Assessment of Serum Vitamin D and Total Calcium Levels in COVID-‎‎19 Infected Patients and Their Relation to Disease Severity

• Vitamin D was proposed as a predictor of COVID-19 severity by many authors. However, the role of hypocalcemia is not well established.
• Serum Vit D level was significantly lower in severe COVID-19 patients (P= 0.04).
• Despite the high prevalence of hypocalcemia in our cohort (88% (86/98), there was no statistically significant difference in serum calcium level between severe and non-severe COVID-19 patients (P= 0.7).
• There was no significant difference between the improved group of patients and the death group as regards the blood levels of both Vit D and calcium.

Previous studies have suggested many risk factors for severe COVID-19 infection. Old age [4] and male sex [5] are principal factors in the suggested clinical severity risk scores. Co-morbidities, such as diabetes mellitus[6], chronic kidney disease, chronic lung diseases, hypertension, and immunosuppression worsen the prognosis and increase the chance of intubation and death [4].

Table (1): Clinical, epidemiological, and laboratory characteristics of the studied population.

Despite the paucity of conclusive evidence that vitamin D supplementation improves COVID-19 disease outcomes, some researchers investigated the relationship between vitamin D status and COVID-19 incidence [17], and disease severity [11, 18], and the number of deaths[10, 19].

The main outcome of this prospective observational study is that low levels of serum vitamin D are related to severe COVID-19 infection in both males and females.

This outcome might be explained by the importance of the active metabolite of vitamin D [1,25(OH)2-D] in the modulation of the growth and differentiation of different immune cell types [20].

The effect of vitamin D deficiency on bacterial and viral infections has previously been studied thoroughly. Some studies showed that people with vitamin D deficiency are more susceptible to acute respiratory tract infections with a higher risk of a prolonged course [19]. Moreover, Vitamin D intake may decrease the rate of pneumonia and bronchitis [21].

Other studies found an association between high seasonal influenza incidence and low vitamin D levels [22]. The risk of tuberculosis was found to be twice as high in patients with low serum levels of vitamin D than in those with normal levels[23].

The main outcome of our study is consistent with the observations of many authors who studied the association between vitamin D status and COVID-19 disease severity and prognosis. A retrospective study carried out in China demonstrated that serum levels of vitamin D were significantly lower in patients with severe COVID-19 than in those with non-severe disease [24]. Moreover, Sulli et al. reported significantly lower serum vitamin D levels in COVID-19 patients compared to controls. They also reported negative correlations between serum levels of vitamin D and D-dimer, CRP, and the severity of CT findings. Moreover, they reported statistically significant positive correlations between serum levels of vitamin D and the partial pressure of oxygen (PaO2), oxygen saturation, and the ratio of PaO2 to fractional inspired oxygen. Finally, they discovered that elderly patients who died during hospitalization had considerably lower vitamin D serum levels than survivors [25].

Panagiotou et al. found that vitamin D deficiency was one of the main risk factors for severe acute respiratory distress syndrome in COVID-19 patients who were admitted to the hospital. They also found that vitamin D deficiency was more common in patients requiring ICU admission than in those who did not. Panagiotou et al. found that vitamin D deficiency was among the leading risk factors for severe acute respiratory distress syndrome in hospitalized COVID-19. They also found that decreased vitamin D was more frequent in patients requiring ICU admission than in those who did not [26].

Another retrospective study carried out in Italy found that COVID-19 patients admitted to the Respiratory Intermediate Care Unit due to respiratory failure had a significant prevalence of vitamin D insufficiency. They also observed a higher risk of death among patients with severe vitamin D deficiency ([27].

Moreover, a prospective study carried out by Radujkovic et al. revealed that COVID-19 patients with vitamin D insufficiency required greater oxygen therapy and invasive mechanical ventilation, resulting in a higher hospitalization rate. They also reported that Vitamin D insufficiency was also linked to a 6-fold increased chance of a severe course of infection and a 15-fold increased risk of fatality [28].

The protective effect of vitamin D in COVID-19  patients could be explained by various mechanisms, one of which involves cathelicidin (LL-37), a bactericidal peptide with antiviral activity. It is produced by macrophages and epithelial cells and induced by vitamin D via intracellular receptors [29]. The main mechanism of the hyper-inflammatory lung damage in severe COVID-19 infection is an increase in angiotensin-2 activity. SARS-CoV-2 interacts with angiotensin-converting enzyme 2 receptors to cause this response, which is aggravated by vitamin D deficiency[30]. Vitamin D also inhibits the release of pro-inflammatory mediators such as interleukin-17 (IL-17) and interferon-gamma by CD4+ T cells and boosts the production of the anti-inflammatory cytokine IL-10. These effects are significantly stronger in females than in males[31].

According to the results of our study, the effect of serum vitamin D levels on COVID-19-related mortality was not significant. This is in line with Luo et al. [24] findings. The limited number of patients that died could clarify this finding.

Although many authors described a distinct link between hypocalcemia and severe illness and mortality [13, 32], the impact of hypocalcemia on COVID-19 is not well recognized. Hypocalcemia is common in critically ill patients. This could be attributed to many factors such as the increase in parathormone secretion, vitamin D deficiency, poor feeding, hypoproteinemia, hypomagnesemia, and drug interactions [33].

The prevalence of hypocalcemia in our cohort was 88% (86/98), and the median serum calcium level was 8.1 mg/dl among patients with severe and non-severe diseases. Based on the definition of hypocalcemia in our study (serum total calcium [34].

The calcium ion is a widely used signaling messenger in all physiological activities of the cell. It is included in all steps of the life cycle of the virus including the formation of virion structure, the passage of the virus into the cell, the expression of a viral gene, the processing of viral proteins, and the maturation and release of the virion[35]. Thus, the high prevalence of hypocalcemia among COVID-19 patients could be explained by the disruption in calcium homeostasis by a high viral load [36].

Many publications have reported the crucial role of hypocalcemia in COVID-19 disease progression and severity. Wu et al. identified hypocalcemia as an independent risk factor for hospitalization [37].Sun et al. found that hypocalcemia (≤2.0 mmol/L) was associated with a higher 28-day mortality rate and a higher incidence of organ injury [38]. Moreover, Osman et al. found an association between hypocalcemia and ICU admission[39].

The current study has some limitations. First, it is a single-center study with small sample size. Second, we considered total calcium levels without considering ionized calcium levels, which may be misleading as in the case of hypoalbuminemia [40]. Third, most patients were elderly (60–80 years) and had co-morbidities, which may have affected disease outcomes. Moreover, leukocytosis was found in some patients; so, the possibility of bacterial co-infection could not be excluded in these patients. Finally, since some patients were lost to follow-up, the associations between vitamin D deficiency, hypocalcemia, and disease outcomes may be imprecise. As a result, we believe that the findings of our study should be further investigated via larger multicenter studies.

CONCLUSION

Our findings support the theory that vitamin D deficiency is a potential risk factor for disease progression and severity in patients with COVID-19. On the other hand, hypocalcemia is not associated with COVID-19 severity despite its high prevalence in these patients.

Ethical Consideration:  The study was done according to the declaration of Helsinki and the sound practices. Informed consent was obtained from all participants in the study. The Ethical Committee of Scientific Research, Faculty of Medicine, Sohag University approved the study procedure with a registration number: Soh-Med-21-06-30.

ClinicalTrials.gov Identifier: NCT 04949412.

Acknowledgments: We would like to thank all health care workers and our patients who help us in the collection of data.

Funding: The authors receive no fund for this research.
Conflict of interest: The authors have no conflict of interest.

Abbreviations: ALT: alanine aminotransferase, AST: aspartate aminotransferase, CBC: complete blood count, COVID-19: Coronavirus disease 2019, CORAD: COVID-19 Reporting and Data System, CRP: C-reactive protein, CT: computed tomography, ICU: Internal Care Unit, IL: interleukin, IQR: interquartile range, PaO2: partial pressure of oxygen, PCR: polymerase chain reaction, SARS-CoV-2: severe acute respiratory syndrome coronavirus 2, SD: standard deviation, SPSS: Statistical Package for the Social Science, Vitamin D: vitamin D, WBCs: white blood cells.