Vitamin D isn't an effective COVID-19 treatment, but scientists haven't ruled out its relationship to severe disease

• Zinc, vitamin C, and vitamin D don't prevent COVID-19 deaths, a scientific review found.
• But vitamin D shortened patients' hospital stay if they started taking it after getting COVID-19.

Scientists have wondered since the start of the pandemic whether certain vitamins like zinc, vitamin C, or vitamin D improve outcomes for COVID-19 patients. Globally, some doctors continue to prescribe these supplements in hopes of promoting a healthy immune response.

But a scientific review from the University of Toledo published last month found no evidence that taking zinc, vitamin C, or vitamin D reduces the risk of dying from COVID-19.

The analysis looked at 26 peer-reviewed studies from around the world that encompassed more than 5,600 hospitalized COVID-19 patients. Patients who took zinc and vitamin C did so after they were admitted to the hospital. The study also included patients who took vitamin D before their COVID-19 diagnoses, as well as some who took the supplement after they got sick.

Across all of these scenarios, vitamins didn't seem to lower the risk of mortality.

But vitamin D reduced the length of a person's hospital stay if they started taking the supplement after their COVID-19 diagnosis, whereas zinc and vitamin C did not.

Dr. Azizullah Beran, the study's lead researcher and a resident at the University of Toledo, said more studies are needed to know if vitamin D is an effective COVID-19 treatment.

"If it showed benefit in patients with normal vitamin D levels, then for sure you can say, 'Oh, vitamin D works,'" Beran said.

For now, he added, only patients who are deficient in these vitamins should take them as supplements.

Vitamins might offer immune support, but they don't treat COVID-19

Scientists often study zinc, vitamin C, and vitamin D in relation to viral infections.

Some research suggests that zinc might prohibit viruses from replicating, and populations at high risk of acquiring viruses like HIV or hepatitis C are often deficient in zinc. Vitamins C and D also have anti-inflammatory properties that may help ward off severe disease.

Based on this knowledge, Beran said, some countries have promoted "vitamin cocktails" for COVID-19. Early in the pandemic, Egypt required doctors to prescribe vitamin D, vitamin C, and zinc to symptomatic COVID-19 patients.

"At that time, there was no enough evidence for that, but they just made this conclusion based on non-COVID data," Beran said.

As of August 2021, Egypt's COVID-19 treatment protocol still included zinc and vitamin C. India also commonly prescribes vitamin C, vitamin D, and zinc for COVID-19, according to a June 2021 editorial in The Lancet.

But the National Institutes of Health has found "insufficient evidence" to support vitamin C, vitamin D, or zinc as COVID-19 treatments.

Beran said some patients in his Ohio clinic still believe vitamins will improve their COVID-19 symptoms.

There's no evidence for those beliefs, either: A February 2021 study found that zinc and vitamin C supplements neither reduced COVID-19 symptoms nor led to faster recovery.

Taking too much of a supplement can also result in unnecessary, and sometimes dangerous, side effects. High doses of vitamin C may cause diarrhea and nausea, while high doses of vitamin D may cause nausea, vomiting, kidney injury, or pancreatitis.

COVID-19 patients who are vitamin-deficient may benefit from supplements

Beran's study didn't consider whether hospitalized patients were deficient in certain vitamins before they got sick. For COVID-19 patients with vitamin deficiencies, taking supplements could help their immune system, but that's not the same as a direct treatment for COVID-19.

"There is strong data about the association of vitamin D deficiency and worse outcomes of COVID-19," Beran said, adding, "If someone has vitamin D deficiency, his immune system is not going to be as good as a patient with normal vitamin D."

A September 2020 study found people with vitamin D deficiencies had an increased risk of testing positive for COVID-19. A recent Israeli study also found that about half of people who were vitamin D deficient before getting COVID-19 developed severe illness, compared to less than 10% of people who had sufficient levels of the vitamin in their blood.

At the very least, Beran said, patients with vitamin deficiencies should take supplements to restore these essential nutrients.

"If someone is admitted with COVID and, incidentally, you found that the patient had severe vitamin D deficiency, of course treating that patient with vitamin D will help," he said.

Vaccines remain our most important tool for preventing severe COVID-19, he added, and steroids our most effective method of treating it. After two weeks, booster shots reduced the risk of COVID-19 hospitalization by at least 90%, according to data from the Centers for Disease Control and Prevention.