A century ago before effective antibiotics were available, tuberculosis patients were placed outside on sunny days because sunlight was thought to improve symptoms. Inadvertently, vitamin D, was being used to treat them. The same can be said of the vitamin D-rich cod liver oil used to treat tuberculosis as well. Vitamin D's role in the immune system led scientists to investigate its effects on COVID-19 infection.
A recent study in Internal Emergency Medicine suggests that vitamin D has protective effects against COVID-19 infection and severity. In this large retrospective case-control study using data from Clalit Health Services (CHS), Israel's largest healthcare organization, researchers divided data into two groups to control for confounding factors and to assess the effects of vitamin D levels on COVID-19 risk of infection and on symptom severity once infected.
To examine risk of infection, the first group consisted of more than 41,000 people with PCR-confirmed SARS-CoV-2 infection compared against more than 417,000 control individuals without evidence of infection.
To examine symptom severity once infected, the second group was made up of more than 2500 hospitalized patients with severe symptoms of COVID-19 compared with that same number of patients with PCR-confirmed SARS-CoV-2 infection who did not require hospitalization. All individuals had had their vitamin D levels measured before the pandemic.
Researchers matched for factors of age, gender, geographic region and socioeconomic status and adjusted for factors of BMI, ethnicity and co-morbidities within both groups. Data were from patients before vaccinations were available.
Analyzing these groups for vitamin D levels, researchers found that patients with severe vitamin D deficiency, defined as levels less than 30 nmol/L, were those most likely to contract COVID and have severe symptoms. According to the NIH, blood vitamin D levels between 50 nmol/L and 125 nmol/L are considered adequate.
Vitamin D is thought to be protective against infection by limiting viral replication through antimicrobial peptides and by maintaining cell junctions to limit viral entry. It's thought to protect against some of the more severe symptoms of COVID by protecting against blood clots.
Study limitations the authors noted included a long time range between when vitamin D levels were measured and when infection occurred and a lack of information on treatment with vitamin D supplementation during infection.
Sources: Intern Emerg Med, J Investig Med, NIH
