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Recent studies showed that a low 25-hydroxyvitamin D (25(OH)D) level was associated with a higher risk of morbidity and severe course of COVID-19. Our study aimed to evaluate the effects of cholecalciferol supplementation on the clinical features and inflammatory markers in patients with COVID-19. A serum 25(OH)D level was determined in 311 COVID-19 patients. Among them, 129 patients were then randomized into two groups with similar concomitant medication. Group I (n = 56) received a bolus of cholecalciferol at a dose of 50,000 IU on the first and the eighth days of hospitalization. Patients from Group II (n = 54) did not receive the supplementation. We found significant differences between groups with the preferential increase in serum 25(OH)D level and Δ 25(OH)D in Group I on the ninth day of hospitalization (p < 0.001). The serum 25(OH)D level on the ninth day was negatively associated with the number of bed days (r = −0.23, p = 0.006); we did not observe other clinical benefits in patients receiving an oral bolus of cholecalciferol. Moreover, in Group I, neutrophil and lymphocyte counts were significantly higher (p = 0.04; p = 0.02), while the C-reactive protein level was significantly lower on the ninth day of hospitalization (p = 0.02). Patients with supplementation of 100,000 IU of cholecalciferol, compared to those without supplementation, showed a decrease in the frequencies of CD38++CD27 transitional and CD27−CD38+ mature naive B cells (p = 0.006 and p = 0.02) and an increase in the level of CD27−CD38− DN B cells (p = 0.02). Thus, the rise in serum 25(OH)D level caused by vitamin D supplementation in vitamin D insufficient and deficient patients may positively affect immune status and hence the course of COVID-19.

Several meta-analyses found an association between low maternal serum 25-hydroxyvitamin D (25(OH)D) level and gestational diabetes mellitus (GDM). However, some of them reported significant heterogeneity. We examined the association of serum 25(OH)D concentration measured in the first and in the second halves of pregnancy with the development of GDM in Russian women surveyed in the periods of 2012−2014 and 2018−2021. We conducted a case−control study (including 318 pregnant women) nested on two previous studies. In 2012−2014, a total of 214 women (83 GDM and 131 controls) were enrolled before 15 weeks of gestation and maternal serum 25(OH)D concentrations were measured twice: at 8th−14th week of gestation and simultaneously with two-hour 75 g oral glucose tolerance test (OGTT) at 24th−32nd week of gestation. In the period of 2018−2021, 104 women (56 GDM and 48 controls) were included after OGTT and 25(OH)D concentrations were measured at 24th−32nd week of gestation. Median 25(OH)D levels were 20.0 [15.1−25.7] vs. 20.5 [14.5−27.5] ng/mL (p = 0.565) in GDM and control group in the first half of pregnancy and 25.3 [19.8−33.0] vs. 26.7 [20.8−36.8] ng/mL (p = 0.471) in the second half of pregnancy, respectively. The prevalence rates for vitamin D deficiency (25(OH)D levels < 20 ng/mL) were 49.4% and 45.8% (p = 0.608) in the first half of pregnancy and 26.2% vs. 22.1% (p = 0.516) in the second half of pregnancy in women who developed GDM and in women without GDM, respectively. The frequency of vitamin D supplements intake during pregnancy increased in 2018−2021 compared to 2012−2014 (p = 0.001). However, the third trimester 25(OH)D levels and prevalence of vitamin D deficiency (25.5 vs. 23.1, p = 0.744) did not differ in women examined in the periods of 2012−2014 and 2018−2021. To conclude, there was no association between gestational diabetes risk and maternal 25(OH)D measured both in the first and in the second halves of pregnancy. The increased prevalence of vitamin D supplements intake during pregnancy by 2018−2021 did not lead to higher levels of 25(OH)D.

Aim: To assess the incidence of vitamin D deficiency and insufficiency among the adult population living in the regions of the Russian Federation located at latitudes from 45 to 70., Materials and Methods: Russian multicenter non-interventional registry study using the "cross-sectional" method., Results: In this study, 72.1% of the examined have the status of vitamin D deficiency and insufficiency, while an adequate level was diagnosed in 27.8% of cases. When assessing the degree of vitamin D deficiency depending on the season, statistically significant differences (p0.00001) were found between the periods: vitamin D deficiency or insufficiency was observed in 84.2% of autumn and in 62.4% of spring. The highest incidence of vitamin D deficiency and insufficiency was recorded in males compared with females (p=0.013, 79 and 70.3% respectively). Vitamin D deficiency is observed in young people in the age subgroup of 1825 years (p0.001, 54% in the study as a whole) much more often than in older people Conclusion. The widespread high prevalence of vitamin D deficiency in the Russian Federation is not related to geographic region of residence, but to some extent depends on the season. The high-risk group for vitamin D deficiency and insufficiency is young men. The significant role of vitamin D in the human body justifies the need to supplement and clarify a single concept for the prevention, diagnosis and treatment of conditions associated with deficiency, so higher implementation of National Clinical Guidelines is needed.

Background: The association between vitamin D deficiency and the severity of COVID-19 is currently being actively discussed around the world., Aim: The aim of this study was to assess the prevalence of vitamin D insufficiency and deficiency and compare it with the incidence rates of SARS-CoV-2 in eight Federal Districts of the Russian Federation., Materials and Methods: We included 304,564 patients (234,716 women; 77,1%) with serum 25(OH)D levels results performed September 2019 through October 2020., Results: Only 112,877 people (37.1%) had a normal serum 25(OH)D level, others had a deficiency. Vitamin D insufficiency and deficiency was presented with the same frequency in women and men, and no differences were found depending on the geographical location and age in subjects from 18 to 74 years old. However, subjects over 75 years more often had vitamin D deficiency, while subjects under 18 years had normal levels in over 50% cases. In addition, 21,506 patients were tested for SARS-CoV-2 by PCR with further comparison of results with serum 25(OH)D level. The SARS-CoV-2 positivity rate was detected in 3,193 subjects, negative in 18,313. There were no differences in the morbidity in a vitamin D deficiency and a normal level. Thus, 14.8% subjects had positive PCR rates among vitamin D deficiency patients (4,978 tests), 14.9% when 25(OD)D level was from 20 to 30 ng/ml (7,542 tests), 15.0% among those who had 25(OH)D 30- 50 ng/ml (6,622 tests), and 13.9% when vitamin D was more than 50 ng/ml (4,612 tests)., Conclusion: There was no association between the COVID-19 incidence and vitamin D status in different regions of Russia. Although the nutrient deficiency persists in all regions and is most often diagnosed in people over 75 years old.

We evaluated associations between serum 25-hydroxyvitamin D [25(OH)D] level and severity of new coronavirus infection (COVID-19) in hospitalized patients. We assessed serum 25(OH)D level in 133 patients aged 21-93 years. Twenty-five (19%) patients had severe disease, 108 patients (81%) had moderate disease, and 18 (14%) patients died. 25(OH)D level ranged from 3.0 to 97.0 ng/mL (median, 13.5 [25%; 75%, 9.6; 23.3] ng/mL). Vitamin D deficiency was diagnosed in 90 patients, including 37 with severe deficiency. In patients with severe course of disease, 25(OH)D level was lower (median, 9.7 [25%; 75%, 6.0; 14.9] ng/mL), and vitamin D deficiency was more common than in patients with moderate course (median, 14.6 [25%; 75%, 10.6; 24.4] ng/mL, p = 0.003). In patients who died, 25(OH)D was 9.6 [25%; 75%, 6.0; 11.5] ng/mL, compared with 14.8 [25%; 75%, 10.1; 24.3] ng/mL in discharged patients ( p = 0.001). Severe vitamin D deficiency was associated with increased risk of COVID-19 severity and fatal outcome. The threshold for 25(OH)D level associated with increased risk of severe course was 11.7 ng/mL. Approximately the same 25(OH)D level, 10.9 ng/mL, was associated with increased risk of mortality. Thus, most COVID-19 patients have vitamin D deficiency; severe vitamin D deficiency is associated with increased risk of COVID-19 severity and fatal outcome.