Low Vitamin D Linked to Higher COVID-19 Risk

Vitamin D, a fat-soluble vitamin produced by the skin in response to sunlight, is crucial for strengthening bones, boosting the immune system, and easing inflammation1. Vitamin D deficiency is a global public health issue that arises due to limited sunlight exposure or limited dietary intake. The prevalence of vitamin D deficiency varies among geographic locations but is highest in individuals with dark skin, the elderly, the obese, and those with gastrointestinal illnesses. Low vitamin D levels are linked to numerous health issues, including heart disease, high blood pressure, infections, certain types of cancer, pneumonia, blood clots, and diabetes. Recently, several studies have also associated low vitamin D levels with a higher risk of contracting COVID-19.

In regards to measuring vitamin D deficiency, a value less than 20 ng/mL on the 25-hydroxyvitamin D (25 OH vitamin D) test indicates a vitamin D deficiency, between 20-30 ng/mL indicates a vitamin D insufficiency and anything above indicates sufficient levels of vitamin D.

Research Shows Low Vitamin D Levels Associated with Higher Risk of COVID-19

A University of Chicago Medicine study gathered data from 489 UChicago Medicine subjects who had their vitamin D tested within a year of receiving a COVID-19 test2. Individuals with < 20 ng/mL of circulating vitamin D were twice as likely to test positive for COVID-19 than their vitamin D-sufficient counterparts.

A study of 216 people with COVID-19 at Hospital Marqués de Valdecilla-IDIVAL in Santander, Spain, discovered that 82.2% of the individuals had serum vitamin D levels below 20 ng/mL, a value higher than the prevalence of vitamin D deficiency in the overall population3. The authors of this study reported that the best approach is to identify and treat vitamin D deficiency, especially in high-risk individuals, to maintain 25-OH vitamin D levels above 20 ng/mL and ideally between 30 ng/mL and 50 ng/mL.

Several studies support the use of vitamin D supplements as a COVID-19 preventative measure. One study by Trinity College and the University of Edinburgh found that ambient ultraviolet B (UVB) radiation, important for vitamin D production in the skin, proved to be protective against severe disease and death when used prior to COVID-19 infection4.

“Vitamin D might protect against severe COVID-19 infection”. – Professor Lina Zgaga, Associate Professor in Epidemiology, School of Medicine, Trinity College, and senior researcher on the study.

A group of researchers at the Royal College of Physicians sought to discover the mechanism behind low vitamin D levels and COVID-19 infections5. They found that a principal defense against inflammation and viral infections is T regulatory lymphocytes (Tregs). Low Treg concentrations are reported in people with COVID-19 and can be increased with vitamin D supplementation. Low vitamin D levels are strongly associated with an increased risk of upper respiratory tract infections, obesity, and diabetes, all of which increase an individual’s susceptibility to COVID-19.

A study at the University of Alabama at Birmingham also explored how vitamin D levels might lead to an increased risk of COVID-19 infection6. They found that active forms of vitamin D can inhibit the replication and expansion of COVID-19. Vitamin D, along with lumisterol, can block specific enzymes (RdRP and Mrpo) required for the SARS-CoV-2 life cycle. The study used predicted binding affinities and specific interactions to identify that vitamin D and lumisterol are binding partners of COVID-19 and can act as enzyme inhibitors to prevent further COVID-19 infection. Vitamin D and lumisterol, acting as enzyme inhibitors, present a novel approach to antiviral drug therapy, especially because vitamin D is low-cost and easily accessible.

Vitamin D deficiency has been known to put individuals at a higher risk for viral and bacterial respiratory infections, but its connection to COVID-19 infections and their severity is novel. Several studies have concluded that low levels of vitamin D increase the risk of a COVID-19 infection and that COVID-19 patients have a higher prevalence of vitamin D deficiency than the overall population. Other studies have explored the use of vitamin D supplementation as a preventative measure for COVID-19 infections, which has proved to be effective. Further, some studies have explored the mechanism behind the connection between vitamin D and COVID-19, with conclusions pointing to T regulatory lymphocytes and vitamin D’s enzyme inhibition abilities.

Recently, several studies have associated low vitamin D levels with a higher risk of contracting COVID-19. Existing research on vitamin D shows its promise as a contributing factor in COVID-19 infections and the potential use of supplements as a preventative measure. Further investigation is necessary, however, to determine if it is possible to use vitamin D supplements to prevent COVID-19 infection and to utilize vitamin D as an enzyme inhibitor in antiviral drug therapy.

Interested in Adding Vitamin D to your Lab’s Offering?

Check out our portfolio of active and precursor vitamin D ELISAs, available in individual and bulk quantities.

No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.


  1. WebMD (2021). What to Know About Vitamin D and COVID-19. https://www.webmd.com/lung/vitamin-d-covid-19-what-to-know
  2. UChicago Medicine (2020). Vitamin D deficiency may raise risk of getting COVID-19. https://www.uchicagomedicine.org/forefront/coronavirus-disease-covid-19/vitamin-d-deficiency-may-raise-risk-of-getting-covid19
  3. JCEM (2020). Vitamin D Status in Hospitalized Patients with SARS-CoV-2 Infection. https://academic.oup.com/jcem/article/106/3/e1343/5934827
  4. Trinity College Dublin (2021). Further evidence that vitamin D might protect against severe COVID-19 disease and death. https://www.tcd.ie/news_events/articles/further-evidence-that-vitamin-d-might-protect-against-severe-covid-19-disease-and-death/
  5. Royal College of Physicians (2020). Does vitamin D deficiency increase the severity of COVID-19? https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7385774/
  6. American Journal of Physiology (2021). Vitamin D and lumisterol novel metabolites can inhibit SARS-CoV-2 replication machinery enzymes. https://journals.physiology.org/doi/full/10.1152/ajpendo.00174.2021?utm_campaign=9.9.2021&utm_medium=PressRelease&utm_source=ajpendo

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