Despite their reputation for boosting the powers of your immune system, a new study reports that vitamin C and zinc supplements don't help COVID-19 patients recover from their illness.

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Giving one or the other, or a combination of both, to patients didn't significantly reduce the severity or duration of their COVID-19 symptoms. Zinc is important for immune function, and vitamin C is an antioxidant shown to boost the immune system.

In this study, researchers assessed how 214 adults with confirmed COVID-19 infection responded to either: 10 days of zinc gluconate (50 milligrams/mg), vitamin C (8,000 mg), both, or usual care.

The study, which had an endpoint of a 50% reduction in symptoms, was conducted from April to October 2020. It was halted early because there were no significant differences between the four groups of patients.

The findings were published Feb. 12 in the journal JAMA Open Network.

"When we began this trial, there was no research to support supplemental therapy for the prevention or treatment of patients with COVID-19," said study author Dr. Milind Desai, director of clinical operations at Cleveland Clinic's Heart, Vascular & Thoracic Institute.

"As we watched the pandemic spread across the globe, infecting and killing millions, the medical community and consumers alike scrambled to try supplements that they believed could possibly prevent infection, or ease COVID-19 symptoms, but the research is just now catching up," Desai said in a Cleveland Clinic news release. "While vitamin C and zinc proved ineffective as a treatment when clinically compared to standard care, the study of other therapeutics continues."

The patients in this study weren't hospitalized, but they received outpatient treatment.

"We know that not all patients with COVID-19 require hospital admission, and compared to those being treated in a hospital setting, they are more likely to be seeking out supplements that could help them, so it was an important population to study," said study co-author Dr. Suma Thomas, vice chair of strategic operations at the institute.