Experts Clash Over Role of Vitamin D in COVID-19

The evolving list of what makes someone "high risk" for severe COVID-19—darker skin, older age, and obesity, for example—aligns closely with risk factors of vitamin D deficiency, research shows. As a result, some scientists are proposing that vitamin D deficiency may be directly connected to increased risk of severe COVID-19.

"Vitamin D plays an important role in our immune systems," Tiffany Joy Yamut, RN, a registered nurse and co-founder of diet resource site Ketogenic Buddies, tells Verywell. "This may explain why being deficient in vitamin D, which is common in Europeans due to low UV exposure, can increase a person’s likelihood of being infected and hospitalized."

Because vitamin D is known to help prevent respiratory infections, several different studies have explored the potential role it could play in COVID-19.

Vitamin D Deficiency and COVID-19 Risk

In a May study published in Aging Clinical and Experimental Research, researchers from the U.K. looked at data from 20 different European countries, comparing the rates of COVID-19, as well as the death tolls from the disease, with the population’s vitamin D levels.

They reported that countries experiencing higher death rates, like Italy and Spain, also have higher rates of vitamin D deficiency or inadequacy. On the other hand, countries with lower rates of vitamin D deficiency, like Denmark, Sweden, and Norway, have lower rates of COVID-19 infection and mortality.

The researchers also pointed out that vitamin D levels are “severely low” in the aging population, especially in Spain and Italy.

In a smaller study, which was pre-printed in July but has yet to be peer-reviewed, researchers compared prevalence of COVID-19 cases to vitamin D levels in the general population prior to the start of the pandemic. This study, which was pre-printed in July but has yet to be peer-reviewed, analyzed data from 10 countries, including the US, China, Germany, Italy, and Iran. Researchers found a strong correlation between the rates of vitamin D deficiency and severe complications and/or death from COVID-19.

In another pre-printed study, researchers from the University of Chicago Medicine looked at the charts of 499 patients who had their vitamin D levels measured within one year of being tested for COVID-19. They found that patients who had a clinical vitamin D deficiency that was not corrected were almost twice as likely to become infected with COVID-19 than patients who had normal vitamin D levels.

Vitamin D and Your Immune System

Both severe infections and deaths in COVID-19 patients are often linked to an overreaction of the immune system, called a “cytokine storm,” that’s triggered by the virus. When the immune system overreacts, it produces an excessive amount of pro-inflammatory cytokines that can trigger acute respiratory distress syndrome, or ARDS, and widespread tissue damage that can cause organ failure and death.

Targeting cytokines, and trying to prevent or stop this cytokine storm, could be the answer to reducing severity of COVID-19 infections and increasing survival rates, researchers say. Vitamin D could help.

According to a January 2020 report in Nutrients, vitamin D decreases the expression of pro-inflammatory cytokines while simultaneously increasing the expression of anti-inflammatory cytokines. In other words, vitamin D helps reduce the compounds that cause inflammation while producing more of the compounds that decrease inflammation—a combination that could prevent a cytokine storm.

Yamut explains that vitamin D also stimulates the production of cathelicidin, an antimicrobial peptide that helps fight off viruses, bacteria, and fungi. She adds that this could at least partially explain why vitamin D deficiency can lead to viral infections and hospitalization.

Skepticism About Vitamin D and COVID-19

Even though vitamin D is intricately connected to the immune system, some health professionals aren’t convinced that it's the answer to protecting against COVID-19. The results from the above studies drew criticism from a group of doctors from Yale. These doctors say that correlation doesn’t equal causation and, even though vitamin D is vital to immune health, it’s too soon to say whether or not the vitamin is significant when it comes to severity of COVID-19 infection.

Another concern is that the general population will interpret the results incorrectly. Kathleen Suozzi, MD, a Yale Medicine dermatologic surgeon, expressed concern that media coverage of the studies will cause people to take excessive amounts of vitamin D supplements, or even sunbathe too much. While vitamin D toxicity is rare, taking too many supplements can lead to side effects like nausea, vomiting, poor constipation, and weakness. It can also raise the level of calcium in your blood, leading to complications like muscle cramps, irregular heart beat, and even kidney failure.

A review of the studies by the National Institute for Health and Care Excellence (NICE) in the U.K. pointed out that because they are not intervention studies, which measure the effectiveness of a treatment or prevention method, we still don't have any information on how much vitamin D is protective, or whether or not there are adverse effects of taking vitamin D with an active COVID-19 infection.

How Much Vitamin D Do You Need?

Even though vitamin D may not be the panacea for COVID-19, it's still an important part of a healthy diet. In addition to keeping your immune system healthy, vitamin D also plays roles in:

• Calcium balance
• Thyroid health and hormone balance
• Heart health
• Insulin secretion
• Optimal muscle function and bone health

Exactly how much vitamin D you need depends on your health and current vitamin D levels, but the general guidelines from the National Institutes of Health are:

• Babies and infants (up to 12 months): 400 IU (international units)
• Children and adults ages 1 to 70: 600 IU
• Adults over 70 years: 800 IU

How to Get Enough Vitamin D

Sofia Norton, RD, a registered dietitian at Kiss My Keto, tells Verywell that for some people, spending a couple of minutes in the sun can provide all the vitamin D you need for the day. However, this isn't possible for everyone.

"People who have naturally dark skin tone have large amounts of the pigment melanin," she says. "Because of this, their ability to create vitamin D from direct sunlight exposure is reduced."

Because high melanin levels inhibit the production of vitamin D in the skin, this can put certain races at a higher risk of developing vitamin D deficiency. Black adults have the highest prevalence of vitamin D deficiency, followed by Hispanic adults.

Severe COVID-19 infections are disproportionately affecting these racial groups. For example, in New York City, data from April 2020 shows twice as many Black individuals died from the disease as white individuals (92.3 deaths per 100,000 versus 45.2 per 100,000).

Other groups who are at an increased risk for vitamin D deficiency include:

• Older adults
• People with certain health conditions, such as liver diseases, cystic fibrosis and Crohn's disease
• People who are obese
• People who have had gastric bypass surgery

Since not all people can make or absorb vitamin D in the same way, Yamut says her best tip for getting enough vitamin D, regardless of where you live and how old you are, is to make sure that you eat vitamin D-rich foods. Some examples include:

• Salmon
• Trout
• Swordfish
• Mackerel
• Portobello mushrooms
• Halibut
• Atlantic herring
• Sardines
• Whole milk
• Fortified milk

Taking supplements may also help you meet your needs, but always talk to your doctor before adding a new supplement into your diet.

If you decide to take supplements, Yamut recommends going for vitamin D3, also known as cholecalciferol. “This is what your skin produces upon exposure to sunlight,” she says.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.