High-Dose Vitamin C and Zinc Supplements Ineffective for COVID-19 Treatment, Trial Shows

Prevention strategies, including social distancing, wearing face coverings and taking one of the three COVID-19 vaccines authorized by the Food and Drug Administration (FDA) are effective for reducing the spread of COVID-19. So far, the FDA has approved only one medication for treating COVID-19 infection, remdesivir (VEKLURY), which is used only in patients hospitalized with the disease.

Unfounded claims about the supportive roles of vitamin C and zinc for treating COVID-19 infection have led to increased demand and expenditures for these supplements, among others.[1]

Evidence from a recent study that was conducted by Cleveland Clinic researchers refutes these claims.[2] The study was published online in the Journal of the American Medical Association (JAMA) Network Open on February 12, 2021.

About vitamin C and zinc

Vitamin C is an essential water-soluble nutrient.[3] It acts as an antioxidant (helps to protect cells from damage). It also plays a role in wound healing and improving the absorption of iron from plant-based foods and helps the immune system to work properly to protect the body from disease. The recommended daily intake of this vitamin is 90 milligrams (mg) for adult men and 75 mg for nonpregnant adult women. Good dietary sources of vitamin C include citrus fruits (such as grapefruit and oranges), kiwifruit, green and red peppers, and other fruits (such as strawberries) and vegetables (such as potatoes, broccoli and tomatoes).

Zinc is an essential mineral that is needed by all cells in the body to make proteins and carry out other critical functions.[4] It also helps the body’s immune system combat bacterial and viral infections, promotes wound healing and is needed for normal childhood growth and development. The recommended daily intake for zinc is 11 mg for adult men and 8 mg for nonpregnant adult women. Zinc is naturally present in high amounts in certain foods, such as oysters, red meat and poultry. It also is available in smaller amounts in beans, nuts and other foods.

Most people get enough vitamin C and zinc from their diet. However, people who smoke or are exposed to secondhand smoking and those who do not eat a good variety of foods may not be getting enough vitamin C from their diet.[5] Similarly, individuals with chronic illnesses (such as those with chronic kidney or liver disease) and those with digestive disorders (such as ulcerative colitis) may not absorb enough zinc from their diet.[6] Such people may need to take a dietary supplement that contains these nutrients, as applicable.

The new study[7]

The JAMA Network Open study was a randomized clinical trial that was conducted in outpatient hospital clinics in Florida and Ohio from April 27 to October 14, 2020. It was designed to enroll 520 adult subjects who tested positive for COVID-19 and were likely to remain in the outpatient setting during their treatment. The subjects were randomized to receive either 8,000 mg of vitamin C, 50 mg of zinc gluconate (zinc), both or neither of these supplements for 10 days. The trial’s primary endpoint was the number of days required to reach a 50% reduction in COVID-19 symptoms, including severity of cough, fever, fatigue and shortness of breath.

The trial was stopped early because there was evidence after enrolling only 214 subjects that the supplements were not beneficial. Subjects who did not receive either supplement achieved a 50% reduction in their COVID-19 symptoms after 6.7 days on average compared with 5.5 days for those in the vitamin C group, 5.9 days for those in the zinc group and 5.5 days for those who took both supplements.

The trial also showed that gastrointestinal adverse effects (diarrhea, nausea, or stomach pain or cramps) were reported by 7% to 16% of the subjects who took one or both supplements but were not reported by any of those who did not take either supplement.

Importantly, previous studies showed that zinc toxicity from supplements can cause copper deficiency, resulting in neurological problems, including numbness and weakness in the arms and legs.[8],[9]

Furthermore, vitamin C and zinc supplements can interact with some medications. For example, vitamin C supplements can interact with certain cholesterol-lowering medications,[10] and zinc supplements can interact with certain antibiotics.[11]

Therefore, the trial researchers concluded that these supplements should not be recommended to reduce symptoms in COVID-19 patients treated in outpatient settings. Notably, this conclusion aligns with the recommendations of the National Institutes of Health’s COVID-19 Treatment Guidelines Panel. As of press time, the panel does not recommend taking or not taking vitamin C or zinc supplements for the treatment of COVID-19 in noncritically ill patients[12],[13] and explicitly recommends against the use of high-dose zinc supplements for the prevention of COVID-19 outside of clinical trials.

What You Can Do

Do not resort to vitamin C or zinc supplements to treat or prevent COVID-19. It is best to rely on dietary sources for your recommended daily intake of these and other essential nutrients. Talk to your doctor before you start taking any supplements.
 

References

[1] Fortune Business Insights. Immune health supplements market size 2021: Is projected to reach USD 31.50 billion by 2028, exhibiting a CAGR of 6.6%. May 5, 2021. https://www.globenewswire.com/en/news-release/2021/05/05/2223219/0/en/Immune-Health-Supplements-Market-Size-2021-Is-Projected-to-Reach-USD-31-50-Billion-by-2028-Exhibiting-a-CAGR-of-6-6.html. Accessed June 13, 2021.

[2] Thomas S, Patel D, Bittel B, et al. Effect of high-dose zinc and ascorbic acid supplementation vs usual care on symptom length and reduction among ambulatory patients with SARS-CoV-2 infection: The COVID A to Z Randomized Clinical Trial. JAMA Netw Open. 2021;4(2):e210369.

[3] National Institutes of Health, Office of Dietary Supplements. Vitamin C fact sheet for consumers. March 22, 2021. https://ods.od.nih.gov/pdf/factsheets/VitaminC-Consumer.pdf. Accessed June 13, 2021.

[4] National Institutes of Health, Office of Dietary Supplements. Zinc: Fact sheet for health professionals. March 26, 2021. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional. Accessed June 13, 2021.

[5] National Institutes of Health, Office of Dietary Supplements. Vitamin C fact sheet for consumers. March 22, 2021. https://ods.od.nih.gov/pdf/factsheets/VitaminC-Consumer.pdf. Accessed June 13, 2021.

[6] National Institutes of Health, Office of Dietary Supplements. Vitamin C fact sheet for health care professionals. March 26, 2021. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional/. Accessed June 13, 2021.

[7] Thomas S, Patel D, Bittel B, et al. Effect of high-dose zinc and ascorbic acid supplementation vs usual care on symptom length and reduction among ambulatory patients with SARS-CoV-2 infection: The COVID A to Z Randomized Clinical Trial. JAMA Netw Open. 2021;4(2):e210369.

[8] National Institutes of Health, Office of Dietary Supplements. Zinc: Fact sheet for health professionals. March 26, 2021. https://ods.od.nih.gov/factsheets/Zinc-HealthProfessional. Accessed June 13, 2021.

[9] National Institutes of Health, Office of Dietary Supplements. Zinc fact sheet for consumers. December 10, 2019. https://ods.od.nih.gov/pdf/factsheets/Zinc-Consumer.pdf. Accessed June 13, 2021.

[10] National Institutes of Health, Office of Dietary Supplements. Vitamin C fact sheet for health care professionals. March 26, 2021. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/. Accessed June 13, 2021.

[11] National Institutes of Health, Office of Dietary Supplements. Vitamin C fact sheet for health care professionals. March 26, 2021. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/. Accessed June 13, 2021.

[12] National Institutes of Health. COVID-19 treatment guidelines: Vitamin C. April 21, 2021. https://www.covid19treatmentguidelines.nih.gov/supplements/vitamin-c/. Accessed June 13, 2021.

[13] National Institutes of Health. COVID-19 treatment guidelines: Zinc. April 21, 2021. https://www.covid19treatmentguidelines.nih.gov/supplements/zinc/. Accessed June 13, 2021.