In this cross-sectional study, 556 patients were studied, 13% of them were admitted to the ICU ward. About half of them were men. Most of them were overweight or obese and one-third had minimally one comorbidity. In 44% of cases, the disease was severe or critical and the hospital mortality rate was 10.8%. Two-third of patients had vitamin D deficiency. There was a negative correlation between disease severity and history of vitamin D supplementation, serum levels of 25 OH Vitamin D, calcium, phosphorus, and albumin. Also, there was a negative correlation between in-hospital mortality and serum levels of 25 OH vitamin D and calcium.
Age was both a risk factor for COVID-19 disease and its severity in this study. Patients with severe illness or those who died were 15 years older than those with mild illness or who have complete recovery (median age 49 vs. 65 years). The mortality rate in patients over 60 years of age is more than five times that of people <=30 years. This finding is consistent with the findings of previous studies.20 In these studies, the median age of patients with severe disease was 9-17 years higher than median age in people with the mild disease. 21-23 They have also reported that the age of 65 or older increases the risk of death by 3.7 to 6 times. 24, 25 For every 5 years of increase in patient age in the USA, the chances of hospitalization and mortality in the hospital increase by 34% and 10-18%, respectively. 26,27 Numerous factors are involved in increasing the severity of the disease and mortality with age. The imbalance of the immune system and comorbidities intensifies the severity of the disease and consequently increases the mortality rate due to pathogens such as COVID-19 in elderly.28
In this study, there was no significant difference between gender and disease severity and outcome. In a review article, the male-to-female ratio in patients admitted for COVID-19 was similar in three studies in France, Spain, and Switzerland. 29 But, mortality among men was 1.7-1.8 times higher than women, and this ratio was higher in those under 60 years of age. Male sex hormones, concurrent diseases, behavioral differences, and more exposure of men to pathogens may play a role in this differences. Although, women have less access to medical services in some countries and the proportion of women with COVID-19 disease and their mortality may be underestimated.
There was no relationship between comorbidities such as diabetes mellitus and hypertension and ischemic heart disease with the severity of COVID-19 disease and its outcome in this study. In different studies, the prevalence of hypertension, diabetes, cardiovascular disease and obesity varied from 9-56%, 7-34%, 2-33% 30, 31 and 13-69% 32, 33, respectively. Contrary to our study, in some studies, these factors have been associated with increased severity of COVID-19 disease and associated mortality. This discrepancy may be due to different method of study and participant characteristics. In this study, the diagnosis of comorbidities was based on medical history and drug taking history. We didn't online access to the patient's previous medical record. Differences in demographic characteristics such as age are also an important factor that explains the discrepancy in the studies results. In those studies, the average age of participants was at least a decade higher and the male prevalence was 10 percent higher than in our study. However, after adjusting for confounding factors such as age, sex, and co-morbidities, only the age relationship remained significant in some of these studies. 34-37
In the present study frothy percent of patients had 25 OH Vitamin D less than 20 ng/ml. Vitamin D deficiency was more common in women than men. Contrary to expectations, although Iran is a sunny country, vitamin D deficiency is common in all age groups. The reason is the lack of intake through food, reduced synthesis of this vitamin in the skin, and the type of clothing. 38-39
There was a negative correlation between disease severity and serum levels of 25 OH vitamin D in this study. The mean level of 25 OH Vitamin D in patients admitted to the intensive care unit was 11 ng / ml less than other groups, and also vitamin D deficiency was more common among them. This finding has been shown in other studies. In a cohort study by Baktash et al 40 on people with COVID-19 older than 65 years, the median level of 25 OH vitamin D was lower than that of healthy controls. The difference in 25 OH vitamin D between the two groups in their study was much greater than our study (62 vs. 11 ng / ml). Of course, they have compared patients with healthy people, but we have compared patients with different degrees of illness. The age of the study participants was at least 65 years, which is much higher than the average age of the participants in our study (81 vs. 53 years). But Hastie 41 and Panagiotou do not confirm these findings. In the Hastie study, vitamin D deficiency was associated with more severe disease, but after adjusting for confounding factors, this effect disappeared. In a study of vitamin D levels in COVID-19 patients, Panagiotou et al found that mean vitamin D levels were not associated with disease severity, but that vitamin D deficiency was more common in patients admitted to the intensive care unit. They treated patients with vitamin D supplements immediately after the diagnosis of vitamin D deficiency, which may have affected the course of the disease. 42
Vitamin D supplementation (those who received at least 50,000 units of vitamin D in the past month) was associated with reduced disease severity and mortality in this study. There are articles point to the role of vitamin D in reducing the risk of COVID-19 disease and morbidity and mortality of this disease 43.
There are evidences to suggest a link between vitamin D levels and COVID-19 disease, some of which we have already mentioned and will address in more detail here. In severe COVID-19 disease, the balance of the immune system is upset. The immune system does not have the proper response to prevent the multiplying and progressing virus infection. Instead, cytokine storms occur due to the release of excessive inflammatory factors. In several other observational and ecological studies, such as ours, vitamin D deficiency has been more common in patients with COVID-19. The multiple effects of vitamin D in reducing the incidence, severity and mortality of Covid-19 disease can be explained by several different mechanisms. First, vitamin D has antibacterial and antiviral property by regulating innate and adaptive cellular immunity, and physical barriers. Vitamin D produces antimicrobial peptides (AMPs) such as s cathelicidins and defensins by activating immune cells. Cathelicidins inactivate viruses such as influenza A virus by destroying envelope proteins. A primary form of cathelicidins is known as LL-37, which prevents the virus from entering the cell. Second, one of the characteristic of severe COVID-19 disease is the presence of a "cytokine storm." In this condition, inflammatory cytokines such as IL-6, IL-8, CRP and ferritin are released without the control of the immune system. Inflammatory cytokines damage the integrity of the lungs by causing inflammation, leading to pneumonia, which in turn causes a vicious cycle. IL-6 increases the severity of COVID-19 by rearranging the angiotensin-converting enzyme (ACE2) receptors and inducing macrophage cathepsin L. Cathepsin L of macrophage cleaves the S1 subunit of the corona virus spike glycoprotein. This is essential for the coronavirus to enter human host cells, fusion of endosome membrane of virus–host cell, and release of viral RNA. Vitamin D can modulate the immune system and reduce the production of pro-inflammatory markers. Vitamin D supplementation has reduced interleukin-6 levels in several clinical trials. Third, Vitamin D may reduce the risk of ARDS and mortality from COVID-19 by raising ACE2 levels. COVID-19 infection the SARS-COV-2 virus binds to the ACE2 receptor expressed on the surface of lung epithelial cells and causes over-accumulation of angiotensin II by ACE2 downregulation. In the in-vivo studies, vitamin D-binding protein has played a role in this interaction. Calcitriol, the active metabolite of vitamin D, increases ACE2 expression in the lungs in animal studies. Vitamin D replacement may reduce lung damage by increasing ACE2 expression and synthesis of α-1-antitrypsin by CD4 + T cells. α-1-Antitrypsin is critical for lung integrity and repair, and is required for further production of anti-inflammatory interleukins such as IL-10. Fourth, vitamin D improves endothelial dysfunction by reducing the oxidative stress of free oxygen radicals,TNF-alpha and interleukin-6 and suppressing the NF-κB pathway. Endothelial dysfunction causes vascular inflammation and increased blood coagulation, which is seen in severe COVID-19. Fifth, Vitamin D reduces the lung damage caused by COVID-19 by stimulating the proliferation and migration of alveolar epithelial cells type II and reducing their apoptosis. It also inhibits mesenchymal transition of epithelial cell which induced by TGF-β. In COVID-19, the function of type II pneumocytes is impaired, and the surfactant concentration decreases at the alveolar surface, and the alveoli are collapsed. In some studies, 1α, 25 (OH) 2D have caused an increase in surfactant and may be prevent from lung alveoli collapse. Sixth, Age, virus mutations, and race of patients may have influenced studies and altered results. Studies have shown that acute inflammatory disease can decrease serum levels of 25 hydroxyvitamin D. These changes were temporary and short-lived and resolved within 24-48 hours. Therefore, the timing of blood sampling from patients from the onset of symptoms and disease can change the results. And these complicate the interpretation of the results.44-52
In the present study, the prevalence of hypocalcemia, hypophosphatemia, and hypoalbuminemia was high, and patients with more severe disease had lower blood levels of calcium, phosphorus, and albumin. Also, hypocalcemia and hypoalbuminemia were directly related to poor outcome and mortality. Similar results have been found in other published articles. In one study, among patients with COVID-19, serum calcium levels were 0.8 mg/dl lower than in other patients and mean serum calcium levels can predict the prognosis with 73% accuracy.53, 54 Patients who died of COVID-19 had a serum albumin level of 4.6 g / L lower than those who survived 55 and hypoalbuminemia was an independent predictor of mortality and increased the risk 6.3-fold (OR=6.39; 95% CI=1.31‐31.09). 56 This relationship can be explained in several aspects. First, each of these substances (vitamin D, calcium, and albumin) have a special role in the function of the immune system and various parts of the body and through it exerts its effect. Second,The deficiency of these substances is an indirect index of the patient's nutritional status or concomitant conditions such as obesity, kidney failure, liver failure, and diabetes which are associated with vitamin D deficiency.
In this study, 44% of patients needed advanced respiratory care and 13% needed to be admitted to the ICU. The in-hospital mortality rate was 10.8%. In this study, the number of patients who admitted to ICU is 3.8 times and in- hospital mortality rate is twice the globally national death rate in Iran. According to the World Health Organization and the Ministry of Health of Iran, as of November 24, 2020, about 841,308 people have been infected with COVID-19, and 603,445 have recovered. 44,327 (5.2%) people have died and 5,796 (2.81%) are in critical condition and admitted to ICU.57,58 This study was performed at the time of the first peak of the disease in Iran. At that time, the number of PCR tests performed to diagnose COVID-19 was low, and only symptomatic individuals referred to hospitals were tested. Our hospital is a tertiary and referral center for respiratory diseases and COVID-19. Therefore, more serious patients refer to this center and one-fifth of our patients had over 70 years old. Of course, in-hospital mortality in this study is lower than in other centers. About 32-40% of hospitalized patients need to be admitted to the ICU and their mortality rate is about 15-39% in other studies. 59,60 Experienced and well-trained personnel to care for patients with respiratory disorders and infectious disease and access to adequate facilities for non-invasive and invasive ventilation can justify these results.