Do vitamin D, melatonin, zinc, and vitamin C protect against Covid-19?
Dozens of studies are underway to determine whether supplements of common nutrients and vitamins could help ward off infections of SARS-CoV-2, the coronavirus that causes Covid-19, or even treat the disease by reducing the dangerous inflammation it causes in the lungs and other organs. A few have proven promising. But the research is not yet conclusive on any supplements, and it’s quite inconclusive for others. Meanwhile, scientists caution that too much of any nutrient can have negative side effects.
The greatest benefit of supplements is likely for people who suffer specific nutrient deficiencies.
“Deficiency in one of many essential nutrients can reduce the body’s immune defenses, and fixing these deficiencies with supplements will then be beneficial,” says Walter Willett, MD, a professor of epidemiology and nutrition at the Harvard T.H. Chan School of Public Health. “It doesn’t mean that continuing to increase intake [beyond the body’s needs] will have further benefit.”
Think of a car missing a wheel. Replacing the fourth wheel will make the car work much better, Willett notes, but adding a fifth wheel won’t offer any additional benefit and can actually hamper performance. If you eat well and get enough vitamin D — more on that below — you likely have all the nutrients necessary to build a healthy immune system, and adding extra nutrients doesn’t make you extra healthy.
But the vast majority of Americans don’t meet basic dietary guidelines. “I think it is reasonable for most people to take a multivitamin/multimineral supplement as a nutritional safety net,” Willett tells Elemental, adding that doing so was important for many people before Covid, “and it is more important now.” That holds true for both prevention and if you catch the disease. However, if you have Covid-19, you should discuss any supplements or other treatments with a health care provider. And if you’re taking any medications or have any underlying health issues, it’s important to seek a physician’s advice on preventive supplements, too.
Here are the handful of supplements under the most intense study for effectiveness against the coronavirus:
The logic: Vitamin C is a known antioxidant that bolsters the immune system and, in general, helps prevent inflammation.
General evidence: Vitamin C is thought to help protect against some viral and bacterial infections and lessen symptoms of infections, but evidence on the vitamin’s role even in preventing the common cold is often conflicting. A small study (167 patients) done before Covid-19 existed found that vitamin C infusions during hospital care reduced mortality and cut down on ICU stays for people suffering severe acute respiratory failure and sepsis, which is a dangerous cascade of inflammation throughout the body triggered by an infection. Both of those conditions are leading causes of Covid-19 death.
Covid-19 evidence: Vitamin C might help prevent Covid-19 and also lessen the inflammatory reactions behind some severe Covid-19 cases, according to a review of research on the topic published in the latest issue of the journal Nutrition. But the study authors state clearly that only clinical trials — at least a dozen of which are underway — would prove their suspicions.
“We definitely don’t want to be deficient, but I am not optimistic about any benefit of higher doses,” Willett says.
Dosage: U.S. Recommended Dietary Allowance (RDA) is 75 to 120 milligrams per day (toward the lower for most adults and the higher end for breastfeeding women).
How to get some: Just eat your fruits and veggies and you’ll be fine. One cup of strawberries, red peppers, broccoli, or many other fruits or vegetables gives you all you need.
Risks: While generally considered safe even in high doses, way too much vitamin C — anything above 2,000 milligrams daily—can cause headaches, insomnia, diarrhea, heartburn, and other issues.
“I think it is reasonable for most people to take a multivitamin/multimineral supplement as a nutritional safety net, and it is more important now.”
The logic: Vitamin D is known to help keep bones strong and might bolster the function of immune cells. It’s unusual among vitamins in that it’s rare in foods but is produced by sunlight in the skin and then converted to its usable form in the kidneys. Around 35% to 40% of U.S. adults are thought to have a vitamin D deficiency, and the rate is higher in Black people. However, there is no agreed-upon standard for what constitutes mild, moderate, or severe deficiency.
General evidence: A 2019 review of existing clinical trials indicated vitamin D supplements can reduce the severity of acute respiratory tract infections in hospitalized patients.
Covid-19 evidence: A study early this year 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 treatment should be recommended in Covid-19 patients with low levels of vitamin D circulating in the blood since this approach might have beneficial effects in both the musculoskeletal and the immune system,” said the Spanish study’s co-author, José Hernández, PhD, of the University of Cantabria in Spain. Neither study can say for sure that the deficiency causes the negative outcomes or whether other factors are involved — such as people with the deficiency having other underlying health conditions, or lacking health insurance or access to hospitals.
Yet another study actually tested the effects of vitamin D on Covid-19 patients by adding it to the treatment for one group and not another. Among 26 people who didn’t get the vitamin, half ended up in the intensive care unit and two died. Among the 50 people who got the vitamin, one went to ICU and none died. The results require follow-up research to be conclusive, the scientists wrote in the Journal of Steroid Biochemistry and Molecular Biology. Willett calls vitamin D the “most promising” supplement under study for Covid protection.
Dosage: The U.S. Recommended Dietary Allowance (RDA) for adults is 600 IU (international units) daily. But there’s no firm agreement on this. “I think 2,000 to 4,000 IU per day will get most people out of the deficiency zone and is safe,” Willett says.
How to get some: About 20 minutes of daily sunshine on 40% of exposed skin produces ample vitamin D in general, but such estimates are gross generalities. Dark-skinned people need more exposure to produce the same amount of the vitamin.
Food sources: Salmon (444 IU in three ounces) and other oily fish are excellent sources, as are eggs (44 IU per egg), along with fortified foods including milk and some cereals. If you don’t get out much or don’t have an ideal diet, then: “I think it is reasonable for most people, especially if they have darker skin, to take a [vitamin D] supplement,” Willett says. Note, however, that if you choose a multivitamin, your D-vitamin needs may be covered, so be careful not to let the total exceed 4,000 IU.
Risks: Too much exposure to sun, particularly during midday and especially if it causes sunburns, raises the risk of skin cancer. Excess vitamin D via supplements — anything over 4,000 IU, increases the risk of reversing the beneficial effects, including upping the odds of bone fractures. In rare cases, way too much can be outright toxic.
The logic: Melatonin is a powerful hormone whose production is triggered in the brain by darkness, signaling sleep time. It also supports a healthy immune system directly, and the sleep it promotes is key to a strong immune system. Lack of time outside in bright daylight — a common modern issue — confuses the brain’s biological clock, reducing melatonin production.
General evidence: An overview of immune system benefits from melatonin supplements, published last year in the journal Cell Death & Disease, touted its powerful antioxidant properties and anti-inflammatory effects. In a study of mice in the Journal of Functional Foods, scientists found “the anti-inflammatory and immune-modulatory effects of melatonin may provide a beneficial effect” in treating influenza, which like Covid-19 is primarily a respiratory disease. The role of naturally produced melatonin in sleep is vital, and sleep loss — for just one night and more over time — raises the risk of infections generally, much research finds. Specifically, it reduces the production of proteins and antibodies that fight infections.
Covid-19 evidence: Taking melatonin supplements was linked to a 30% reduction in the likelihood of testing positive for Covid-19 in a November study of data from the Cleveland Clinic, published in the journal PLOS Biology. The reduction was 52% for Black people. Other evidence in the study suggests melatonin might also be effective in treating Covid-19. “I think this data is interesting, but like much other SARS-CoV-2 data, it needs to be further validated with placebo-controlled, randomized controlled studies,” says Melissa Badowski, PharmD, an associate professor of infectious diseases at the University of Illinois at Chicago College of Pharmacy, who was not involved in the study. “We also do not know if these individuals were practicing mask-wearing, hand hygiene, or social distancing. I think there may be a signal, but a lot more research is needed to prove if this signal is valid or not.”
Dosage: There is no federal RDA nor any formal advice on supplement dose ranges. Some countries treat melatonin as a drug rather than a dietary supplement and regulate it accordingly. If you take a supplement, be careful: Too much can cause daytime sleepiness. Ann Pressler, a nurse practitioner at the Cleveland Clinic, says 0.5 to three milligrams should be sufficient. Others advise up to five milligrams.
How to get some: Being outside at least two hours in bright, natural light helps keep the body’s biological clock tuned up and on time, so it makes sufficient melatonin… in the late evening when it’s supposed to make you drowsy.
Risks: Side effects of melatonin supplements include headache, dizziness, nausea, and drowsiness during the day, and in rarer cases anxiety, low blood pressure and other effects — especially in doses above 10 milligrams. It can interact negatively with some medications, including diabetes medicine. Also, the actual ingredients in some supplements, which are unregulated by the federal government, are notoriously unpredictable. A 2017 study found the melatonin content was off by more than 10% compared to what the labels claimed in 71% of 30 supplements analyzed, ranging from 83% less to nearly five times more.
The logic: Zinc helps the body fight bacterial and viral infections. But most people get plenty of zinc in their diets (though vegetarians and people who drink a lot of alcohol may not). Despite being touted as a coronavirus treatment, it’s well behind the pack of other options above.
General evidence: “Oral zinc supplements might benefit people with low levels of zinc,” according to the Mayo Clinic. “Taken soon after cold symptoms appear, zinc might also shorten the length of a cold.”
Covid-19 evidence: Clinical studies are underway to determine if zinc can help treat Covid-19, but for now, “there are insufficient data to recommend either for or against the use of zinc for the treatment of Covid-19,” the National Institutes of Health states.
“This falls in the category of ‘necessary to avoid deficiency, but less promising in higher doses,’” Willett says.
Dosage: Eight milligrams for women, 11 for men. A healthy, varied diet should provide all you need.
How to get some: Oysters and other shellfish, red meat, and poultry are all good options. Other less-effective sources include beans, nuts, seeds, whole grains, and dairy. Cereals are often fortified with zinc.
Risks: Short-term side effects of zinc supplements include indigestion, headache, and vomiting, and zinc can interfere with some drugs, including antibiotics, blood thinners, and some arthritis medications. Over time, too much zinc can cause copper deficiencies, blood diseases, and nerve damage.
The longer list of supplements and alternative remedies promoted for Covid-19 prevention or treatment, without sustaining evidence nor much if any formal research, includes vitamins A and B, herbal teas, essential oils, oleander, tinctures, and colloidal silver.
“There is no scientific evidence that any of these alternative remedies can prevent or cure Covid-19,” states the National Center for Complementary and Integrative Health. “In fact, some of them may not be safe to consume.”
The smartest bet is to take reasonable steps to maintain a healthy immune system by eating well and staying physically active, both of which promote better sleep, adding up to a trio of immunity benefits, says Suzanne Cassel, MD, an immunologist at Cedars-Sinai Medical Center. “You actually don’t want your immune system to be stronger, you want it to be balanced,” Cassel says. “Too much of an immune response is just as bad as too little response.”
If you worry you might have a nutrient deficiency, consult a physician. Otherwise: “Wash your hands, wear a mask, and socially distance,” Badowski advises. “I would recommend this before turning to supplements that we are not sure actually work.”