key: cord-0888575-bp1iww8s
authors: Rawat, Dimple; Roy, Avishek; Maitra, Souvik; Gulati, Arti; Khanna, Puneet; Baidya, Dalim Kumar
title: Vitamin C and COVID-19 treatment: A systematic review and meta-analysis of randomized controlled trials
date: 2021-10-28
journal: Diabetes Metab Syndr
DOI: 10.1016/j.dsx.2021.102324
sha: 716b5012cf9c0b76d1cea3509a67c446f7e07db1
doc_id: 888575
cord_uid: bp1iww8s

BACKGROUND AND AIMS: Vitamin C has been used as an anti-oxidant in various diseases including viral illnesses like coronavirus disease (COVID-19) METHODS: Meta-analysis of randomized controlled trials (RCT) investigating the role of vitamin C supplementation in COVID-19 was carried out. RESULTS: Total 6 RCTs including n = 572 patients were included. Vitamin C treatment didn't reduce mortality (RR 0.73, 95% CI 0.42 to 1.27; I(2) = 0%; P = 0.27), ICU length of stay [SMD 0.29, 95% CI -0.05 to 0.63; I(2) = 0%; P = 0.09), hospital length of stay (SMD -0.23, 95% CI -1.04 to 0.58; I(2) = 92%; P = 0.57) and need for invasive mechanical ventilation (Risk Ratio 0.93, 95% CI 0.61 to 1.44; I(2) = 0%; P = 0.76). Further sub-group analysis based on severity of illness (severe vs. non-severe), route of administration (IV vs. oral) and dose (high vs. low) failed to show any observable benefits. CONCLUSION: No significant benefit noted with vitamin C administration in COVID-19. Well-designed RCTs with standardized control group needed on this aspect.

The coronavirus (COVID-19) pandemic has wreaked havoc across the globe causing 226,844,344 cases till 14 th September, 2021 cases and nearly 4.7 crore deaths (1). This virus leads to increase in pro-inflammatory cytokines and acute serum biomarkers (CRP, ferritin, Ddimer etc) (2) . The initial viral cytopathic effects, followed later on by 'cytokine storm' may bring about major health related adverse effects like acute respiratory distress syndrome (ARDS) (3, 4) . Different anti-inflammatory interventions e.g. steroids, vitamins, micronutrients and immunomodulating agents have been tried till date. Vitamin C, also known as ascorbic acid, is well known for its anti-inflammatory and free radical scavenging properties (5, 6) . It may also augment vasopressor and cortisol synthesis, influence leucocyte functioning via neutrophil extracellular traps (NET), thereby strengthening the armamentarium against various pathogens including viruses (6) (7) (8) . Previously vitamin C has been shown to reduce mortality, vasopressor usage and organ failure in sepsis patients (9, 10) , however, larger randomized trials failed to show any major health benefits (11, 12) . Considerable controversy still exists regarding vitamin C supplementation among various systematic review and meta-analyses, owing to the The articles were screened for title and abstract initially using the pre-defined search strategy by DR and AR. Duplicates or any other irrelevant articles not meeting the inclusion criteria were removed, followed by full text screening for the final inclusion in the present review. Any disagreement regarding the article was sought by SM.

Relevant data including study design, setting, duration, disease severity, mode of administration, dose of the intervention, duration of the intervention, ICU length of stay, duration of hospital stay, mortality and IMV incidence were extracted by DR and AR for each article included in the review. To resolve the conflict SM was approached to reach a consensus. For converting data described in median (range) or median (Interquartile range) to mean (SD), appropriate validated methods by Luo (22) (23) (24) . Data were tabulated using excel (2019) spreadsheet.

Methodological quality was as per Cochrane Systematic Review Guidelines and GRADE-PRO approach was used for rating the quality of a body of evidence. The individual studies were evaluated separately AR and DR and in case of dilemma regarding quality assessment were resolved after discussion with SM.

Effect measure for variables described in rates/proportion (mortality, incidence of mechanical ventilation) was done by Risk Ratio (RR) and for continuous variables Standard Mean Difference (SMD) was used. I 2 was used to test the heterogeneity among the included studies. P-value less than 0.05 was considered to be statistically significant. Methodological quality was assessed using Review Manager software, version 5.4.

The initial search identified a total of 273 articles via database searching and 74 via manual searching. Authors of 7 trials were approached out of whom one replied with full published data (17) . After screening the title and abstract of all the retrieved articles followed by full text assessment a total of 6 articles were included in the final review ( Figure 1 ; Table 1 , 2 &3).

All included studies in the present review had randomization involving 572 subjects, ranging from 20 to 214 subjects (14) (15) (16) (17) (18) (19) . Among the six included studies three were from Iran (17) (18) (19) , one from China (14) , one from Pakistan(15) and one from United states (16) . Four studies were conducted on patients with disease severity as severe (14, 15, 17, 19) and two as non-severe (16, 18) . Route of administration was intravenous in fours studies (14, 15, 17, 19) and oral in two studies (16, 18) . Doses of vitamin C ranged from 50mg/kg/day (15) to 24g/day (14) . In one study (16) patients were randomized in a 1:1:1:1 allocation ratio (zinc gluconate: ascorbic acid: both: standard). In this review, these 4 groups were sub divided into two groups for the purpose of analysis i.e., group 1: standard care vs ascorbic only and; group 2: zinc and ascorbic vs zinc.

Risk of bias graph, review authors judgements about each risk of bias item are presented as percentages and risk of bias summary based on Cochrane Systematic Review Guidelines for each included study (green for low risk of bias, yellow for unclear risk of bias and red for high risk of bias) for randomised control trials is presented in figure 2a-2d; 3a-3b.

Random sequence generation: Among all, Hakamifard A et al., 2021 (18) was rated as high risk due to no true randomization, Darban M et al., 2021 (17) as unclear risk of bias because the method of randomization was not stated and rest four (14) (15) (16) 19) Allocation concealment: One study Zhang J et al., 2021 (14) was rated at low risk of bias, because the allocation was concealed adequately, the generated random list was stored by the principal investigator who was not involved in the treatment of patients and was hidden to the other investigators. Rest five were judged at unclear risk of bias (15) (16) (17) (18) (19) because either the method of allocation concealment was not mentioned (16) (17) (18) or it was unclear that who stored the generated random list (15, 19) . Zhang J et al., 2021(14) was rated at low risk of bias because both the participants and trial personnel were blinded, the subjects were enrolled in the corresponding group according to the chronological order of ICU recruitment; also the grouping and intervention were unknown to the participants and investigator. Hakamifard A et al., 2021 (18) did not mentioned the about blinding of participants and personnel hence was judged at unclear risk of bias. Rest four (15) (16) (17) 19) were open label trials hence, were judged at high risk of bias.

Blinding of outcome assessment (Detection bias): : Zhang J et al., 2021 (14) was judged at low risk of bias as the grouping and intervention were unknown to the participants and investigators who were responsible for data collection and statistical analysis. Remaining five studies (15) (16) (17) (18) (19) were judged as unclear risk for bias as the blinding of outcome assessment was not mentioned.

All included six studies (14) (15) (16) (17) (18) (19) reported data for all outcomes in results hence were judged at low risk of bias.

All included six studies (14) (15) (16) (17) (18) (19) were judged at low risk of bias for selective reporting.

The overall rating for the quality of evidence for the role of vitamin C supplementation in patients with COVID-19 is shown in the GRADE summary of finding table 4. GRADE summary reported the certainty of evidence as very low for the outcome duration of hospital stay and low for mortality, ICU admission and moderate for NIV incidence which means that any estimate of effect is very uncertain and we have little confidence in the effect. (Figure 2a-2d) 

Mortality was reported in five studies (14) (15) (16) 18, 19) , involving 552 subjects (276 intervention and 276 controls/placebo). In the pooled analysis, no statistically significant difference was observed as compared to controls/placebo (Risk Ratio 0.73, 95% CI 0.42 to 1.27; I 2 =0%; P=0.27) (Figure 2a ).

Three studies reported outcome ICU length of stay (14, 17, 19) involving 136 subjects (67 intervention and 69 controls/placebo). Pooled analysis did not show any statistically significant difference of the intervention for this outcome (SMD 0.29, 95% CI -0.05 to 0.63; I 2 =0%; P=0.09) (Figure 2b ).

Four studies reported duration of hospital stay (14, 15, 18, 19) . No statistically significant difference was observed in the pooled analysis (SMD -0.23, 95% CI -1.04 to 0.58; I 2 =92%; P=0.57) (Figure 2c ).

Three studies reported IMV incidence (14, 15, 19) . No statistically significant difference of the intervention for this outcome (Risk Ratio 0.93, 95% CI 0.61 to 1.44; I 2 =0%; P=0.76) was noted in the pooled analysis ( Figure 2d ).

Sub-group analysis was performed for various outcomes including mortality, ICU length of stay, duration of hospital stay and IMV incidence for vitamin C dose (High and low dose), mode of intervention (oral and IV) and severity of disease (severe and non-severe), but did not find any statistically significant difference for any of the outcome and/or sub-groups. Due to clear cut lack of definition of high dose of vitamin C, we used the cut off value of >10 gm/day as high dose, based on two previous studies (10, 25) . (Figure 4 to 7) 

The present meta-analysis showed that administration of vitamin C did not have any effect on major health outcomes in COVID infected patients, in comparison to either placebo/standard therapy. Sub-group analysis also revealed that irrespective of its dosage, route of administration and disease severity, it didn't have discernible benefit in such patients. The SARS-CoV-2 may cause a pro-inflammatory state evidenced by raised serum levels of Interleukin-1,6 (IL-1,6) and tumor necrosis factor (TNF) etc., which may in turn lead to 'cytokine storm' and ARDS (2, 26, 27) . Various vitamins, anti-oxidants and immunomodulators have been investigated to curtail the disease progression. Vitamin C has been known to possess free radial oxygen and nitrogen scavenging properties along with anti-inflammatory effects (5) . Ascorbate augments synthesis of catecholamines [cofactor of enzyme Dopa beta-hydroxylase, which convert Dopa(Dihydroxy phenyl alanine) to Dopamine] and vasopressin [cofactor of peptidylglycine alpha-amidating mono-oxygenase(PAM)] (8) . In experimental animal models, it reduced organ dysfunction secondary to abdominal sepsis and gram negative bacteraemia (28, 29) , highlighting its role in stabilising leucocyte & NK cell function (7). Meta-analysis of 9 trials which evaluated the effect of vitamin C in acute respiratory infections (ARI) showed that it reduced overall duration of symptoms and major complaints like chest pain and chills (30) . Various other case reports of high dose vitamin C halting disease progression in viral illnesses, highlighted its anti-viral properties (31) . In a retrospective propensity matched before after study carried out on (n=94) patients with severe septic shock with elevated serum procalcitonin (>2 microgram/ml) levels, combination therapy of 6 gm intravenous vitamin C (A), 200 mg hydrocortisone (H) and 400 mg thiamine (T) per day (HAT therapy) for 4 days reduced mortality by almost 5 times (8.5% with HAT therapy vs. 40.4% controls), as well as reduced vasopressor support, incidence of acute kidney injury (AKI) and serum procalcitonin levels (9) . In another phase I trial carried out on 24 patients, high dose (200 mg/kg/day) of IV vitamin C therapy showed promising results by reducing organ dysfunction (SOFA score) as compared to low dose(50 mg/kg/day) (10). This study also highlighted possible role of vitamin C in attenuating sepsis induced endotheliopathy evidenced by reduced thrombomodulin levels (10) . Another trial demonstrated reduction of dose and duration of vasopressor with 100 mg/kg/day of vitamin C therapy (32) . In burn patients (n=31) with >30% body surface involvement, vitamin C therapy reduced volume of resuscitation fluid volume, wound edema and respiratory dysfunction (33) . Despite its promising role in preventing organ failure in sepsis, large trials failed to demonstrate improvement in major health related outcomes. In VITAMINS trial involving 211 septic shock patients HAT therapy didn't reduce mortality or vasopressor free days as compared to hydrocortisone alone (11) . In a follow up phase II CITRIS-ALI trial on n=167 patients, vitamin C didn't reduce organ failure score and inflammatory markers, despite reduction in 28 day mortality (12) . In a meta-analysis of heterogenous group of studies including those carried out in ICUs (n=16) and cardiac surgery patients (n=28), vitamin C reduced ICU & hospital stay along with incidence of post-operative atrial fibrillation, without having any effect on mortality (34) . Although findings of our meta-analysis matches with that of Putzu et al (33) , we included only RCTs in COVID infected patients. In another meta-analysis that included majorly cardiac surgery patients (13 out of 18 included studies), vitamin C reduced length of hospital stay and mechanical ventilation without any mortality benefit (35) . In a meta-analysis evaluating the effect of IV vitamin C that included 12 RCT and quasi RCTs, no mortality benefit was noted at doses >10 gm/day and <3 gm/day, though, reduction of vasopressor support and mechanical ventilation was seen. Interestingly, they showed a medium dose (3-10 gm/day) had mortality benefit, although no biologically plausible explanation was provided (30) . In comparison to our study, their population were functionally heterogenous including patients receiving vitamin C for prevention of contrast induced nephropathy, which could have contributed to this finding.

A meta-analysis evaluating isolated effect of vitamin C on clinical outcomes showed reduced vasopressor dose and mechanical ventilation with similar mortality (36) . Findings of our study could be attributable to following reasons. Firstly, lack of universally accepted optimal dose and route of administration. Considering recommended dietary allowance of vitamin C to be 75-110 mg/day and a serum value of 50-70 micromole/L to be normal (<23 micromole/L deficient, <11 micromole/L very low) (37, 38) , as much as 40% ICU population may be vitamin C deficient, which in turn, is linked to excessive mortality (8, 39) . Oral absorption of ascorbate becomes erratic due to saturation of transporter proteins in critical illness, so much so, that around 3 gm of intravenous replenishment is needed for attaining normal serum values (40, 41) . Secondly, how 'high' should be considered high is not known. In this review, various dosages ranging from 1 to 24 gm/day have been used. For our convenience we assumed >10 gm/day as 'high' as in Fowler's study, 200 mg/kg/day (around 12 gm/day). Wang et al also used the similar operational definition (25) for 'high' dose. Thirdly, as previously seen with meta-analysis of other vitamins/antioxidants in COVID, a theoretical benefit may not always extrapolate in to clinical benefit, as deficiency in particular vitamin may merely mark a disease process rather than its outcome (42) . Lastly, prospective administration after diagnosis of COVID, may not be as useful as physiologically replenished state prior to contracting the disease, echoing the notion 'prevention is better than cure'.

Vitamin C therapy didn't reduce major health related outcomes in COVID patients. In subgroup analysis based on drug dose (high vs. low), route (IV vs. oral) and severity of illness (severe vs. non-severe) no significant benefit were observed. Hence, larger prospective randomized trials are needed in order to evaluate the effect of isolated vitamin C administration, separately for both vitamin C replete and deplete individuals. Treatment in the control group should be guided by prevailing standard of care for COVID infected patients.

There are various limitations of this study are. Firstly, heterogeneity of included population, drug dosages and route, which makes results inconclusive. However, sub-group analysis also revealed similar findings. Secondly combination therapy with other agents like vitamin E and melatonin etc. confounds our study finding, like it did in Marik's study (9) . Thirdly, the standard therapy in the control group were dissimilar, owing to their different period of completion. Steroids and anticoagulation have been considered as standard therapy for hospitalised patients requiring oxygen (43, 44) . However, included studies conducted during the initial period of COVID, administered steroids to minority (8-30%) of patients requiring oxygen (14, 15) . Fourth, due to lack of data, serious adverse events with high dose vitamin C could not be reported. Lastly, due to less number of studies (n<10) meta regression could not be performed. 

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Reports sought for retrieval (n=74)Reports not retrieved (n=05)