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    by Health By Principle

    A Closer Look at Vitamin D Deficiency and COVID-19


    By Elizabeth Foley

    Recently, there has been increased discussion about vitamin D supplements’ connection to reducing the severity of COVID-19. However, it has been unclear how strong the evidence is to support it. For example, last September, Jennifer Garner asked Dr. Anthony Fauci if vitamin D has “an impact on your susceptibility to infection.” In that interview, Dr. Fauci said, “[I] would not mind recommending—and I take it myself—taking vitamin D supplements.” However, the CDC states that “there is insufficient data to recommend either for or against the use of vitamin D for the prevention or treatment of COVID-19.

    A month later in November, England gave 2.5 million vulnerable individuals free vitamin D pills. The British government made this decision because the pandemic greatly limited those individuals' ability to spend time outside and receive vitamin D from sunlight. Health officials informed the public that vitamin D was particularly important in 2020 because of Coronavirus. However, officials made it clear that there was limited evidence that vitamin D protects against or treats COVID-19.

    Why has there been increased discussion about vitamin D deficiency's relationship to COVID-19? Perhaps because there is an established connection between Vitamin D and the body's respiratory and immune systems. Research shows that vitamin D can strengthen the overall immune system by mounting a stronger and quicker immune response. Science has shown that vitamin D reduces the severity and risk of respiratory infections.

    It is important to consider all the information regarding the relationship between COVID-19 and vitamin D through a scientific lens. Here is a detailed review of the existing research studying the potential link between COVID-19 outcomes and vitamin D deficiency:

    Key Points:

    • Vitamin D can strengthen your immunity and decrease your susceptibility to infection.
    • Research into the connection between COVID-19 and vitamin D deficiency has been small-scale with mixed results.
    • Healthcare officials do not want to cause confusion about vitamin D being a substitute for vaccines.

    A Sparse Number of Large-Scale Studies About Vitamin D and COVID-19

    Considering how much COVID-19 has changed our lives, it can be hard to believe it has been a little more than a year since it set off a pandemic. To that end, there has not been enough time to study the connection between vitamin D and COVID-19 in large-scale studies. On one hand, an ample number of studies point to vitamin D deficiency correlating with significantly worse COVID-19 outcomes. On the other hand, a notable number of studies produced inconclusive results between vitamin D deficiency and severe COVID-19 infection.

    Studies That Suggest Vitamin D Improves COVID-19 Outcomes

    Here are four studies that highlight that the presence of vitamin D in the body can provide improved COVID-19 outcomes. Some of the studies show the benefits of Vitamin D supplementation when experiencing COVID-19, while others found a correlation between a lack of Vitamin D (Vitamin D deficiency) and more severe COVID-19 outcomes.

    The GERIA-COVID Quasi-Experimental Study

    This study took place during 2020 in France. Researchers concluded that vitamin D supplements which were taken regularly during the year prior to a COVID-19 diagnosis contributed to less severe symptoms and a higher survival rate. This study was done with 77 elderly patients who were hospitalized due to COVID-19 infection. The research points to better outcomes for patients who were in the habit of taking vitamin D supplements for a year prior to infection rather than those who began taking vitamin D supplements shortly after diagnosis (1).

    The Journal of Clinical Endocrinology & Metabolism Study of Vitamin D Status in Hospitalized Patients with SARS-CoV-2 Infection

    This Spanish study shows that there is an association between vitamin D deficiency and hospitalization due to COVID-19. Researchers found that out of 200 patients who were hospitalized, over 80 percent were deficient in vitamin D (2).

    The PubMed Association of Vitamin D Levels, Race/Ethnicity, and Clinical Characteristics with COVID-19 Test Results

    This study found an increased risk among Black individuals and severe COVID-19 effects due to vitamin D deficiency. Interestingly, there was no significant association noted for the white individual in this study. Researchers concluded there was a need to examine whether increasing vitamin D levels might decrease the effects of COVID-19 infection (3).

    The JAMA Network Association of Vitamin D Status and Other Clinical Characteristics with COVID-19 Test Results

    This study conducted by the University of Chicago discovered that the risk for testing positive for COVID-19 was 1.77 times greater for patients who had a vitamin D deficiency. Researchers linked individuals who were deficient in vitamin D with a greater likelihood of testing positive for COVID-19. Researchers obtained these results from a sample size of 489 patients. Vitamin D levels were measured in the year before testing positive for COVID-19 in all patients who took part in this study (4).

    Inconclusive Research on the Association between Vitamin D and COVID-19

    Here are two studies that produced inconclusive results about vitamin D deficiency and COVID-19 infection rates:

    The International Journal for Vitamin And Nutrition Research Retrospective Study from a Northern Italian Hospital

    This study was conducted because researchers questioned the findings of several prior studies that suggested vitamin D played a role in reducing the risk of COVID-19. Researchers noted previous studies were based on circumstantial evidence. They observed that studies based on patients' vitamin D levels were still scarce at the time.

    Researchers analyzed a cohort of 375 patients admitted to a northern Italian hospital due to suspected COVID-19 infection. 128 of the patients were found to be positive with COVID-19 infection, while 219 were negative. Vitamin D levels were similar among the group of 375 patients. Since the negative patient group was also low in vitamin D, researchers were unable to conclude any association between vitamin D deficiency and an increased susceptibility to COVID-19 infection (5).

    The Italian Ministry of Health Review Article Questioning if There is a Link between Vitamin D Status, SARS‐CoV‐2 Infection Risk and COVID‐19 Severity

    This review article of the study from the northern Italian hospital patients concluded that poor vitamin D status may be associated with increased risk of infection due to comorbidities. Comorbidities are defined as the presence of one or more disorders in addition to a primary disease or disorder. The reviewers state that vitamin D deficiency in those with comorbidities may play an important role in increasing COVID-19 severity. However, further large-scale research was needed to better understand if comorbidities alone contributed to increased risk of COVID-19 infections, or, if the combination of low vitamin D levels in addition to comorbidities increased patients’ susceptibility to COVID-19 infection (6).

    Research Sample Size

    Since researchers have only become aware of the Coronavirus for a little longer than a year, there has not been adequate time to conduct large-scale studies with sufficient sample sizes. Small-scale studies have demonstrated the benefits of vitamin D for lessening the severity of COVID-19 symptoms, but additional research is needed to fully understand the connection. 

    Research sample size is statistically important because it decreases the margin of error. Large-scale studies with increased sample sizes may further confirm the findings of prior small-scale studies. Ideally, additional large studies will be able to replicate the results of small-scale studies.. However, large-scale studies may also conflict with findings from previous small-scale studies, due to those studies being within the margin of error.

    Vaccine Hesitancy 

    Health officials may be hesitant to promote the use of vitamin D as a defense from COVID-19. Health officials appear to be walking a fine line on this issue in an effort to control the spread of misinformation. According to one study, barriers to taking the COVID-19 vaccine were due to the perspective that “building a robust immune system by using vitamins, specific diets, and other alternative health approaches was seen by some participants as the key to preventing infection” (7).

    This viewpoint may be making healthcare officials reluctant to recommend vitamin D supplements as protection from COVID-19, even if there is convincing evidence to support it, because they do not want to encourage vaccine hesitancy.

    The Bottom Line

    People with inadequate levels of vitamin D are at increased risk of inflammatory diseases and infection. Severe COVID-19 infection is known to be associated with complications due to inflammatory symptoms. Given the evidence from small-scale studies and the established knowledge that vitamin D strengthens our immune response, taking a vitamin D supplement can be potentially beneficial in reducing risk of COVID-19 infection. However, large-scale studies are needed before this can be said with confidence. There is currently no cure for COVID-19. As such, it is important to remember that supplements are no substitute for physical distancing, wearing a mask, or getting a vaccine.








    1. Annweiler, G. (2020). Vitamin D Supplementation Associated to Better Survival in Hospitalized Frail Elderly COVID-19 Patients: The GERIA-COVID Quasi-Experimental Study. MDPI.

    2. Hernández, J. L., Nan, D., Fernandez-Ayala, M., García-Unzueta, M., Hernández-Hernández, M. A., López-Hoyos, M., Muñoz-Cacho, P., Olmos, J. M., Gutiérrez-Cuadra, M., Ruiz-Cubillán, J. J., Crespo, J., & Martínez-Taboada, V. M. (2020, October 27). Vitamin D Status in Hospitalized Patients with SARS-CoV-2 Infection. OUP Academic.

    ‌3. Meltzer, D. O. (2021, March 1). Association of Vitamin D Levels, Race/Ethnicity, and Clinical Characteristics With COVID-19 Test Results. PubMed.

    4‌. Meltzer, D. O. (2020, September 3). Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results. Infectious Diseases | JAMA Network Open | JAMA Network.

    5. Ferrari and Locatelli. (2020, November 2). No significant association between vitamin D and COVID-19. A retrospective study from a northern Italian hospital. International Journal for Vitamin and Nutrition Research.

    6. Ferrari, D. (2021, January 1). Is there a link between vitamin D status, SARSâCoVâ2 infection risk and COVIDâ19 severity? Wiley Online Library.

    7. Momplaisir, Haynes, Nkwihoreze, Nelson, Werner, Jemmott, F. N. H. M. R. J. (2021, February 9). Understanding Drivers of Coronavirus Disease 2019 Vaccine Hesitancy Among Blacks. Clinical Infectious Diseases.