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March 2021

COVID-19: First Clinical Trials on Zinc, Vitamin C, Vitamin D

Previous reports claiming vitamin D, vitamin C and zinc might benefit COVID-19 outcomes were based on anecdotal evidence and observational data. We finally have randomized controlled trials evaluating these theories. Here’s what you should know.

Taking vitamin C and/or zinc by mouth doesn’t seem to speed up recovery from COVID-19 in non-hospitalized patients. A new study included 214 adult patients diagnosed with COVID-19 in outpatient care settings in Ohio and Florida. Patients were randomized to receive 50 mg of zinc gluconate, 8000 mg of vitamin C, both supplements, or standard care for 10 days. The study was stopped early because there was no apparent benefit from taking vitamin C and/or zinc. There were also notable side effects from high-dose vitamin C, such as diarrhea and severe stomach cramps.

Negative results were also seen in a new study evaluating vitamin D. Taking a single large dose by mouth doesn’t appear to improve outcomes in hospitalized patients. The new study included 240 moderately to severely ill patients with COVID-19. Patients were randomized to receive 200,000 IU of vitamin D in a single dose or placebo. Regardless of baseline vitamin D status, the single dose of vitamin D did not reduce the length of hospital stay, nor did it affect the mortality rate while in the hospital.

If patients ask about taking vitamin C, zinc or vitamin D for treating COVID-19, explain that we now have clinical data showing that none seem to speed up recovery. If patients still insist on taking these supplements, make sure they stick to USP verified products. Patients can get their recommended dietary allowance of zinc from food or supplements. Taking vitamin C 1-2 grams daily likely won’t cause any harm, and 400-1000 IU daily of vitamin D should result in adequate vitamin D levels for most people. But remind patients that taking high doses of vitamin C long-term isn’t necessary and can lead to complications such as increased kidney stone risk for some people.

For more information about natural medicines and COVID-19, see our latest articles and resources.

The information in this brief report is intended for informational purposes only, and is meant to help users better understand health concerns. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions. Copyright © 2021 Natural Medicines Inc. Commercial distribution or reproduction prohibited. Natural Medicines is the leading provider of high-quality, evidence-based, clinically-relevant information on natural medicine, dietary supplements, herbs, vitamins, minerals, functional foods, diets, complementary practices, CAM modalities, exercises and medical conditions. Monograph sections include interactions with herbs, drugs, foods and labs, contraindications, depletions, dosing, toxicology, adverse effects, pregnancy and lactation data, synonyms, safety and effectiveness.