Published on April 19, 2022

A randomized controlled trial demonstrates effectiveness and safety of vitamin D supplementation against SARS-CoV-2 infection

Key Points

  • A new double-blind, randomized controlled trial found that participants taking vitamin D had a 77% reduced risk of SARS-CoV-2 infection compared to those taking a placebo
  • All participants were highly-exposed frontline healthcare workers who were caring for hospitalized COVID-19 patients, tested negative for a current SARS-CoV-2 infection prior to enrollment, and had not yet been vaccinated
  • There were no safety issues among the participants taking vitamin D


A number of studies, such as those included in the COVID-19 and vitamin D research review eBook and on our COVID-19 and vitamin D review page, have provided much evidence showing the significant effect that vitamin D has on COVID-19 disease progression and outcomes.

Vitamin D is needed for the proper function of immune cells so that they can defend against pathogens and maintain a regulated and effective immune response. In addition, vitamin D supports the function of epithelial cells, and has been shown to regulate the accumulation of certain pro-inflammatory chemicals, thereby reducing the risk of acute respiratory distress syndrome (ARDS), myocarditis, and cardiac injury due to COVID-19. Vitamin D itself has been found to disrupt the function of 19 out of 27 (70%) SARS-CoV-2 proteins, protect the lungs, and regulate the inflammatory response.

Can Vitamin D Supplementation Help Prevent COVID-19?

A new double-blind, randomized controlled trial by Villasis-Keever et al. looked to see how effective vitamin D supplementation was at preventing SARS-CoV-2 infection among highly-exposed frontline healthcare workers who were caring for hospitalized COVID-19 patients. The participants, who tested negative for a current SARS-CoV-2 infection prior to enrollment and had not yet been vaccinated, were randomized to either receive 4000 IU of vitamin D (n=160) or a placebo (n=161) every day for 30 days. PCR testing for SARS-CoV-2 took place at baseline as well as if and when COVID-19 symptoms presented, and testing for SARS-CoV-2 antibodies took place at baseline and at 45 days after enrollment.

What did the study find?

At the end of the study, the participants taking vitamin D had a 77% reduced risk of SARS-CoV-2 infection (based on either a positive PCR test or a positive antibody test) compared to those taking a placebo.

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This finding was independent of the baseline vitamin D status, although an analysis of the data showed that increases in vitamin D level were still predictive of the risk of infection, which adds further support to previous studies linking higher vitamin D levels to lower risk.

The authors also looked at the severity of disease among those who did test positive for SARS-CoV-2, and found no hospitalizations or deaths among the vitamin D group and only one hospitalization among the placebo group. There were no safety issues among the participants taking vitamin D.

Why Vitamin D Level is Important

A review by Grant et al. has defined optimal vitamin D levels necessary to help prevent certain diseases known to be major causes of death, based on a review of the strongest evidence published to date. Diseases identified as those with the highest mortality rates included cardiovascular disease, hypertension, cancer, type 2 diabetes, Alzheimer’s Disease, as well as COVID-19. As the authors state, based on the evidence, “…given the multiple indications of significant health benefits from raising serum 25(OH)D concentrations above 30 or 40 ng/mL as well as the near absence of adverse effects, significant improvements in health at the individual and population levels could be achieved.” These results could be seen simply through achieving and maintaining optimal vitamin D levels!

Everyone responds differently to vitamin D supplementation, due to several key factors. This makes measuring your vitamin D status especially important. Testing and supplementing to reach optimal levels is a safe, simple, and effective way to improve health and help prevent disease – start by finding out your level today!

Make Sure You Are Getting Enough Vitamin D!

Having and maintaining healthy vitamin D levels and other nutrient levels can help improve your health now and for your future. Choose which additional nutrients to measure, such as your omega-3s and essential minerals including magnesium and zinc, by creating your custom home test kit today. Take steps to improve the status of each of these measurements to benefit your overall health. With measurement you can then determine how much is needed and steps to achieve your goals.  You can also track your own intakes, symptoms and results to see what works best for YOU.

Enroll in D*action and Test Your Levels Today!

What Does it Take YOU to Get Your D to 40 ng/ml (100 nmol/L)?

Did you know your health could be greatly affected by making sure you have a vitamin D level of at least 40 ng/ml (100 nmol/L)? Help us help you.

STEP 1 - Do you know what your vitamin D level is? If not, be sure to test today to find out.

STEP 2 – Determine your target level. Are you at your target level? Experts recommend a level of at least 40-60 ng/ml (100-150 nmol/L).

STEP 3 – Need to boost your level? Use the D*calculator to see how much vitamin D it may take to reach your target. Opt for the Loading Dose for a quicker boost.

STEP 4 – Optimize how your body absorbs and utilizes vitamin D with co-nutrients and these simple steps.

STEP 5 – Re-Test! This is an important step to make sure you have reached your target level, and to ensure you are not taking too much! Re-testing after 3-4 months is recommended.

STEP 6 – Adjust, Repeat…

Give your immune system the nutrients it needs to support a healthy you and protect yourself from unnecessary diseases, especially COVID-19.


The first Randomized Controlled Trial on vitamin D and COVID-19 has shown a 96% lower risk of ICU admission for those receiving vitamin D (as 25(OH)D to quickly boost vitamin D blood levels) along with the standard treatment, compared to those receiving standard treatment alone.

These results support many previous observational studies showing a relationship between vitamin D levels and intake and COVID-19 severity.

Review the Latest Nutrient Research for COVID-19

GrassrootsHealth Nutrient Research Institute has launched the new Immune Boost project with the use of our myData-myAnswers nutrient health system that nearly 15,000 people are already using for their health. Specific markers that influence immune health are suggested for testing as part of this project including:

  • Vitamin D
  • Omega-3 Index
  • Essential elements magnesium, selenium, and zinc
  • hsCRP

Our goal is to demonstrate how one can use the Nutrient Research Model established by Dr. Robert Heaney to show the effect of vitamin D serum levels of at least 40 ng/ml (100 nmol/L) on risk reduction for all ethnicities in the population. Status and intake of other nutrients will also be analyzed for any type of relationship to immune status and symptom severity. Join the project today!

Please let us know if you're interested in helping sponsor this project.

CLICK HERE for updates and new information about the project.

Through GrassrootsHealth Nutrient Research Institute, you can also test your essential elements magnesium, copper, zinc and selenium, toxins such as lead, mercury and cadmium, as well as your omega-3 levels, inflammation levels and thyroid stimulating hormone (TSH) level. Find out your levels today! Log on to the test selection page (click the link below) to get your tests and see for yourself if your levels can be improved.

Make sure you track your results before and after, about every 6 months!

Click Here to Access the Test Page

How can I track my nutrient intake and levels over time?

To help you track your supplement use and nutrient levels, GrassrootsHealth has created the Personal Health Nutrient Decision System called

For each specific supplement, you can track what days you take it, how much, and many other details.  This will help you know your true supplemental intake and what patterns of use work for you to reach and maintain optimum nutrient levels. Check it out today!