Abstract
From Pauling’s theories to the present, considerable understanding has been acquired of both the physiological role of vitamin C and of the impact of vitamin C supplementation on the health. Although it is well known that a balanced diet which satisfies the daily intake of vitamin C positively affects the immune system and reduces susceptibility to infections, available data do not support the theory that oral vitamin C supplements boost immunity. No current clinical recommendations support the possibility of significantly decreasing the risk of respiratory infections by using high-dose supplements of vitamin C in a well-nourished general population. Only in restricted subgroups (e.g., athletes or the military) and in subjects with a low plasma vitamin C concentration a supplementation may be justified. Furthermore, in categories at high risk of infection (i.e., the obese, diabetics, the elderly, etc.), a vitamin C supplementation can modulate inflammation, with potential positive effects on immune response to infections. The impact of an extra oral intake of vitamin C on the duration of a cold and the prevention or treatment of pneumonia is still questioned, while, based on critical illness studies, vitamin C infusion has recently been hypothesized as a treatment for COVID-19 hospitalized patients. In this review, we focused on the effects of vitamin C on immune function, summarizing the most relevant studies from the prevention and treatment of common respiratory diseases to the use of vitamin C in critical illness conditions, with the aim of clarifying its potential application during an acute SARS-CoV2 infection.
Highlights
Vitamin C plays an important role in the normal functioning of the immune system [1,2,3,4] and its use in preventing and/or treating infections has strongly attracted the interest of physicians and investigators for almost a century
non-communicable diseases (NCDs) include obesity, diabetes mellitus, chronic lung diseases, cardiovascular diseases (CVD) and various other conditions which are characterized by systemic inflammation which impairs immune response and may exacerbate the cytokine storm related to COVID-19 [173, 174]
Apart from some specific individuals and conditions (Table 1), the evidence described is insufficient to support the efficacy of a regular supplementation with vitamin C for the prevention or treatment of the common cold or pneumonia in the general population
Summary
Vitamin C (ascorbic acid) plays an important role in the normal functioning of the immune system [1,2,3,4] and its use in preventing and/or treating infections has strongly attracted the interest of physicians and investigators for almost a century. Sepsis is a lifethreatening organ dysfunction caused by an impaired host response to infection, characterized by a dramatic failure of the circulatory, metabolic, and immune systems, and recognized as the primary cause of death from infection: patients who develop septic shock can have hospital mortality rates of up to 50% [22] On these clinical conditions literature shows that high doses of vitamin C by intravenous infusion may reduce the inflammatory cytokine-related production and potentially improve important outcomes such as the duration of mechanical ventilation time and mortality rates [13,14,15,16,17,18]. The aim of this review is firstly to summarize the immunological role of vitamin C with a description of its potential effects as a dietary supplement, on the mechanisms involved during respiratory viral infections, and in relation to the inflammatory response considering different subject categories and clinical conditions; secondly, the manuscript describes the updated literature on the IA of vitamin C in the treatment of severe sepsis and ARDS conditions, with the aim of establishing whether the current clinical background on this topic offers strong enough perspectives to propose vitamin C for a pharmacological application to reduce the dramatic cytokine production and regulate other recognized COVID-19-related immune responses
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