Vitamin D Deficiency Remains an Issue in COVID Infections, Latest Research Shows

young woman coping with loneliness and isolation during CoVid 19 outbreak


Key Takeaways:

  • Vitamin D plays a role in immune support.
  • A new study shows that people who have vitamin D deficiency are 4.6 times more likely to contract COVID-19 compared to people without this deficiency.
  • It’s important to get enough vitamin D daily from a combination of sunshine, food, or supplements.

As the pandemic continues, health-conscious folks are doing everything they can to protect themselves. Researchers continue to investigate why some people fare better after a COVID-19 diagnosis while others do not.

One possibility that has been studied throughout the crisis is the link between COVID-19 and vitamin D deficiency. Building on the work of this previous research, a new study published in the journal Nutrition found that people with a vitamin D deficiency are up to 4.6 times more likely to test positive for the coronavirus.

Vitamin D

Vitamin D is an essential dietary nutrient that’s linked to proper bone health. Beyond bones, low levels of vitamin D can increase the risk of heart disease, type 2 diabetes, tooth decay, and gum disease.

During the pandemic, vitamin D has been making headlines due to its role in immune support and the ability to help fight invading viruses. In fact, there are vitamin D receptors on almost all cells of the immune system, which highlights this vitamin’s important role.

Previous studies have shown that vitamin D deficiency increases susceptibility to viral infections such as hepatitis and influenza. So it makes sense for researchers to see if COVID-19, which is also caused by a virus, is connected to vitamin D status.

Recent studies have shown that COVID-19 patients with acute respiratory tract infections are often deficient in vitamin D.

It’s important to get enough vitamin D, since it improves the physical barrier against viruses and can help make antimicrobial peptides. Vitamin D may also help prevent a cytokine storm, which is a severe and harmful immune over-reaction that’s seen in some COVID-19 patients and can lead to multi-organ failure.

What Did the Latest Study Find?

The 2021 research in Nutrition was a cross-sectional study of a large patient cohort that was part of the i2b2 patient registry platform at the University of Florida Health Center.

The i2b2 registry provides data aggregates from patients who visited several Florida-based health centers, and it allows researchers to search by diagnosis.

The researchers found that patients with vitamin D deficiency were 4.6 times more likely to have a positive COVID-19 status than patients with no deficiency.

This association remained even after controlling for variables such as sex, malabsorption, dental diseases, race, diabetes, and obesity.

It’s important to note that this study is observational in nature, which means that it cannot confirm cause and effect. But it does point out an interesting pattern of disease and risk factors.

In addition to vitamin D deficiency being linked to COVID-19, this research also showed that Black patients were disproportionately affected by COVID-19, dental diseases, and vitamin D deficiency compared with other races.

Dr. Joseph Katz

Seventeen percent of African Americans are vitamin D deficient compared to 5% of the general population.

— Dr. Joseph Katz

Vitamin D and Skin Exposure

Vitamin D is commonly known as “the sunshine vitamin.” That’s because our body is able to make vitamin D when skin is exposed to sunlight.

But in cold climates or when we’re very covered up, we often don’t get enough sunshine to make adequate vitamin D.

Some studies also show that people with darker skin pigments don’t make as much vitamin D from sunshine compared to people with lighter skin pigments.

“Eighty percent of the vitamin D is formed in the skin by sunlight activation," says Dr. Joseph Katz, a professor with the University of Florida College of Dentistry and one of the researchers on the Nutrition study.

“African Americans have more melanin in their skin, which diminishes this process. Seventeen percent of African American are vitamin D deficient compared to five percent of the general population,” he says.

This difference in skin pigmentation may help explain why the study found that black patients were disproportionately affected by COVID-19 and vitamin D deficiency.

Vitamin D from Food

When sunlight is not sufficient, vitamin D can also come from food and supplements. Vitamin D isn’t found in many foods, but it is abundant in fatty fish, eggs, and some fortified beverages, such as milk.

“Seafood such as salmon and trout are some of the best sources of food-based vitamin D,” says Amy Gorin, a plant-based registered dietitian and owner of Plant-Based Eats in Stamford, CT. "In fact, a three-ounce cooked serving of salmon offers more than half the daily value of vitamin D.”

She adds that eggs are a great vegetarian food that offer vitamin D, with 6% of the daily recommendation of vitamin D per egg.

“Since not many foods provide a good amount of vitamin D, fortified foods can be a good option to get your fill of the vitamin from food,” says Gorin.

Look for fortified milk, orange juice, or milk alternatives made from cashews, almonds, oats, or soy.

What About Vitamin D Supplements?

“Vitamin D is considered a nutrient of public health concern, which means that most Americans do not get enough of it, according to the 2020-2025 Dietary Guidelines for Americans,” says Gorin, who explains that more than 90% of people don’t consume enough vitamin D in their diet.

It’s often difficult to get enough vitamin D from foods alone, since few foods are a good source. People often turn to supplements instead.

The only real way to know if you are getting enough vitamin D is to get a blood test. According to the National Institutes of Health, around 18% of Americans have vitamin D blood levels that are too low or inadequate for overall health.

If a blood test isn’t possible right now, consider taking a vitamin D supplement if you:

  • You do not eat foods rich in vitamin D (see list above).
  • You are an older adult.
  • You don’t get a lot of sunshine because you live in a cold climate or keep your skin covered.
  • If you have a dark skin tone.
  • If you have Crohn’s, colitis, celiac, or a similar condition that can hinder vitamin D absorption.

“In many cases, a daily supplement of 1,000 IU (25 mcg) is beneficial, but there are situations—such as severe vitamin D deficiency—where greater amounts are warranted," says Gorin. 

The official upper limit recommended by the Institute of Medicine is set at 4,000 IU (100 mcg)/day.

However, for healthy adults, some research suggests that vitamin D toxicity is unlikely if you stay below 10,000 IU (250 mcg)/day.

“The tricky part is that taking in too much vitamin D via supplements has been linked with negative effects, such as higher risk of bone fractures in the elderly,” says Gorin.

She suggests talking to a trusted healthcare provider before making any supplement changes.

Gorin adds that there are two types of vitamin D—vitamin D2 and vitamin D3. The latter is the recommended type of vitamin D for the biggest health benefit.

What’s Next?

Ultimately, there is still not enough evidence to make firm recommendations about vitamin D supplements for preventing or treating COVID-19.

This will likely change as studies continue to be published and researchers continue to explore the link between vitamin D deficiency and COVID-19.

“The next step in this research should be getting individual data from patients to see whether the increased odds ratio is vitamin D dose-dependent and what the thresholds are,” says Katz. “Then it will be possible to plan prospective studies that will look at the effects of supplements in prevention of COVID-19 and other viral diseases.”


What This Means for You

Vitamin D deficiency is associated with an increased risk of COVID-19. If you don’t get much sunshine or eat fatty fish, consider taking vitamin D supplements to prevent vitamin D deficiency. 

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