In this review, we discuss the main reasons for the vitamin D insufficiency in Russian Federation, as well as data on the prevalence of vitamin D deficiency among various population groups and regions, which confirm the widespread prevalence of vitamin D deficiency in the country. The discussed data suggest that the current vitamin D insufficiency in Russian population (reduced levels of 25(OH)D occurs in 50 - 94% of general population) is due to both a low level of its endogenous synthesis and insufficient intake from food : the territory of the country is located in a zone of low insolation, and at the same time, the main natural sources of vitamin D (sea fish of fatty varieties) and fortified with vitamin D products are very limited in the diet of the population. Taking measures to improve the status of vitamin D and maintaining the optimal serum levels of 25(OH)D in children and adults, adequate vitamin D intake will improve the condition of the musculoskeletal system, as well as reduce the risk of development and improve the control of some chronic diseases.

This draft clinical practice guideline for the diagnosis, treatment and prevention of vitamin D deficiency is an update from a previous 2016 document. An analysis of the relevant literature data was carried out, with particular attention to meta-­analyzes, randomized clinical trials and systematic reviews published over the past 5 years. The updated recommendations were discussed and revised by the leading endocrinologists of the Russian Federation, who have expert status in this issue.The classification of 25(OH)D levels has been revised (in particular, the target range of 25(OH)D values has been specified), recommendations have been developed for screening of the disorders associated with vitamin D deficiency. The concept of vitamin D-associated toxicity and recommendations for its diagnosis and prevention have been introduced. Also, indications for the assessment of other vitamin D metabolites besides 25(OH)D, the main marker of vitamin D status, have been indicated.The section regarding treatment of vitamin D deficiency has been expanded and corrected. The major additions concerned the replenishment of the vitamin D deficiency and insufficiency in certain categories of patients (particularly, in the presence of the chronic kidney disease and autoimmune diseases, as well as in pregnant women) and monitoring of the effectiveness and safety of the therapy. The indications for prescribing active metabolites of vitamin D have been adjusted. Recommendations for the prevention of vitamin D deficiency in the general population have also been revised, taking into account large randomized clinical trials, meta-analyzes and systematic reviews of recent years.This publication is an expanded version of the federal guidelines.

Since the discovery of vitamin D, interest in role of vitamin D in human body is consistently growing, and there is increasing evidence that vitamin D is not only essential to bone health but may also be involved in physiology of many other tissues. Thus understanding of its aspects in particular tissues appears to be important because of possible contribution to pathophysiologic processes. Intracrine regulatory systems associated with widely expressed vitamin D metabolizing enzymes, ways of cellular intake and signal pathways involved are of particular interest. Association of local effects with vitamin D level in blood is under investigation on animal models as well as in clinical studies; values of vitamin D level that mediate extraskeletal effects should be determined. In this review, we discuss impact of vitamin D on immune function and its association with skin, nervous system, cardiovascular system, obesity and diabetes mellitus, cancer, reproductive function, prevention of falls and quality of life improvement.

Background. A vitamin D deficiency is a global wide health problem. Inadequate vitamin D status leads to serious medical, social and economic consequences and requires timely diagnosis and adequate correction.Aim: to assess the incidence of vitamin D deficiency among the population living in regions of the Russian Federation located at latitudes from 45° to 70° and to study its relationship to various factors (demographic, socio-economic, geographical, etc.).Materials and methods. A multicenter, cross-sectional, randomized study of individuals of both sexes aged 18 to 50 years. The study of 25ОНD level in the blood serum was carried out by INVITRO LLC laboratories using chemilumescent analysis in two stages: in the period from March to May 2020 and from October to November 2020. The first stage of the study involved 500 volunteers (77% women, 23% men). Demographic and socioeconomic characteristics, factors associated with vitamin D levels, were assessed using a specially designed questionnaire.Results. In this article we present the results of the first stage. A countrywide high prevalence of vitamin D deficiency (56.4%) and insufficiency (27.9%) was revealed, that is, 84.3% of the population aged 18–50 years requires cholecalciferol supplementation. The lowest vitamin D status was found in St. Petersburg, Arkhangelsk, Kyzyl and Rostov-on-Don (over 90% of participants had inadequate levels). A decrease in the level of 25ОНD was observed to a greater extent in men than in women (p <0.05), as well as in young people aged 18–25 years (p <0.05). No major association of vitamin D status with anthropometric parameters, the number of days of disability, were not found. However, those who went to tanning beds or were in direct sunlight for at least 30 days a year had higher levels of 25ОНD, and those using sunscreens had lower levels.Conclusion. The data obtained confirms the widespread prevalence of vitamin D deficiency and insufficiency in the country (84.3% of participants), generally not related to the geographical latitude of residence, which indicates the need for vitamin D supplementation in a significant part of the population.

There is increasing data regarding the association between vitamin D and COVID-19. This study aimed to reveal the alterations of vitamin D metabolism in the setting of COVID-19. We examined 119 adult COVID-19 inpatients and 44 apparently healthy adult individuals with similar serum 25OH-D₃ levels as a reference group. The assessment included serum biochemical parameters (total calcium, albumin, phosphorus, creatinine), parathyroid hormone (PTH), vitamin D-binding protein (DBP), vitamin D metabolites (25OH-D₃, 25OH-D₂, 1,25(OH)₂D₃, 3-epi-25OH-D₃, 24,25(OH)₂D₃ and D₃) and free 25OH-D. COVID-19 patients had in general very low vitamin D levels (median 25OH-D₃ equals 10.8 ng/mL), accompanied by an increased production of the active vitamin D metabolite (1,25(OH)₂D₃), estimated as higher 1,25(OH)₂D₃ serum levels (61 [44; 81] vs. 40 [35; 50] pg/mL, p < 0.001) and lower 25OH-D₃/1,25(OH)₂D₃ ratio (175 [112; 260] vs. 272 [200; 433], p < 0.001) which is presumably aimed at preventing hypocalcemia. Patients with COVID-19 also had elevated DBP (450 [386; 515] vs. 392 [311; 433] mg/L, p < 0.001) and low free 25OH-D levels (<LoB vs. 3.9 [3.2; 4.4] pg/mL, p < 0.001). Follow-up assessment of the COVID-19 inpatients showed recovery of the observed changes. Overall, hospitalized patients with an acute course of COVID-19 have not only very low levels of 25OH-D but also profound abnormalities in the metabolism of vitamin D regardless of the clinical course of the disease. These alterations might exacerbate existing vitamin D deficiency and its negative impact.

In this prospective controlled study, we examined 25 adults with adequately controlled (HbA1c level < 8.0%) type 1 diabetes mellitus (T1DM) and 49 conditionally healthy adults, intending to reveal the diversity of vitamin D metabolism in the setting of cholecalciferol intake at a therapeutic dose. All patients received a single dose (150,000 IU) of cholecalciferol aqueous solution orally. Laboratory assessments including serum vitamin D metabolites (25(OH)D₃, 25(OH)D₂, 1,25(OH)₂D₃, 3-epi-25(OH)D₃ and 24,25(OH)₂D₃), free 25(OH)D, vitamin D-binding protein (DBP) and parathyroid hormone (PTH) as well as serum and urine biochemical parameters were performed before the intake and on Days 1, 3 and 7 after the administration. The studied groups had no significant differences in baseline parameters except that the patients with diabetes showed higher baseline levels of free 25(OH)D (p < 0.05). They also lacked a correlation between the measured and calculated free 25(OH)D in contrast to the patients from the control group (r = 0.41, p > 0.05 vs. r = 0.88, p < 0.05), possibly due to the glycosylation of binding proteins, which affects the affinity constant for 25(OH)D. The elevation of vitamin D levels after the administration of cholecalciferol was comparable in both groups, with slightly higher 25(OH)D₃ levels observed in the diabetes group throughout the study since Day 1 (p < 0.05). Overall, our data indicate that in patients with adequately controlled T1DM 25(OH)D₃ levels and the therapeutic response to cholecalciferol is similar to that in healthy individuals.