Vitamin C and zinc lozenges for COVID-19?

To the Editor:

We share Marwitz’ concerns regarding widespread misinformation about coronavirus disease 2019 (COVID-19) treatments. However, we do not agree with the statement that "Past examples of vitamin C and zinc, marketed for common cold symptoms, make extensive claims about treating and curing common colds, but the data do not fully support safety and efficacy of these agents.2, 3, 4 Ironically, these agents are being promoted as unsubstantiated treatments or preventives for COVID-19 today."

In our Cochrane review, we found that regular vitamin C supplementation of at least 0.2 g/d shortened the duration of viral respiratory tract infections in adults by 7.7% (P < 0.001) and in children by 14.2% (P < 0.001). Our review supports the safety and efficacy of vitamin C. We did not demonstrate an effect when vitamin C was administered as a treatment, but low doses, short treatment, and late treatment may explain negative findings. Vitamin C may also have an effect on COVID-19, and a recent randomized trial observed that vitamin C increased the recovery rate of outpatients infected with severe acute respiratory syndrome coronavirus 2 by 70%.

Marwitz refers to a zinc review; however, the review is flawed. There is strong evidence that appropriately composed zinc lozenges can shorten the duration of respiratory virus infections.8, 9, 10, 11 Unfortunately, many of the zinc lozenges on the U.S. market contain either doses of zinc which are too low or substances that bind zinc ions so tightly that they are ineffective.

There is much misinformation about vitamin C and zinc in popular forums and also, unfortunately, in scientific forums , 6, 7 , 12, 13, 14, 15; however, the positive findings from randomized trials should not be ignored.