A novel coronavirus disease 2019 (COVID-19) outbreak is a global dramatic pandemic that is immeasurably impacting the communities. Due to lack of data, symptomatic management is used for COVID-19 infection including oxygen therapy and mechanical ventilation for those with severe infection. Considering immunomodulatory, anti-inflammatory anti-fibrotic and anti-oxidant actions of vitamin D, it's safety and ease of administration, as well as direct effects of vitamin D on immune cell proliferation and activity, pulmonary ACE2 expression and reducing surface tension, evaluation of vitamin D supplementation as an adjuvant therapeutic intervention could be of substantial clinical and economic significance. High prevalence of vitamin D deficiency in elderly, smokers, patients with chronic diseases and excess uptake by adipose tissue in obesity make investigations of its role as a secondary therapeutic agent in COVID-19 conceivable. It should be necessary to monitor serum 25(OH)D levels in all inpatient and outpatient populations with COVID-19 to identify the importance of maintaining or promptly increasing circulating levels of 25(OH)D into the optimal range of 100-150 nmol/L.

The aim of this study is to conduct a double blind, randomized, controlled three weeks clinical trial on the efficacy of vitamin D (daily low dose versus weekly high dose) in COVID-19 patients in order to determine the relationship between baseline vitamin D deficiency and clinical characteristics and to asses patients' response to vitamin D supplementation in week three and determine its association with disease progression and recovery.

Subjects who are randomized to high-dose will be asked to take 50,000 IU for two times during the first week and one dose over second and third weeks to quickly raise their serum levels. Subjects in the low-dose arm will take vitamin D 1000 IU daily for three weeks.

In-patients

1. Determine the frequency of low serum Vit D levels (<50 nmol/L) in COVID-19 patients.
2. Determine the relationship between baseline vitamin D status and disease severity, laboratory biochemical tests of white blood cell count (WBC), C-reactive protein (CRP), lymphocyte count, leukocytes counts and neutrophil-lymphocyte-ratio (NLR), lactate dehydrogenase, IL-6, IL-1beta, TNF-alpha platelet count, albumin, and serum ferritin, required hospitalization and intensive care unit (ICU) admission.
3. Asses patients' initial response to vitamin D supplementation in week one and determine its association with disease progression and recovery.
4. Compare disease severity and progression, laboratory biochemical tests of white blood cell count (WBC), C-reactive protein (CRP), lymphocyte count, lactate dehydrogenase, IL-6, IL-1beta, TNF-alpha, platelet count, albumin, and serum ferritin, hospital admission and length of stay, duration of mechanical ventilation, hospital mortality and respiratory failure differ between the early responder and non-responder groups.

Out-patients

1. Determine the frequency of low serum Vit D levels (<50 nmol/L) in COVID-19 patients.
2. Determine the relationship between baseline vitamin D deficiency and clinical characteristics.
3. Asses patients' response to vitamin D supplementation in week three and determine its association with disease progression and recovery

Inclusion Criteria:

Patients with COVID-19:

• ≥ 17 years old
• Both sexes

Exclusion Criteria:

• Patients with dementia, learning disability, mental health needs and alcohol or drug dependency, pregnant women will be excluded.
• Patients with sarcoidosis, hypercalcemia, known vitamin D intolerance