Vitamin C, a natural antioxidant and potent free radical scavenger, has long been known for its antiviral effect [60]. The capacity for donating electrons enables vitamin C to support essential cellular processes and immune responses [61–64]. Vitamin C maintains barrier integrity and facilitates wound healing of the skin against oxidative stress and microbial infections [65,66]. Vitamin C is required for chemotaxis, phagocytosis, and microbial clearance in neutrophils [67,68]. It is also necessary for apoptosis and clearance of used neutrophils as well as neutrophil extracellular trap (NET) formation [69,70]. The acidic condition caused by vitamin C helps to convert inorganic nitrate into NO [71]. Lack of vitamin C leads to immune dysfunction and vulnerability to infection. Humans cannot produce vitamin C owing to nonfunctional L-gluconolactone oxidase. Supplementation with a high dose of vitamin C can reduce the symptoms and duration of the common cold [72]. Vitamin C therapy is recognized as a beneficial adjunctive strategy to ameliorate the symptoms of respiratory diseases, including severe acute respiratory disease (SARS) [73]. Glucose competes with the uptake of the oxidized form of vitamin C, dehydroascorbic acid, via the glucose transporter [74]. Hence, the bioavailability of vitamin C can be restricted by hyperglycemia. If diabetic COVID-19 patients have low levels of vitamin C and are not treated with intravenous vitamin C, it may partly explain the severity of their illness. Several clinical trials have been proposed to infuse high dose vitamin C as an intervention for COVID-19 patients [75].