Vitamin C for COVID-19 treatment may benefit some populations

High doses of vitamin C for treating the novel coronavirus (COVID-19) may benefit some populations, but researchers said factors that influence effectiveness include levels of the natural transporter needed to get the vitamin inside cells, according to a new study by researchers at the Medical College of Georgia Center for Healthy Aging and published in the journal Aging and Disease.

Vitamin C is an essential vitamin. Foods naturally high in vitamin C include oranges, potatoes, tomatoes, broccoli, and Brussels sprouts. The vitamin's diverse roles in the body also include formation of blood vessels, collagen, and cartilage, the researchers said.

The novel nature and lack of immunity against the coronavirus has prompted a worldwide pursuit of effective treatments for COVID-19, the researchers said. That includes repurposing drugs with known safety profiles, including vitamin C, an established immune system booster and antioxidant, which made it a logical choice to explore in COVID-19. Both strategies are needed in response to infection with the novel coronavirus to ensure a strong immune response to stop the virus from replicating in the body, and to avoid the over-the-top, destructive immune response the virus itself can generate if it does, according to the study.

There are at least 30 clinical trials underway in which vitamin C, alone or in combination with other treatments, is being evaluated against COVID-19, some with doses up to 10 times the recommended 65 to 90 milligrams daily of vitamin C. Factors like whether or not vitamin C can get inside the cell, likely are an issue in the effectiveness the therapies ultimately show, the researchers said.  

Without adequate transporters on a cell's surface to get the water-soluble vitamin past the lipid layer of cell membranes, particularly large doses may enable the vitamin to cluster around the outside of cells where it actually starts producing oxidants, like damaging reactive oxygen species, rather than helping eliminate them, the researchers said.

The researchers said they suspect low transporter expression is a factor in the mixed results from vitamin C's use in a variety of other conditions. Clinical trials in osteoarthritis, for example, has gotten mixed results, they said. However its usage in other viral-induced problems, like potentially deadly sepsis, has shown benefit in reducing organ failure and improving lung function in acute respiratory distress syndrome, which is also a major cause of sickness and death with COVID-19.

Some conditions, like osteoarthritis, are associated with significant downregulation of at least one subtype of vitamin C transporter, the researchers said. Part of the concern with COVID-19 is that those most at risk mostly have both lower levels of vitamin C before they get sick and fewer transporters to enable the vitamin to be of benefit if they get more.

Many of those most at risk from COVID-19, including individuals who are older, Black, male and with chronic medical conditions like osteoarthritis, hypertension and diabetes, tend to have lower levels of vitamin C, another reason vitamin C therapy would be considered a reasonable treatment, the researchers said. The investigators also note that patients may develop a vitamin C deficiency over the course of their COVID-19 illness since, during an active infection, vitamin C is consumed at a more rapid rate. Insufficient levels can augment the damage done by an overzealous immune response, they said.

Low vitamin C levels also have been correlated with higher mortality in older individuals from causes like cardiovascular disease. High oxidative stress, a major factor in conditions like cardiovascular disease as well as aging and now COVID-19, also is associated with significantly reduced expression of the vitamin C transporter.

Age, race, gender, as well as expression levels and genetic variations of those vitamin C transporters that make them less efficient, all may be factors in the effectiveness of vitamin C therapy against COVID-19 and other maladies, the researchers said.

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