient are compared.