High doses of vitamin C under study for treating COVID-19 may benefit some populations, but investigators exploring its potential in aging say key factors in effectiveness include levels of the natural transporter needed to get the vitamin inside cells.
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, investigators at the Medical College of Georgia Center for Healthy Aging report in a commentary in the journal Aging and Disease.
The investigators recommend that those factors be considered in the design and execution of clinical trials, and when trial results are analyzed, for COVID-19 as well as other conditions, says Dr. Sadanand Fulzele, aging researcher and the article’s corresponding author.
The novel nature and lack of immunity against the coronavirus has prompted a worldwide pursuit of effective treatments for COVID-19, they write. 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.
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, says Dr. Carlos M. Isales, co-director of the MCG Center for Healthy Aging and chief of the MCG Division of Endocrinology, Diabetes and Metabolism.
In fact, 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, says Isales, a study coauthor.
“We think it’s important to look at transporter expression,” Fulzele says.
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, an autoimmune disease where a misdirected immune system is attacking the joints, has gotten mixed results, Fulzele says. 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.
At the time their Aging and Disease paper was published, there were not yet published studies of the efficacies of high-dose, intravenous vitamin studies underway for COVID-19.
Fulzele, who works on vitamin C in aging, and others have shown that some conditions, like osteoarthritis and even normal aging, are associated with significant downregulation of at least one subtype of vitamin C transporter.
In fact, part of the paradox and 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…