Vitamin C, Anti-Infective Immunity and the Issue of Decreased Vitamin C Levels in Children

Results: In the Department of Pediatrics of Ostrava-Vítkovice Hospital (Czech Republic), study investigators identified, 23% children with the most severe level of vitamin C deficiency in the urine (1 mg/dL), with the levels of vitamin C deficiency of 10 mg/dL, 20 mg/dL and 50 mg/dL diagnosed in 41%, 11%, and 14% of children, respectively whereas full tissue vitamin C saturation (100 mg/dL) was found in only 11% of children. Thus, overall, 75% of children had appreciable vitamin C deficiency with only 25% of children showing relatively adequate tissue vitamin C saturation. On admission and during hospitalization, 59% of pediatric patients were on pharmacotherapy; of these, 18% were diagnosed with severe vitamin C deficiency at a level of 1 mg/dL, with the levels of vitamin C deficiency of 10 mg/mL, 20 mg/mL and 50 mg/mL determined in 43%, 9% and 16% of children, respectively. Adequate vitamin C saturation was found in only 14% of the children. The same tests performed in the Department of Pediatrics of Olomouc University Hospital revealed decreased vitamin C levels in 98% of hospitalized pediatric patients.


Vitamin C and anti-infective immunity
Vitamin C is a substance essential for humans at all stages of their growth and development. It is necessary for physiological development during ontogenesis, as well as for the proper functioning of all body systems in childhood, adolescence and adulthood [1]. The importance of adequate vitamin C supply for the immune system to work properly has long been empirically known. Individuals with inadequate vitamin C intake are not only susceptible to frequent infections, but the course of infectious diseases is more serious, and there is an increased risk of developing a variety of chronic conditions [2]. A critical role in antibacterial immunity is played by the barrier function, primarily that of the mucous membrane. Sufficient vitamin C levels are also critical for adequate functioning of all types of leukocytes (including their migration, ability to destroy pathogens and apoptosis of exhausted cells). Under normal conditions, vitamin C levels in these cells are more than a hundred-fold higher compared with those in plasma.
Antimicrobial immunity involves phagocyte migration to the focus of the infection and, once phagocytosis of microbes has occurred, apoptosis of exhausted cells. The local antigen-presenting cells transfer the information about the pathogen to regional memory T cells, which exert cytotoxic action on bacteria followed by activation of B cells transforming to plasma cells to produce antibodies. Other types of cells involved in antibacterial immunity include Th1 cells which activate bacteria-killing macrophages, and Th2 cells, which stimulate B cells to produce antibodies. Proper functioning of these cells requires sufficient levels of vitamin C [2].
Likewise, efficient antiviral immunity requires adequate vitamin C levels., as does the important role played by the barrier function. The cornerstone of innate antiviral immunity is interferon (type I IFN), which most cells begin to produce upon viral invasion.
An important component of non-specific antiviral immunity is NK (natural killer) cells. Phagocytosis of viruses is a major function performed primarily by macrophages. An efficient antiviral tool in this respect are antibodies produced by B cells. As to cell type-specific immunity, the most important players are cytotoxic CD8+ T cells.
For all these components of antiviral immunity to work properly, sufficient supply of vitamin C is perquisite [2]. Given the significant effect of vitamin C on the immune system, its deficiency results in increased susceptibility to infectious diseases, which worsens the deficiency due to increased vitamin C consumption. As shown by various studies, patients with acute respiratory conditions, such as bronchopneumonia, often develop vitamin C deficiency [3]. Vitamin C supplementation in patients with respiratory tract infections will eliminate the deficiency and help improve the clinical prognosis [4].
Vitamin C deficiency, which frequently precedes the development of infectious diseases, further deteriorates during the course of the disease per se because of the increased vitamin C consumption due to more intensive metabolism in the presence of inflammation. This is also why the demand for vitamin C supplementation as part of management of infectious diseases is substantially higher than preventive doses. For example, several studies have shown that vitamin C reduced the viral load in cells infected by Epstein-Barr virus (EBV) [5] or cytomegalovirus (CMV) [6].
Vitamin C significantly enhances chemotaxis and the phagocytic potential of neutrophils, i.e., oxidative destruction of pathogens in those cells while promoting lymphocyte proliferation and functioning [7,8]. Vitamin C deficiency results -when the body is exposed to the action of a virus -in high viral titers in the lungs and a decrease in the levels of the cytokines with antiviral action, particularly interferons alpha and beta (IFN-α/β) [9]. Moreover, vitamin C deficiency is associated with increased production of anti-inflammatory cytokines such as tumor-necrosis factor (TNF) and interleukin-1 (IL-1) in the lungs. Once vitamin C deficiency has been eliminated, these detrimental processes cease. Studies have shown that vitamin C deficiency results in the formation of inflammatory lesions in the lungs when exposed to a viral infection (e.g., influenza), [10] whereas vitamin C supplementation has a beneficial effect on the health status of lungs in individuals with viral pneumonia [11]. The antiviral action of ascorbate has been documented with a host of viruses such as respiratory syncytial virus (RSV) [12][13][14].

Decreased vitamin C levels and options for their detection and vitamin C supplementation Worldwide Incidence of Decreased Vitamin C Levels
Normal serum vitamin C levels are commonly defined as values above 28 micromoles/L (μmol/L) with concentrations between 11 and 28 μmol/L considered hypovitaminosis (suboptimal levels); levels lower than 11 μmol/L are referred to as vitamin C deficiency.
Given the above, values below 28 μmol/l are considered decreased vitamin C levels [15]. There is a general notion that low vitamin C levels in developed countries are a rare occurrence; regrettably, this is a common misconception. The incidence of decreased tissue vitamin C saturation is certainly not confined to developing regions, such that it affects, for example, 70% of the Ugandan population [16]. Quite surprisingly, vitamin C deficiency is frequently encountered in industrialized nations despite the general awareness and promotion of a healthy diet and the wide availability of vitamin C-containing foods and dietary supplements. Surveys have reported insufficient vitamin C intake in an approximately 20% of the European population [17]. The third Glasgow MONICA population survey documented vitamin C deficiency in 14% of women and 26% men in Scotland [18]. A Canadian survey reported decreased vitamin C levels in almost half of the population, a finding correlating with higher rates of inflammatory diseases [15]. The prevalence of decreased vitamin C levels across Europe has been estimated at The surprisingly high prevalence of decreased vitamin C levels even in developed countries is supported by a survey conducted in the USA and showing decreased (suboptimal) vitamin C levels in about one in five of those surveyed and severe vitamin C deficiency in 10% of the general population, with the implication being that about one in three Americans suffer from vitamin C deficiency. The aforementioned survey again confirmed a correlation between vitamin C deficiency and increased levels of inflammatory markers and other risk factors such as overweight, obesity and metabolic syndrome. As an important observation emerging from the survey, its authors suggest that the cause of decreased tissue saturation with vitamin C is not only due to lower dietary intake but, also, diseases involving oxidative stress associated with increased utilization of ascorbate thus causing a decrease in systemic vitamin C levels [20]. Although the rates of decreased plasma vitamin C levels in children in developed regions of the world seem to be lower compared with adults, studies show that a limited intake of this vitamin (e.g., in underprivileged individuals) is associated with increased rates of vitamin C deficiency. This is exemplified by the pediatric population in Mexico where suboptimal vitamin C levels and deficiency were reported in 38% and 23% of children, respectively; hence, decreased vitamin C levels are present in over 60% of the children assessed. And again, a correlation was observed between decreased vitamin C levels and the incidence of overweight and obesity [21,22].
Case reports published in the USA suggest that severe vitamin C deficiency with symptoms of scurvy is not a rare occurrence even in children. Vitamin C deficiency is found most often in children with chronic conditions such as food allergies, malabsorption, renal failure, neurologic and psychiatric (e.g., autism spectrum) disorders or cancers. The cause of the deficiency may be, in some social strata, inadequate intake of vitamin C-rich foods due to excessively permissive education, religious habits, or even incorrectly defined diet composition. Factors potentially contributing to vitamin C (and, hence, its deficiency) may include use of some classes of drugs such as barbiturates [23,24]. The main factor determining tissue saturation with vitamin C is its oral intake, whether that be from the diet itself or from use of dietary supplements. As shown by earlier surveys, individuals of higher social standing who take dietary supplements containing vitamin C have a substantially lower risk of developing vitamin C deficiency. Vitamin C content in one´s diet is determined by its composition and processing; thermal processing (e. g. cooking) is known to destroy vitamins.
Tissue vitamin C saturation is further affected by environmental factors such as climate, season of the year, and place of residence.
Pollution is another important factor which increases oxidative stress and, hence, the need for vitamin C supplementation. Other factors include demographic variables such as age and sex, plus socioeconomic factors such as social standing, education level, lack of access to vitamin C-rich foods and others. In addition, vitamin C levels are impacted by concurrent diseases, primarily chronic conditions associated with inflammation (e.g., infection), which as a consequence, precipitate the development of oxidative stress and increased vitamin C utilization [25,26].

Preliminary Evaluation of Vitamin C Deficiency
Since clinical signs of oxidative stress do not manifest themselves until the deficiency has become severe, it is appropriate to utilize methods which will detect vitamin C deficiency earlier.
Identifying at-risk individuals, such as children treated on an out-patient basis or hospitalized, will help determine the extent of vitamin C supplementation necessary. One option to ascertain serum vitamin C levels is to use liquid chromatography, but this and other currently available techniques are relatively accurate, they are costly, time-consuming and require well trained staff and appropriately equipped centers. A technique deemed suitable for preliminary assessment of tissue vitamin C saturation ascertains vitamin C levels in the urine; it is based on the reaction of a chelating agent with a polyvalent metal ion to form a chelate complex. As the dipstick test strip changes color, it is matched to the corresponding color on the provided color chart. The results offer preliminary information about any level of vitamin C deficiency. The values measured in the urine correlate with the plasma vitamin C levels and, by association, its tissue saturation [27].

Options in Oral Supplementation
In healthy children with normal vitamin C saturation, the

Vitamin C saturation in children living in the Ostrava region Patients and Methodology
In 2019, a group of 150 children underwent preliminary assessment of urinary vitamin C levels in the Department of Pediatrics of Agel Hospital in Ostrava-Vítkovice. The group included 54% females and 46% males aged less than 18 years.
The overwhelming majority of patients were those with acute respiratory tract infections (pharyngitis, laryngitis, bronchitis, bronchopneumonia) followed by (in terms of frequency) children with inflammatory bowel disease (mostly acute gastroenteritis) and kidney disease (acute pyelonephritis). Vitamin C levels were determined using test strips to assess ascorbic acid levels in the

Results
The preliminary assessment of vitamin C levels in the urine The most severe deficiency (1 mg/dL) was diagnosed in 34 children, of which half were below 6 years of age. On admission to hospital, these patients were more likely to use antibiotics, or had no medication use at all. Results of assessment of vitamin C levels in the urine using the Uro C Kontrol test strips in children enrolled in the above subgroups are shown in Table 1.    Overall, our survey revealed a marked prevalence of children with decreased vitamin C saturation, a condition which increases the risk of improper functioning or a disorder involving the immune, nervous or other systems, which may potentially result in reduced resistance to stress, increased susceptibility to respiratory tract infections and, generally, inflammatory conditions associated with oxidative stress. Hence, it is imperative to provide adequate vitamin C supplementation in children with decreased vitamin C saturation to ensure the proper functioning of all body systems.
The best source of vitamin C continues to be a varied diet, rich in vegetables and fruits; however, as shown by our study, dietary vitamin C intake, in a big proportion of our pediatric population remains fairly inadequate and below the recommended values.