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Vitamin D and COVID-19: What Doctors Know (and Don't Know) So Far

Research continues into whether supplements can prevent or treat coronavirus infections

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In the early days of the pandemic, when health care workers were struggling to treat patients who poured into emergency rooms sick with COVID-19, a 2017 study landed in David Meltzer's inbox that gave him an idea. It found that people who took vitamin D were less likely to have a viral respiratory tract infection.

"At that point, we had nothing” to treat COVID-19, says Meltzer, M.D., chief of the Section of Hospital Medicine at the University of Chicago. “We didn't have dexamethasone [a steroid now used to help counter inflammation caused by a coronavirus infection] — we truly had nothing. So I thought, Wow, this is worth looking into.”

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In the last year, Meltzer has published two studies exploring vitamin D and its potential impact on COVID-19 risk — and he's not the only one. Several others have investigated vitamin D as a tool for COVID-19 prevention or treatment, and around 50 studies on the subject are currently active or recruiting participants, according to the government's registry of clinical trials.

Why is there such interest in vitamin D?

There are a few reasons researchers have zeroed in on vitamin D, which is perhaps best known for its bone-health benefits. For starters, it plays an important role in immune function and helps keep inflammation in check. And “one of the problems” with COVID-19, Meltzer says, is that some people's immune systems go into overdrive, “and you get inflammation in the lungs and shortness of breath, and all that sort of stuff.”

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Beyond Vitamin D: What About Zinc, Vitamin C, Melatonin and Pepcid?

While vitamin D is the most studied supplement surrounding COVID-19, it isn't the only one. Researchers are also looking into whether vitamin C (an antioxidant with anti-inflammatory properties) and zinc (a mineral also important in immune health) hold any power over the coronavirus. For example, one registered trial will look at the impact intravenous vitamin C has on COVID-19 disease severity; another will study whether combination therapies — zinc, vitamin C, vitamin D and omega-3s — have an effect on COVID-19 complications.

Melatonin and famotidine, an over-the-counter acid reflux medication sold under brand names including Pepcid, are also being studied for COVID-19 treatment. Both were given to former President Donald Trump when he was hospitalized with the disease, along with zinc, vitamin D and other therapies.

But similar to vitamin D, there's not enough research to support their use. In fact, the NIH in its COVID-19 treatment guidelines recommends against taking zinc supplements above the recommended dietary allowance (11 milligrams per day for men and 8 milligrams for women) for the prevention of COVID-19. It also recommends against the use of famotidine for the treatment of COVID-19, except in clinical trials.

Plus, vitamin D deficiency is relatively common, especially among certain populations, including people with dark skin, older adults, individuals who are homebound or in nursing homes, and obese people — all groups that have been hit hard by the coronavirus.

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Another reason for the interest: “In reasonable doses,” vitamin D is safe for most people, explains Robert Shmerling, M.D., senior editor at Harvard Health Publishing and corresponding faculty at Harvard Medical School. Plus it's pretty easy to find. Vitamin D is naturally present in some foods, including salmon and cheese. It can also be obtained through sunlight and supplements.

Where to get vitamin D

  • Sunlight: 5 to 30 minutes of sun exposure at least twice a week
  • Supplements (600 to 800 international units a day)
  • Fatty fish such as trout, salmon, tuna and mackerel
  • Cheese
  • Egg yolks
  • Mushrooms
  • Fortified foods, including cereal, milk and orange juice

Source: NIH

The recommended daily amount of vitamin D is at least 600 international units (IUs) for people ages 19 to 70 and at least 800 IUs for those older than 70, according to the National Institutes of Health (NIH). It's important to keep in mind that too much vitamin D can cause serious health complications. The NIH sets the tolerable upper intake for adults at 4,000 IUs per day.

What does the science say so far about vitamin D?

Several studies have shown an association between low vitamin D levels and increased risk for COVID-19, though not a direct link. A paper published in September 2020 from Meltzer and his colleagues found that people who were vitamin D-deficient were more likely to test positive for COVID-19. A more recent study from Meltzer noted that Black individuals who have higher levels of vitamin D were less likely to test positive for COVID-19 than people with sufficient levels.

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Researchers in Spain reported in August 2020 that a form of vitamin D called calcifediol reduced intensive care admissions among patients with COVID-19. However, a 2020 study conducted in Brazil concluded that a single high dose of vitamin D did not affect disease severity.

Shmerling's advice? “Stand by.” There's not enough scientific evidence right now to prove that vitamin D is helpful in preventing or treating COVID-19, but it's possible we'll get data out of the 50-some ongoing studies “and learn more about who really benefits from extra vitamin D and who doesn't,” he adds.

In the meantime, both experts say there's no downside to taking a supplement or multivitamin that contains the recommended amount of vitamin D — especially if you're concerned you don't get enough through your diet or sunlight. But it's always a good idea to consult a doctor first, especially if you are on other medications.

"There's a lot we don't understand about the biology of this,” Meltzer says. “But in the absence of that, there are some very safe things we can do, like take low-level daily vitamin D supplements and get some sun.”

Meltzer is also a proponent of study participation, and he's currently enrolling adults, including those who have been vaccinated, for two randomized controlled trials to test whether vitamin D supplements can reduce the risk and severity of COVID-19.

What has been proven to prevent and treat COVID?

So far only one drug, remdesivir, has been approved by the Food and Drug Administration (FDA) for the treatment of COVID-19, and several monoclonal antibodies have been authorized under emergency use. Health care providers may also administer other therapies, including antiviral medications, blood thinners and steroids, to help minimize damage from the virus in hospitalized patients.

When it comes to illness prevention, three vaccines — from Moderna, Pfizer-BioNTech and Johnson & Johnson — have cleared FDA authorization. And the Centers for Disease Control and Prevention (CDC) recommends everyday efforts, such as wearing a mask in public and avoiding crowds, to help keep people from getting sick. Experts also stress the importance of a healthy diet for disease prevention, since chronic health conditions associated with poor nutrition and lack of physical activity increase a person's risk for more severe outcomes from a coronavirus infection.

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