Vitamin D and COVID-19: Here's What You Need to Know (Updated January 2021)

The National Institutes of Health (last updated July 17, 2020) states there’s not enough evidence to show that vitamin D can prevent or treat COVID-19. That said, several publications and studies have suggested that maintaining adequate levels of vitamin D would seem potentially beneficial in fighting the COVID-19 infection. Let's dive into the evidence.

We have categorised the studies into prevention and treatment.

Vitamin D Deficiency Increases Your Risk for COVID-19 (Prevention)

Most people in the United States consume less than recommended amounts of vitamin D. An analysis of data from the 2015–2016 National Health and Nutrition Examination Survey (NHANES) found that average daily vitamin D intakes from foods and beverages were 5.1 mcg (204 IU) in men, 4.2 mcg (168 IU) in women, and 4.9 mcg (196 IU) in children aged 2–19 years (NHANES).

To avoid confusion, do take note that there are various studies on vitamin D and COVID-19. Some studies focus on primary prevention meaning whether having sufficient vitamin D in your body will 'prevent' you from getting COVID-19 in the first place. The other type of studies focus on secondary prevention i.e. how vitamin D can prevent those who have already been infected to not succumb to a more severe disease (e.g. cytokine storm, acute respiratory distress (ARDS) or a fatal outcome.

In recent weeks and months, there's been an upshot of studies demonstrating the benefits of vitamin D against COVID-19. More than 100 doctors, scientists and leading authorities have signed an open letter calling for increased use of vitamin D in the fight against COVID-19.

There are many vitamin D studies underway. You can review the status of these trials on clinicaltrials.gov. As of January 2021, 73 studies have been launched to investigate the benefits of vitamin D against COVID-19.

The largest observational study to date, looked at data for 191,779 American patients who were tested for SARS-CoV-2 between March and June 2020 and had their vitamin D tested sometime in the preceding 12 months.

Of those with a vitamin D level below 20 ng/ml (deficiency), 12.5% tested positive for SARS-CoV-2, compared to 8.1% of those who had a vitamin D level between 30 and 34 ng/ml (adequacy) and 5.9% of those who had an optimal vitamin D level of 55 ng/ml or higher.

Data from 14 observational studies — suggest that vitamin D blood levels are negatively correlated with the incidence and/or severity of COVID-19; meaning if your vitamin D level is high, your risk for COVID-19 is low and vice versa.

A study, published in JAMA (JAMA Netw Open. 2020) found that persons who are likely to have deficient vitamin D levels at the time of COVID-19 testing were at substantially higher risk of testing positive for COVID-19 than were persons who were likely to have sufficient levels.

A study of 20 European countries found a link between low levels of vitamin D and higher percentages of COVID-19 cases and mortality. 

Separately, more than 80% of 200 people hospitalized for COVID-19 in Spain were found to be deficient in vitamin D, according to a study published in October in the Journal of Clinical Endocrinology & Metabolism.

Vitamin D and COVID-19 (Treatment)

Two studies in France (C Annweiler, Nov 2020; G Annweiler, Nov 2020), one in India (A Rastogi, Nov 2020) and one in Spain (M Castillo, Oct 2020) showed that Vitamin D supplementation seems to decrease the mortality rate, the severity of the disease, and the inflammatory marker levels among the COVID-19 infected patients, leading to a better outcome and increased survival.

A study published in November 2020 from Singapore (CW Tan, Nutrition 2020), found that those who were started on a daily oral dose of vitamin D3 (1,000 IU), magnesium (150 mg) and vitamin B12 (500 mcg) within the first day of hospitalisation and continued up to 14 days were significantly less likely to require oxygen therapy and further intensive care.

Another publication (Aug 2020) from the International Journal of Infectious Diseases, highlighted that the majority of the Western population is deficient in Vitamin D. According to the author:

• Vitamin D3 supplementation also requires additional vitamin K2 intake.
• The immunoregulating function of vitamin D is promising and might decrease the global epidemic mortality.

Causal loop diagram of the impact of vitamin D3 on the immune system

According to an editorial review (Aliment Pharmacol Ther. 2020) published in June 2020 by Irish researchers, people with vitamin D deficiency appear to be far more prone to severe COVID-19 infections.

Another observational study involving 212 patients in Southeast Asia found that of those with a critical or severe case of COVID-19, only 4% had normal levels, while 96% of those with a mild case of COVID-19 had normal vitamin D levels.

Another study, published in the Irish Medical Journal (May 2020) showed that the calculated COVID-19 mortality rate from 12 European countries shows a significant (P = .046) inverse correlation with the mean 25(OH)D plasma concentration.

The Irish Longitudinal Study on Ageing (TILDA) published in April 2020, suggested that vitamin D deficiency could have serious implications for COVID-19. Results from the Irish Longitudinal Study on Ageing (TILDA), showed that vitamin D plays a critical role in preventing respiratory infections, reducing antibiotic use, and boosting the immune system response to infections.

Another study, published in the journal Nutrients (April 2, 2020), carries the telling title, "Evidence That Vitamin D Supplementation Could Reduce Risk of Influenza and COVID-19 Infections and Death."

A preprinted study published in May 2020, looked at Vitamin D levels and inflammatory markers in hospitalized COVID-19 patients in Germany, South Korea (S. Korea), China (Hubei), Switzerland, Iran, UK, US, France, Spain, Italy (Daneshkhah, MedRxiv 2020). Patients with the lowest Vitamin D levels were about 15% more likely to get severe COVID-19 and cytokine storm. Vitamin D3 plays a role in inhibiting the cytokine storm that causes viral infections to become lethal.

How Much Vitamin D Should You Take?

The vast majority of Americans are vitamin D deficient and could probably benefit from some modest level of vitamin D supplementation.

In the United States, an estimated 41 percent of adults are deficient in vitamin D. People with darker skin are at greater risk — 63 percent of Hispanic people and 82 percent of Black people have low vitamin D levels.

Other factors increase the risk of vitamin D deficiency, including age, limited sun exposure, obesity, and certain medical conditions.

It is difficult to get enough vitamin D from foods, so taking a supplement might be a wise choice but always check with your doctor first.

The RDA (recommended dietary allowances) for vitamin D for men and women more than 50 years of age are 600 - 800 IU (15 mcg - 20 mcg) daily.

The only way to know if you are deficient — and thus need to supplement — is by having your blood levels measured.

Your healthcare provider will measure the storage form of vitamin D, which is known as calcifediol. Anything under 12 ng/ml is considered deficient, and anything above 20 ng/ml is considered adequate.

Although adequacy is measured at 20 ng/ml, many health experts believe that people should aim for blood levels higher than 30 ng/ml for optimal health and disease prevention (Trusted Source).

Additionally, many believe that the recommended intake is far too low and that people need much more to reach optimal blood levels (Trusted Source).

According to the U.S. National Institutes of Health, the safe upper limit is 4,000 IU (100 mcg) per day (nih.gov). Larger doses can be toxic and should only be taken under medical supervision. High levels of vitamin D may cause high calcium level in the blood (hypercalcemia) and calcium salts in kidney (nephrocalcinosis).

Optimize Your Other Nutrients

It's important to keep in mind that nutrients usually don't work in isolation. Many of them depend on one another, and increased intake of one nutrient may increase your need for another.

Some researchers claim that fat-soluble vitamins work together and that it’s crucial to optimize your vitamin A and K intake while supplementing with vitamin D3 (Trusted Source, Trusted Source).

This is especially important for vitamin K2, another fat-soluble vitamin that most people don't get enough of (nih.gov). One can also take 150 to 200 mcg of vitamin K2 per day, as it works synergistically with vitamin D. The only concern is that if you are on Coumadin (anticoagulant), you have to discuss vitamin K2 with your doctor as it will interfere with Coumadin.

Magnesium — another important mineral often lacking in the modern diet — may also be important for vitamin D function (Trusted Source). This is because magnesium helps to activate vitamin D, as the enzymes that metabolize vitamin D in the liver and kidneys require magnesium. In fact, about  half of those taking vitamin D supplements are unable to normalize their vitamin D levels until they take magnesium (BMC Med. 2013).

What Happens if You Take Too Much Vitamin D?

Vitamin D toxicity is extremely rare, but does occur with extreme doses. It is almost impossible to get too much vitamin D from sunlight or food.

According to the U.S. National Institutes of Health, the safe upper limit (tolerable upper intake level) is 4,000 IU (100 mcg) per day. 

Vitamin D toxicity usually develops over time, since extra vitamin D can build up in the body. Nearly all vitamin D overdoses result from taking high amounts of vitamin D supplements.

The main symptoms of toxicity include confusion, lack of concentration, drowsiness, depression, vomiting, abdominal pain, constipation, and high blood pressure (Trusted Source).

Because vitamin D increases calcium absorption in the gastrointestinal tract, vitamin D toxicity results in marked hypercalcemia (high calcium level in the blood) and calcium salts in kidney (nephrocalcinosis).

A recent case report (BMC Geriatrics. 2020): a Brazilian retired 64-year-old female, presented to the emergency service with vomiting, abdominal pain, frontal headache, fatigue, weight loss of 18  kg, severe itchiness, musculoskeletal pain in the limbs and high blood pressure. Due to the rarity of vitamin D toxicity, the definitive diagnosis was prolonged. The diagnosis was confirmed with a Vitamin D blood test. Lab results also showed high level of blood calcium (hypercalcemia) and acute kidney injury.

Wrap-up

Although large randomised controlled trials to prove that vitamin D can combat COVID-19 are needed, current and emerging evidence has demonstrated the promising role of vitamin D.

Of course, the most important thing you can do to avoid infection with coronavirus is to prevent exposure by following the latest recommendations of the CDC and World Health Organization such as wearing face mask, social distancing and hand sanitisation. Also take steps to stay healthy, including getting adequate sleep and exercise and eating a healthful diet that includes adequate (but not excessive) intakes of essential nutrients, such as vitamins C, D and zinc.

For those with hypertension, please take steps to control your blood pressure as high blood pressure (co-morbidity risk factor) is associated with more severe outcome if infected.

Your own immune system, works best when fed right. As long as you are taking supplements under medical supervision and within a safe range, the risk is low but the potential benefit is high. 


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Do take note that you can also get good amounts of vitamins D and C, zinc, and other essential vitamins and minerals from a basic multivitamin.