Vitamin C and zinc are commonly used to stave off or reduce the severity of colds and flu—but what's their effect on Covid-19? Findings from the first randomized clinical trial of the two supplements' effects on Covid-19 suggest "unimpressive" results, Sandee LaMotte writes for CNN.

Background

According to CNN, many people use vitamin C and zinc supplements in an effort to combat viral colds and the flu—and past research suggests these supplements can be modestly helpful in reducing the length of these common infections.

For instance, supplements of vitamin C, an antioxidant that provides critical support to the immune system, have been shown to shorten the duration of colds by 8% among adults and by 14% among children—although taking the supplement doesn't appear to prevent illness, nor does taking it after symptoms begin seem to help.

Similarly, a literary review of zinc—which plays a key role in regulating metabolism and the immune system—found that if the supplement is taken within 24 hours of when cold symptoms first present, it may cut the length of a cold by a day. 

More recently, researchers have started to explore whether the supplements can protect against Covid-19, or at least reduce the severity of infection.

Early research conducted last year found that among hospitalized Covid-19 patients, each unit increase in zinc-blood level was associated with a 7% lower risk of in-hospital death—although the researchers looked only at levels of zinc in patients' blood, not the effects of zinc supplementation.

Separately, a retrospective observational study of hospitalized Covid-19 patients found that patients treated with zinc in combination with the antimalaria drug hydroxychloroquine and the antibiotic azithromycin were less likely to die or be transferred to hospice care when compared with patients who received the other drugs but not zinc. However, the study was not a randomized controlled trial, so it could not determine whether zinc actually caused the observed reduction in risk.

New findings

For the latest study, published in JAMA Network Open, researchers divided 214 study participants, all of whom were recovering from Covid-19 at home, into four groups. One group received gave high doses of zinc, the second group got high doses of vitamin C, and the third group received high doses of both drugs. The fourth group acted as a control, receiving only standard care such as rest and fever-reducing drugs.

Ultimately, the researchers found the supplements provided no benefit to study participants. In fact, the results were so "unimpressive," LaMotte reports, that the researchers ended the study early.

"Unfortunately, these 2 supplements failed to live up to their hype," Erin Michos, an associated professor of medicine at John Hopkins University School of Medicine, and Miguel Cainzos-Achirica, an assistant professor of preventive cardiology at Houston Methodist, wrote in an editorial accompanying the study. Further, they noted that the high doses of the supplements were linked to unpleasant side effects, including "nausea, diarrhea, and stomach cramps."

However, according to LaMotte, other researchers are still investigating potential effects of these and other supplements in preventing or treating Covid-19, with studies in progress on vitamin C, vitamin D, and zinc (LaMotte, CNN, 2/12).