Can supplements really help fight COVID-19? Here’s what we know and don’t know

Consumers have long turned to vitamins and herbs to try to protect themselves from disease. This pandemic is no different — especially with headlines that scream “This supplement could save you from coronavirus.”

It also helps to have celebrity enthusiasts. When President Donald Trump was diagnosed with COVID-19, his pill arsenal included Vitamin D and zinc. And in an Instagram chat with actress Jennifer Garner in September, infectious diseases expert Anthony Fauci touted vitamins C and D as ways that might generally boost the immune system. “If you’re deficient in vitamin D,” he noted, “that does have an impact on your susceptibility to infection. I would not mind recommending, and I do it myself, taking vitamin D supplements.”

But whether over-the-counter supplements can actually prevent, or even treat, COVID-19, is not clear. Since the disease is so new, researchers haven’t had much time for the kind of large experiments that provide the best answers. Instead, scientists have mostly relied on fresh takes on old data. Some studies have looked at outcomes of patients who routinely take certain supplements — and found some promising hints. But so far there’s little data from the kinds of scientifically rigorous experiments that give doctors confidence when recommending supplements.

Here’s what we know today about three supplements getting plenty of attention around COVID-19.

Vitamin D

What it is: Called “the sunshine vitamin” because the body makes it naturally in the presence of ultraviolet light, Vitamin D is one of the most heavily studied supplements (SN: 1/27/19). Certain foods, including fish and fortified milk products, are also high in the vitamin. 

Why it might help: Vitamin D is a hormone building block that helps strengthen the immune system.

How it works for other infections: In 2017, the British Medical Journal published a meta-analysis that suggested a daily vitamin D supplement might help prevent respiratory infections, particularly in people who are deficient in the vitamin.

But one key word here is deficient. That risk is highest during dark winters at high latitudes and among people with more color in their skin (melanin, a pigment that’s higher in darker skin, inhibits the production of vitamin D).

“If you have enough vitamin D in your body, the evidence doesn’t stack up to say that giving you more will make a real difference,” says Susan Lanham-New, head of the nutritional sciences department at the University of Surrey in England.

And taking too much can create new health problems, stressing certain internal organs and leading to a dangerously high calcium buildup in the blood. The recommended daily allowance for adults is 600 to 800 international units per day, and the upper limit is considered to be 4,000 IU per day.

What we know about Vitamin D and COVID-19: Few studies have looked directly at whether vitamin D makes a difference in COVID-19.

In May, in the BMJ Nutrition, Prevention & Health, Lanham-New and her colleagues published a summary of existing evidence and concluded that there’s only enough to recommend vitamin D to help with COVID-19 prevention for people who are deficient. That paper made inferences from how vitamin D works against other respiratory tract infections and immune health.

More than a dozen studies are now testing vitamin D directly for prevention and treatment, including a large one led by JoAnn Manson, a leading expert on vitamin D and an epidemiologist and preventive medicine physician at Harvard Medical School and Brigham & Women’s Hospital in Boston. That study will analyze if vitamin D can affect the course of a COVID-19 infection. The trial aims to recruit 2,700 people across the United States with newly diagnosed infections, along with their close household contacts.

The goal is to determine whether newly diagnosed people given high doses of vitamin D — 3,200 IU per day — are less likely than people who get a placebo to experience severe symptoms and need hospitalization. “The biological plausibility for a benefit in COVID is compelling,” she says, given the nutrient’s theoretical ability to impede the severe inflammatory reaction that can follow coronavirus infection. “However the evidence is not conclusive at this time.”

Zinc

What it is: Zinc, a mineral found in cells all over the body, is found naturally in certain meats, beans and oysters.

Why it might help: It plays several supportive roles in the immune system, which is why zinc lozenges are always hot sellers in cold and flu season. Zinc also helps with cell division and growth.

How it works for other infections:  Studies of using zinc for colds — which are frequently caused by coronaviruses — suggest that using a supplement right after symptoms start might make them go away quicker. That said, a clinical trial from researchers in Finland and the United Kingdom, published in January in BMJ Open did not find any value for zinc lozenges for the treatment of colds. Some researchers have theorized that inconsistences in data for colds may be explained by varying amounts of zinc released in different lozenges.

What we know about zinc and COVID-19: The mineral is promising enough that it was added to some early studies of hydroxychloroquine, a drug tested early in the pandemic. (Studies have since shown that hydroxychloroquine can’t prevent or treat COVID-19 (SN: 8/2/20).)

In July, researchers from Aachen University in Germany wrote in Frontiers in Immunology that current evidence “strongly suggests great benefits of zinc supplementation” based on looking at similar infections including SARS, another disease caused by a coronavirus. For example, studies suggest that giving zinc reduces the risk for death from a pneumonia infection. The researchers cite evidence that zinc might help prevent the virus from entering the body, and help slow the virus’s replication when it does.

Another review — also based on indirect evidence — published August 1 in Advances in Integrative Medicine also concluded that zinc might be helpful in people who are deficient.

In September, researchers from Hospital Del Mar in Barcelona reported that among 249 patients studied, those who survived COVID had higher zinc levels in their plasma (an average of 63.1 mcg/dl) than those who died (43mcg/dl).

Overall, though, the jury is still out, says Suma Thomas, a cardiologist at the Cleveland Clinic Foundation, who in June led a team that reviewed the evidence for popular supplements in the Cleveland Clinic Journal of Medicine. Given what’s already known, zinc could possibly decrease the duration of infection but not the severity of symptoms, she said, particularly among people who are deficient. About a dozen studies are now looking at zinc for COVID-19 treatment, often with other drugs or supplements.

Thomas and her colleagues are comparing symptom severity and future hospitalization in COVID-19 patients who take zinc with and without high doses of vitamin C with those who receive ordinary care without the supplement. Results are expected soon, she says.

Vitamin C

What it is: Also called L-ascorbic acid, vitamin C has a long list of roles in the body. It’s found naturally in fruits and vegetables, especially citrus, peppers and tomatoes.

Why it might help: It’s a potent antioxidant that’s important for a healthy immune system and preventing inflammation.

How it works for other infections: Thomas cautions that the data on vitamin C are often contradictory. One review from Chinese researchers, published in February in the Journal of Medical Virology, looked at what is already known about vitamin C and other supplements that might have a role in COVID-19 treatment. Among other encouraging signs, human studies find a lower incidence of pneumonia among people taking vitamin C, “suggesting that vitamin C might prevent the susceptibility to lower respiratory tract infections under certain conditions.”

But for preventing colds, a 2013 Cochrane review of 29 studies didn’t support the idea that vitamin C supplements could help in the general population. However, the authors wrote, given that vitamin C is cheap and safe, “it may be worthwhile for common cold patients to test on an individual basis whether therapeutic vitamin C is beneficial.”

What we know about Vitamin C and COVID-19: About a dozen studies are under way or planned to examine whether vitamin C added to coronavirus treatment helps with symptoms or survival, including Thomas’ study at the Cleveland Clinic.

In a review published online in July in Nutrition, researchers from KU Leuven in Belgium concluded that the vitamin may help prevent infection and tamp down the dangerous inflammatory reaction that can cause severe symptoms, based on what is known about how the nutrient works in the body.

Melissa Badowski, a pharmacist who specializes in viral infections at the University of Illinois at Chicago College of Pharmacy, and colleague Sarah Michienzi published an extensive look at all supplements that might be useful in the coronavirus epidemic. There’s still not enough evidence to know whether they are helpful, the pair concluded in June in Drugs in Context. “It’s not really clear if it’s going to benefit patients,” Badowski says.

And while supplements are generally safe, she adds that nothing is risk free. The best way to avoid infection, she says, is still to follow the advice of epidemiologists and public health experts: “Wash your hands, wear a mask, stay six feet apart.”