Introduction
Obesity is considered one of the independent factors of the severity of the SARS-CoV-2 infection1. Excessive body mass index (BMI), together with older age and male sex, were found to be crucial factors in calculating the odds ratio of the severe course of COVID-192. Among these, vitamin D was considered another important factor due to its well-known immunological properties. Based on the first meta-analyses of the COVID-19 pandemic, a conclusion was drawn that deficiency of vitamin D, commonly reported, might be associated with a worse prognosis3,4. Moreover, some studies indicate that the SARS-CoV-2 positive rate is associated with the 25-hydroxyvitamin [25(OH)D] levels5. However, cholecalciferol supplementation has not been linked to the risk of infection and their severity6. Indeed, subjects infected with SARS-CoV-2 demonstrated severe deficit in 25(OH)D, leading to substantial comorbidities7.
In accordance, most recent analyses of randomized clinical trials suggested that vitamin D deficiency, despite its beneficial influence on health, did not have as crucial a role as expected in conditions including: asthma, cardiovascular or autoimmune diseases, and cancer8. Revision of numerous papers within previous years indicated that, besides being a potential cause of certain diseases’ prevalence, low vitamin D levels could be a consequence of the ongoing inflammatory process, with huge heterogeneity depending on the time-point of the observations9, 10–11. In addition, even other microelements like magnesium can substantially affect 25(OH)D concentration, thus requiring proper optimization to establish the actual status of the vitamin12.
In the course of SARS-CoV-2 infection, 25(OH)D deficiency was attributed to an increased predisposition to develop symptomatic infection, higher risk of ARDS (acute respiratory distress syndrome) requiring hospitalization in the ICU (intensive care unit), and increased mortality. Those observations were predominant in the group of patients with older age, institutionalized, and obese13. El-Saber Batiha et al. highlighted also the potential immunomodulatory role of low doses of steroids in mitigating the severity of SARS-CoV-2 infection, particularly through its effects on inflammatory responses and cytokine regulation14. In relation to the respiratory tract, patients with frequent infections were shown to benefit from regular supplementation of the recommended 4000 IU/d of vitamin D, significantly reducing infection probability score (IPS) and antibiotics use and improving overall well-being15,16. The data collected to date demonstrate substantial heterogeneity associated, inter alia, with different study groups, stages of the infection, and therapeutic approaches implemented17, 18, 19, 20–21. That also refers to the different ways of vitamin D supplementation, with more significance attributed to regular maintenance of the vitamin status than adjunct therapeutic after infection with SARS-CoV-222,23. Therefore, no unambiguous results indicate the completely beneficial role of vitamin D in the course of SARS-CoV-2 infection. Given the continued uncertainty and conflicting findings, our study aimed to assess the level of 25(OH)D in hospitalized SARS-CoV-2-infected patients and to establish their potential association with the clinical presentation and laboratory parameters, particularly those related to immune and inflammatory responses.
Results
Evaluation of 25(OH)D levels in plasma of patients infected with SARS-CoV-2
The cumulative concentration of 25-hydroxyvitamin D in the studied group was found to demonstrate signs of severe deficiency with a median of 4.10 nmol/L. We did not report gender-related differences in 25(OH)D levels. The season of the patient’s admission was also irrelevant in the context of 25(OH)D concentration. Patients above 70 years old are reported for a slight tendency for higher levels of 25(OH)D compared to the group aged at 45–70 years (p = 0.0945). The severity of patients’ condition was not associated with differences in 25(OH)D concentrations in plasma. However, extended hospitalization was accompanied by lower values of that parameter (1–2 weeks: p = 0.0453, > 2 weeks: p = 0.0404, compared to the group of maximum 1-week hospitalization) (Table 1). In addition, we analyzed whether the distribution of patients with lower/higher values of 25(OH)D (based on the median value within all patients) is different in different groups. In accordance, such variations were not reported in the context of sex, age and disease severity. However, in the context of hospitalization time, we found that groups requiring less than a week of therapy demonstrated a significantly lower share of subjects with more pronounced 25(OH)D deficiency compared to those with extended treatment (Fig. 1).
Table 1. 25-hydroxyvitamin D [25(OH)D] assessment in plasma. Concentration of 25(OH)D23 shown in groups established based on sex, season, age, disease severity, and hospitalization time. Data presented as medians with 25th and 75th quartiles in the brackets.
25-hydroxyvitamin D [25(OH)D] concentrations in plasma50 | ||||
|---|---|---|---|---|
4.10 (2.78; 5.37) | ||||
Sex | ||||
Female (n = 71) | Male (n = 70) | p value | ||
4.23 (3.13; 5.59) | 3.82 (2.06; 5.20) | 0.1712 | ||
Season | ||||
Spring/Summer (n = 48) | Autumn/Winter (n = 93) | p value | ||
3.32 (2.02; 4.75) | 3.92 (2.61; 5.15) | 0.1824 | ||
Age | ||||
20–45 years (n = 46) | 45–70 years (n = 69) | > 70 years (n = 26) | p value | |
4.13 (2.89; 5.54) | 3.72 (2.21; 4.90) | 4.79 (3.20; 5.90) | 0.3951 | |
Disease severity | ||||
Low (n = 46) | Moderate (n = 50) | High (n = 45) | p value | |
4.43 (2.80; 6.20) | 3.85 (2.24; 5.32) | 3.98 (3.13; 5.55) | 0.4695 | |
Hospitalization time | ||||
< 1 week (n = 33) | 1–2 weeks (n = 62) | > 2 weeks (n = 46) | p value | |
4.52 (3.61; 6.31) | 3.67 (2.11; 5.08) | 3.72 (2.11; 4.94) | 0.0342 | |
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Fig. 1
Distribution of patients within groups with lower or higher levels of 25(OH)D (below/above median value). Differences in the frequency of subjects with lower/higher values of the vitamin were demonstrated within groups stratified based on sex (A), age (B), disease severity (C), and hospitalization time (D).
Association between plasma 25(OH)D and SARS-CoV-2 -related genes in infected patients
Stratification of patients into groups based on sex, age, disease severity, and 25(OH)D level was used to evaluate vitamin D3 relation to genes used in SARS-CoV-2 diagnostics. First, the tested vitamin demonstrated a tendency for negative correlation with ORF1ab gene (spike protein gene) in males (p = 0.0927) and in the total group of patients (p = 0.0678). The most significant association between 25(OH)D and ORF1ab gene was found in patients aged 45–70 years (p = 0.0052). Surprisingly, in that group, a negative moderate correlation indicates that lower values of the vitamin are followed by higher ct values of the tested gene—meaning lower expression of SARS-CoV-2 genes. Similar correlation was found in reference to the high disease severity group (p = 0.0276). Regarding hospitalization time, for those treated for more than 2 weeks, a moderate negative correlation of 25(OH)D with ORF1ab was also demonstrated (p = 0.0090). Interestingly, no statistically significant associations were shown between 25(OH)D plasma concentration and other routinely used genes—N and E (nucleocapsid and envelope protein gene, respectively) (Fig. 2).
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Fig. 2
Correlation of 25(OH)D with SARS-CoV-2-related genes with patients’ stratification. Data presented as r values and significance indicated by exact p-value or asterisks: p < 0.05-*, p < 0.01-**, p < 0.001-***.
Assessment of 25(OH)D concentrations influences on relative risk of infection progression
Patients with SARS-CoV-2 infection were divided into two groups based on the median value of plasma 25(OH)D concentration (4.10 nmol/L) for those with lower and higher values. Next, the Fishers’ test was implemented to establish the relative risk of selected parameters or outcomes occurrence depending on the plasma 25(OH)D levels. As demonstrated below, in the studied group of patients, lower values of 25-hydroxyvitamin D did not influence the prevalence of selected symptoms of the infection; the same results were observed in reference to the disease severity, hospitalization duration, or expression of SARS-CoV-2 genes (Fig. 3).
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Fig. 3
Relative risk analysis of 25(OH)D levels influence the occurrence of the disease symptoms, se-verity, hospitalization time, and SARS-CoV-2 gene expression. Data was presented as a summary relative risk values graph and a tabular demonstration of the prevalence of selected outcomes with exact risk values and p values.
25(OH)D association with laboratory parameters of SARS-CoV-2 patients
When analyzing links between already reduced levels of 25(OH)D and routine laboratory data, we found a positive moderate correlation with the INR ratio. No other associations have been demonstrated in the total group of patients. Subsequently, we stratified patients into groups based on hospitalization duration or viral expression. In the context of hospitalization, the tendency for a positive correlation with INR ratio was only shown in subjects treated for more than 2 weeks. When evaluating 25(OH)D contribution depending on viral level, we observed even more pronounced positive correlations with D-dimer levels in patients with higher expression of viral genes. Concomitantly, in the same subgroup, 25(OH)D demonstrated a negative moderate correlation with hemoglobin concentration. Interestingly, a positive correlation with the INR ratio was only shown in those infected patients with lower viral expression (Fig. 4.).
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Fig. 4
Association of 25(OH)D with laboratory parameters of SARS-CoV-2-infected, and with stratification based on hospitalization time and viral expression. Data presented as r values and significance indicated by exact p-value or asterisks: p < 0.05-*, p < 0.01-**, p < 0.001-***.
Assessment of 25(OH)D concentrations influences the relative risk of changes in laboratory data
Finally, we implemented risk analysis to establish 25-hydroxyvitamin D levels’ influence on the chances of the occurrence of selected laboratory parameters. No significant relations were demonstrated regarding hemostasis-related parameters, namely PLT, INR, fibrinogen, and D-dimer. In addition, 25(OH)D levels did not affect oxygen saturation measurements. Despite the lack of significant results in the context of tested vitamin levels and Hb concentration, we found that lower plasma 25-hydroxyvitamin D concentrations are associated with a doubled risk of elevated ferritin levels when compared to higher vitamin D patients’ group (p = 0.0208). Furthermore, we showed a 2.17-fold increased risk of elevated leukocyte levels (WBC) in patients with lower plasma 25-hydroxyvitamin D concentrations, indicating a significant association between vitamin D status and leukocyte count (p = 0.0340). Interestingly, the only leukocyte population demonstrating corresponding risk analysis results were neutrophils (NEUT [%]); however, no significance level was reached (p = 0.0826). (Fig. 5).
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Fig. 5
Relative risk analysis of 25(OH)D levels influences the occurrence of the specific levels of the selected laboratory parameters. Data was presented as a summary relative risk values graph and a tabular demonstration of the prevalence of selected outcomes with exact risk values and p values.
Discussion
Vitamin D is one of the most substantial micronutrients, among zinc or vitamin C, with an advantageous influence on patients’ condition in the course of infection-related inflammation of the respiratory tract, with lesser risk and reduced duration of symptoms24. Results of numerous studies from both pediatric and adolescent subjects indicated a critical prevalence of vitamin D deficiency among those infected with SARS-CoV-2. In addition, suggesting that compounds play a preventive role in the severity of that condition7,25. Our study allowed us to reveal the severity of the vitamin D deficiency within population of infected patients at the time of the COVID-19 pandemic, with further investigation of its role in the infection outcome.
Blood concentration of vitamin D was shown to be associated with season-related changes in UV exposure, higher in summertime versus low levels in winter and autumn26. During the SARS-CoV-2 pandemic, home isolation, reduced outdoor activity, UV exposure blocked by clothes, and the infection itself (often repeatedly occurring) significantly affected vitamin D availability27,28. We showed that all of our infected patients’ 25(OH)D levels oscillated around values typical for severe deficiency of that compound. And that is no isolated case, as comparable levels were shown even in groups narrowed to asymptomatic/mild asymptomatic individuals4,29. Those data seemed to be supported by prolonged viral exposure and the fact of commonly occurring deficiencies in Eastern European countries, with around 80% of subjects in Poland around the August/September period30. Additionally, dietary habits with low intake of vitamin D-rich products (fatty fish) further affect low synthesis of that compound31,32. No influence of sex, age, or even year’s season was demonstrated in reference to the vitamin concentrations during the spread of COVID-19. No significant differences were registered despite slightly lower values in moderate and high-risk infected subjects. Previous studies actually showed that vitamin D levels might influence severity in the infected subjects, but at the same time, they indicated a huge heterogeneity in those observations11,33. Furthermore, considering other studies, even regular supplementation (with 5000 IU/d) might not be efficient for long-term improvement of vitamin D status in patients and healthy controls, as shown in soccer players during the pandemic27. Similarly, the high single dose of vitamin D3 (200.000 IU) applied in COVID-19-infected patients from the moderate/severe group showed no benefits for hospitalization duration, ICU admission, or mortality34,35.
Research conducted in the course of the SARS-CoV-2-related crisis suggested significant benefits of higher vitamin D levels and its supplementation in subjects with mild and severe conditions, affecting inter alia hospitalization time and better therapeutic outcomes10,19,36. In fact, our study revealed that extended hospitalization time was associated with 25(OH)D deficiency and generally higher frequency of patients with values of that compound below the median. Interestingly, another research showed that despite a slightly higher mortality rate, supplementation with vitamin D (25-hydroxyvitamin D) did not affect the hospitalization outcome. Simultaneously, no association was shown between vitamin D levels and the severity of the COVID-19 infection, which is in consent with our results17. Certain studies indicated better outcomes of the vitamin application in older subjects at higher altitudes, with concomitant speculation that those less severe exclusively might respond effectively33. Data presented here shed new light on the actual relation between 25(OH)D and SARS-CoV-2 -related clinical aspects. In addition, it might be possible that reported low vitamin D levels result from the infection-related inflammation and not simply deficiency as suggested in previous reports9. In accordance, some data suggest that measurement of 25(OH)D (reduced in the course of the inflammatory process) cannot be used for evaluation of actual vitamin D status37.
Substantial part of the project was to demonstrate whether 25(OH)D levels are associated with patients’ conditions and viremia. Meta-analyses demonstrated a significant contribution of low vitamin levels to higher severity and mortality, as well as increased risk of SARS-CoV-2 infection33. Quite surprisingly, data from our infected subjects aged between 45 and 70 years showed that vitamin D correlated positively with one of the COVID-19 genes expression ORF1ab. Thus, in the patients already infected with the virus, vitamin D concentrations might not have such an unambiguous beneficial effect on the viremia. Noteworthy, approaches for improving the infected patients’ condition through correcting the vitamin D status should also be carefully considered. Extensive meta-analysis showed that only regular daily vitamin supplementation can positively affect the course of the disease, unlike intermittent bolus dosing as that might induce factors inactivating vitamin D (24-hydroxylase and fibroblasts growth factor 23)22.
The same association was reported in the group of patients with high severity and those hospitalized for more than 2 weeks. That could partially explain other studies’ results where some tendencies were observed for even worse hospitalization outcomes, with higher mortality, in patients additionally supplemented with vitamin D17. In fact, the benefits of vitamin D induction regarding reduced mortality risk were reported exclusively in patients regularly supplemented prior to COVID-19 infection23. Interestingly, only for ORF1ab any significant correlations were demonstrated, with none in N or E viral gene expression. We presume that lack of clearly substantial associations between 25(OH)D and gene-based viremia, and described above clinical parameters, might result from additional contributing factors. Genetic variants resulting in initially lowered 25-hydroxyvitamin D were the ones with no effect of that compound level on the COVID-19 infection outcome. The same study did not support use of vitamin D supplementation in reducing the risk of infection and therapy outcome18. On the other hand, in hospitalized patients with standard intervention due to COVID-19, those with implementation of calcifediol showed a lower risk of admission to intensive care units20. Cumulatively, heterogeneity in the results of vitamin D influence on the infection course and outcome indicates need for further investigation of the role of that compound. Presumably, groups of patients with certain stages of inflammatory processes might benefit from vitamin D supplementation, which additionally seems to support a therapeutic approach rather than directly affecting viral biology.
Previous study suggested that intensified supplementation with vitamin D (5000 IU/d versus 1000 IU/d) might improve recovery time for typical symptoms of SARS-CoV-2 infection – cough and ageusia. Those observation, however, were related to patients from mild to moderate severity, with sub-optimal initial concentrations of that vitamin38. Risk analysis revealed no statistically significant influence of 25(OH)D levels on the occurrence of most common symptoms observed in the course of SARS-CoV-2 infection. Therefore, we cannot link any of the well-known symptoms with levels of 25(OH)D in COVID-19-infected patients. Clinical trials with vitamin D supplementation also support our observations, with no differences between COVID-19-infected subjects treated additionally with the vitamin compared to the placebo group in the context of hospitalization duration, admission to ICU, and ventilation requirement39. Despite no relation between vitamin D and infection-related clinical manifestations, other studies suggested the compound’s crucial role in COVID-19 management. In contrast to our subjects with severe deficiency, data from patients with insufficiency/deficiency compared to those with normal levels of around 50 ng/ml showed that vitamin D negatively correlates with mortality rate40.
Subsequently, we assessed whether the investigated population of patients demonstrated any relation between the vitamin and changes in laboratory data directly associated with subjects monitoring. First, a positive correlation was found between vitamin D and INR levels. Previous studies demonstrated that, in fact, a low (1000 IU) dosage of that compound only affected INR exclusively compared to 5000 IU/d. In addition, they did not show changes in other hemostasis-related parameters, such as platelets (PLT), APTT, and PT38. With further stratification revealed that that relation is present exclusively in subjects with longer hospitalization duration and those with lower expression of the viral genes. No significant correlations were found here between vitamin D and WBC, leukocyte distribution, or PTL, with similar associations demonstrated in the course of systemic bacterial infection—sepsis (also including PCT, CRP, IL-6 in analysis)41. One study demonstrated that higher levels of vitamin D applied (5000 IU) resulted in increased blood concentration of D-dimers, with no changes in those with a daily dose of 1000 IU38. Here, only within patients with high expression of COVID-19 diagnostic genes positive association was found between vitamin D3 and D-Dimer levels. At the same time, that subgroup of patients showed a negative correlation between the studied vitamin and hemoglobin concentration.
Considering the diagnostic laboratory data, we further verified the risk of certain occurrence levels in the context of those parameters. We found inter alia that lower vitamin D was associated with achieving lower WBC values in monitoring, with neutrophils being presumably the most affected population. Interestingly, evaluation of small quantities of vitamin D effect on leukocytes showed a decline in lymphocytes predominantly, followed by monocytes, and no changes in neutrophils38. In contrast, the dose of 25 μg calcifediol daily (equivalent of 3000 to 6000 IU/d) led to an increase in lymphocytes and a reduction in neutrophil level, resulting in reduced neutrophil-to-lymphocyte ratio (NLR). Those effects diminished within a maximum 2 months after discharge from the hospital39. In context of affecting leukocytes, vitamin D levels, and supplementation might be more essential as adjunct therapy. To date, it has been found to influence changes in monocytes and other cells significantly, additionally improving steroid activity42, 43–44. Those effects might be linked with reported improvement of the patients’ status and exacerbation reduction, predominantly in asthmatic patients already managed with standard therapy45. In reference to the correlation with hemoglobin, we also demonstrated that lower vitamin D could result in lower ferritin concentrations in infected patients. Subjects infected with COVID-19 showed previously that supplementation with low vitamin doses is only associated with significant drop in blood ferritin levels38.
Within last several years, the contribution of vitamin D levels to coagulation system function has been shown in various conditions46. Some data suggested that supplementation with calcitriol, in such conditions as cancer, can reduce risk of thromboembolic events47. Relation of vitamin D to hemostasis can be linked inter alia to vitamin D receptor (VDR) presence in megakaryocytes—being the source of the platelets48. Thus, affecting substantial changes in platelet morphology (including mean platelet volume, MPV) that can influence a higher incidence of thrombosis49. Nevertheless, here, we did not find vitamin D levels to contribute to variations in total platelet numbers (PLT) in patients infected with COVID-19. Furthermore, no significant results were obtained when 25(OH)D levels were investigated in the context of their relation to blood saturation, liver function parameters, or coagulation parameters, including INR and D-dimers. It has been recently shown that supplementation with cholecalciferol at high dose (60.000 IU/d for 7 days) can reduce fibrinogen concentration, together with a decline in the frequency of Sars-Cov-2 positive subjects, with no effect on D-dimers29.
This study has several limitations that should be acknowledged. Firstly, the sample size was limited to a single center and a relatively small cohort, which may restrict the generalizability of the findings. Moreover, 25(OH) vitamin D levels were measured only at one time point during hospitalization, which does not allow for assessment of dynamic changes in 25(OH) D status during the course of the illness. Although the expression of the ORF1ab gene was assessed as a marker of active SARS-CoV-2 infection, no viral load quantification was performed, which could have provided additional insights into the relationship between viral activity and immune responses.
Conclusions
Vitamin D, due to its immunomodulatory properties, is a crucial element for the proper functioning of the immune system and the entire body. The COVID-19 pandemic and, therefore, the restrictions resulting from the epidemiological situation have significantly limited access to its natural sources. Despite the presence of severe vitamin D deficiency in patients infected with SARS-CoV-2, no relation with the disease severity was shown. A significant relationship was found between 25(OH)D levels and the duration of hospitalization of SARS-CoV-2-infected patients. Notably, in those with longer hospitalization time and higher viral load, positive correlations of the vitamin with INR and D-dimers were reported, respectively. We did not find any associations between 25(OH)D levels and the prevalence of the clinical symptoms presented by patients at the time of admission. Nevertheless, lower concentrations of 25(OH)D were found to be associated with selected morphological and biochemical parameters, namely leukocyte and neutrophil levels, and ferritin. In accordance with the above, 25(OH)D deficiency reaches severe levels in all hospitalized COVID-19 patients. Even though there is no direct link between its concentration and the infection-related clinical symptoms, the influence on selected hematological parameters might affect the extended therapy duration.
Materials and methods
Patients’ characteristics
Patients with confirmed SARS-CoV-2 infection were enrolled in the cross-sectional study, and a number of 141 subjects were admitted to the Infectious Disease clinics (Department of Infectious Disease and Hepatology and Department of Infectious Disease and Neuroinfections, Bialystok, Podlaskie voivodeship, Northeastern Poland.) between May and December of 2020 (clade 20B and 20C with dominant mutation S: D614G)21. Patients’ plasma was isolated from peripheral blood collected by venipuncture during routine diagnostic procedures. Median number of days between admission to hospital and blood collection was 5 days. Subjects with a mean age of 52 years and equal sex distribution (70 males versus 71 females) were diagnosed with COVID-19 based on positive results of real-time reverse transcription polymerase chain reaction (RT-PCR) analysis. SARS-CoV-2 infection was confirmed prior to hospital admission using RT-PCR performed in a certified diagnostic laboratory. The detection of viral RNA in nasopharyngeal swab, including the expression of the RdRP/ORF1 (spike protein), N (nucleocapsid), and E (envelope protein) was carried out using CE-IVD—marked commercial RT-PCR test kits, following the manufacturers’ protocols. Gene expression of targets was presented as cycle threshold (Ct) values. Ct value is inversely proportional to the amount of viral genetic material present in the sample, with lower Ct values indicating higher viral load and higher Ct values reflecting lower viral load.
Grading of the patients’ condition severity was based on the implemented qualification protocol, including inter alia lung-related symptoms, oxygen saturation, presence of typical COVID-19 symptoms, and chest imaging data (Supplementary Table 1). Informed written consent was obtained from each patient, and the study protocol was approved by the local Ethics Committee of the Medical University of Bialystok (approval number: APK.002.303.2020).
Laboratory data description
Whole peripheral blood, plasma, or serum was used to obtain laboratory data during patients’ routine diagnostics. For the monitoring of the subjects’ condition set of the following parameters was used: white blood cell count (WBC), frequency of lymphocytes (LYMPH), monocytes (MONO), neutrophils (NEUT); hemoglobin concentration (Hb), platelets count (PLT), international normalized ratio of prothrombin time (INR); con-centration of fibrinogen, D-dimers, ferritin; alanine transaminase (ALT) level; oxygen saturation (sO2).
Immunoenzymatic assessment of 25(OH)D
Patient’s plasma samples were used to establish the concentration of the 25-hydroxyvitamin D. Immunoenzymatic assays were performed according to the manufacturer protocols (Human 25-hydroxy vitamin D (25 (OH) D) ELISA Kit; MyBiosource, cat: MBS268910). 25(OH) D concentration-related absorbance was measured at the wavelength of 450 nm using an LEDETECT96 microplate reader (Labexim Products, Lengau, Austria). The standard curve was performed based on the four-parameter logistic (4-PL) curve-fit and subsequently used to estimate the final 25(OH)D concentration. 25(OH)D levels reference range was estimated based on the value: < 30 nmol/L, severe deficiency; 30–50 nmol/L, deficiency; 50–70 nmol/L, insufficiency; > 70 nmol/L, sufficiency22.
Statistical analysis
Biostatistical data analysis was performed using GraphPad Prism 9.0 software (GraphPad Prism Inc.). Shapiro–Wilk, Anderson–Darling and D’Agostiono-Pearson tests were implemented to verify the data distribution before applying specific tests. Unpaired groups were analyzed using the nonparametric Mann–Whitney test. Clinical parameters were correlated with vitamin D levels using the nonparametric Spearman test. Chi-square tests were used to evaluate differences in selected parameter distribution among tested groups and to establish the risk ratio of selected events’ occurrence. The significance level was set at p < 0.05, indicated on the graphs as exact p-value or asterisks: *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.
Author contributions
KG and MM have made a substantial contribution to the project concept. KG, AS, and MM have designed the work and supervised project implementation. KG, AS, DM, APK and AMM have performed the experiments, acquired and analyzed data. KG and AS summarized the data and prepared the manuscript. KG, AS, DM, APK, AMM, SP, RF and MM read and approved the final manuscript.
Funding
This research was funded by Medical Research Agency, Poland; project No. 2020/ABM/COVID19/0001.
Data availability
The data presented in this study are available on request from the corresponding authors.
Declarations
Competing interests
The authors declare no competing interests.
Informed consent
The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethical Committee of Medical University of Bialystok (APK.002.303.2020). Informed consent was obtained from all subjects involved in the study.
Supplementary Information
The online version contains supplementary material available at https://doi.org/10.1038/s41598-025-08621-y.
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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Abstract
SARS-CoV-2 is an RNA virus that caused one of the most significant pandemics in the modern world. Although vaccination and treatment options have advanced, understanding host-related factors influencing disease severity remains critical, especially in the context of emerging variants and long-term complications. Since the beginning, numerous research studies have been conducted to better understand the mechanisms contributing to the severe onset of SARS-CoV-2 infection. Immunomodulatory properties of vitamin D are known for their positive impact on multiple conditions. Nevertheless, clinical trials suggested that vitamin D deficiency did not have as substantial a role as expected in conditions including asthma, cardiovascular or autoimmune diseases, and cancer. Moreover, low vitamin D levels could result from the ongoing inflammatory process. In this cross-sectional study, we assessed the level of 25-hydroxyvitamin D in hospitalized SARS-CoV-2-infected patients using immunoenzymatic tests (ELISA). Furthermore, the expression of the ORF1ab gene was detected, and the obtained results were correlated with laboratory parameters to establish their potential impact on the course of the disease. Severe 25(OH)D deficiency was found in subjects with active SARS-CoV-2 infection. We showed a significant relationship between 25(OH)D and extended hospitalization time. No link was demonstrated between vitamin D levels and clinical manifestations. Lower 25(OH)D values were associated with lower values of leukocytes, neutrophils and ferritin. In summary, our findings highlight the relevance of vitamin D status as a potential modulator of immune response and disease course in SARS-CoV-2 infection, underscoring the importance of continued investigation into host nutritional and inflammatory profiles during COVID-19.
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Neither ProQuest nor its licensors make any representations or warranties with respect to the translations. The translations are automatically generated "AS IS" and "AS AVAILABLE" and are not retained in our systems. PROQUEST AND ITS LICENSORS SPECIFICALLY DISCLAIM ANY AND ALL EXPRESS OR IMPLIED WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES FOR AVAILABILITY, ACCURACY, TIMELINESS, COMPLETENESS, NON-INFRINGMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Your use of the translations is subject to all use restrictions contained in your Electronic Products License Agreement and by using the translation functionality you agree to forgo any and all claims against ProQuest or its licensors for your use of the translation functionality and any output derived there from. Hide full disclaimer
Details
1 Medical University of Bialystok, Department of Regenerative Medicine and Immune Regulation, Bialystok, Poland (GRID:grid.48324.39) (ISNI:0000 0001 2248 2838)
2 Medical University of Bialystok, Department of Infectious Diseases and Hepatology, Bialystok, Poland (GRID:grid.48324.39) (ISNI:0000 0001 2248 2838)
3 Medical University of Bialystok, Department of Infectious Diseases and Neuroinfection, Bialystok, Poland (GRID:grid.48324.39) (ISNI:0000 0001 2248 2838)
4 Medical University of Bialystok, Department of Regenerative Medicine and Immune Regulation, Bialystok, Poland (GRID:grid.48324.39) (ISNI:0000 0001 2248 2838); Medical University of Bialystok, Department of Allergology and Internal Medicine, Bialystok, Poland (GRID:grid.48324.39) (ISNI:0000 0001 2248 2838)