Investigating the effect of vitamin C supplementation on bacterial vaginosis: A systematic review and meta-analysis

Abstract

Bacterial vaginosis (BV), the most common type of vaginitis, results from reduced vaginal lactobacilli and increased anaerobic bacteria. Vitamin C may aid BV treatment by promoting lactic acid production. This study evaluated the effectiveness of vitamin C in treating BV. To this aim, a systematic search of PubMed, Scopus, Web of Science, and Iranian databases identified randomized clinical trials published up to October 29, 2024. The protocol for this systematic review is registered. Risk of bias was assessed using the Verhagen tool. Mean differences and their 95% confidence intervals (CIs) were calculated using the random-effects model. The quality of the evidence was evaluated with GRADEpro Guideline Development Tool, and statistical analyses were conducted using Review Manager (RevMan v5.3). Substantial heterogeneity (I² >50%) prompted the use of the random-effects model, subgroup analyses, and sensitivity analyses to investigate its origins. The meta-analysis included six randomized controlled trials of varying quality. Vitamin C showed a nonsignificant positive effect on the Whiff test (relative risk [RR] =1.19, 95% CI: 0.97–1.47, P = 0.09) but significantly improved vaginal pH < 4.5 (RR = 1.57, 95% CI: 1.21–2.03, P = 0.0006). While no significant reduction in vaginal discharge was observed (RR = 1.23, 95% CI: 0.94–1.60, P = 0.13), vitamin C significantly reduced the number of clue cells (RR = 1.34, 95% CI: 1.06–1.68, P = 0.01). Based on these findings, vitamin C supplementation may aid in achieving a vaginal pH < 4.5 and reducing clue cells in BV. However, further large-scale studies are warranted to confirm these results and elucidate the underlying mechanisms.

Introduction

Bacterial vaginosis (BV) involves a dysbiotic shift in vaginal flora, marked by a decline in hydroben peroxide-producing Lactobacillus species (such as Lactobacillus crispatus and Lactobacillus jensenii) and an overgrowth of anaerobic bacteria, including Gardnerella vaginalis and Mobiluncus mulieris.[1] BV is characterized by a homogeneous gray vaginal discharge with increased volume. The discharge typically has a pH >4.5 and emits an ammonia-like odor upon addition of 10% potassium hydroxide (Whiff test). Microscopic examination can reveal the presence of clue cells, characterized by epithelial cells coated with Gram-negative coccobacilli.[2] The condition is a common vaginal infection, affecting nearly one in three women.[3] BV is prevalent among reproductive-aged women, affecting 23% to 29% depending on the region: Europe (23%), East Asia (24%), Latin America (24%), Middle East (25%), Sub-Saharan Africa (25%), North America (27%), and South Asia (29%).[4]

Untreated or inadequately managed BV can lead to complications such as pelvic inflammatory disease, infertility, endometritis, and an increased risk of HIV acquisition.[5,6] Metronidazole remains the first-line treatment, administered in various regimens.[7] However, recurrence rates are high, reaching up to 80% within 9 months post-treatment. Possible reasons for recurrence include reinfection from untreated sexual partners, survival of residual pathogens, failure to re-establish protective vaginal flora, or persistent host susceptibility factors.[8,9] This recurrence has significant negative impacts on women’s physical, psychological, sexual, and social wellbeing, including lowered self-esteem and avoidance of sexual activity.[10] Research indicates that some strains of G. vaginalis are resistant to metronidazole and clindamycin, resulting in treatment failures. The formation of biofilms by bacteria linked to BV further reduces antibiotic effectiveness. These findings highlight the need for new strategies to target biofilms and antibiotic-resistant bacteria.[11,12] Recent research has focused on host-mediated factors, particularly vaginal pH modulation, as a strategy to prevent recurrence. Interventions such as local lactobacilli supplementation, lactic acid, hydrogen peroxide, and acetic acid have been explored.[13] Another approach involves vaginal vitamin C (ascorbic acid), formulated for sustained release to maintain an acidic environment and promote flora restoration.[14,15] Vitamin C, a readily available and affordable water-soluble antioxidant, mitigates oxidative damage by scavenging physiological reactive oxygen species such as hydroxyl, superoxide, and peroxyl radicals. Cellular uptake of vitamin C is crucial for its function.[16] In the vagina, vitamin C increases acidity by lowering pH, thereby creating an unfavorable environment for bacteria associated with BV. This action inhibits pathogens like G. vaginalis and Prevotella species, which thrive at higher pH levels, and also compensates for the diminished hydrogen peroxide production often observed in BV due to reduced lactobacilli. Consequently, it aids in restoring the vaginal ecosystem.[17] While some randomized controlled trials (RCTs) suggest vitamin C’s efficacy may be comparable to standard therapies, others report limited effectiveness.[14,15,18] For instance, one study found that long-term use of vaginal ascorbic acid improved abnormal vaginal microflora, especially in pregnant women, yet it showed no significant improvement in aerobic vaginitis or BV cases.[19]

Given the mixed results and the absence of a comprehensive synthesis of existing evidence, there is a critical need for a meta-analysis to systematically evaluate the effectiveness of vitamin C in treating and preventing BV. Such systematic evaluation would ascertain vitamin C’s effectiveness in both treating and preventing BV, delineate its therapeutic magnitude, compare its utility against established antibiotic regimens, and pinpoint deficiencies in current knowledge concerning optimal dosage, treatment duration, and specific patient cohorts. Addressing these informational lacunae is paramount for refining clinical guidelines and optimizing BV management, thereby decreasing recurrence rates and fostering improved reproductive health outcomes for women.

Study objectives

This study seeks to evaluate the efficacy of vitamin C supplementation in the management of BV, with a particular focus on its influence on vaginal pH, the presence of clue cells, vaginal discharge characteristics, and the Whiff test result.

Materials and Methods

This study adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to ensure rigorous methodology and transparent reporting.[20]

Data sources and strategy

A comprehensive literature search was conducted across multiple databases, including MEDLINE (via PubMed), Scopus, Web of Science, and Iranian databases, as well as gray literature sources, with no time restrictions up to October 29, 2024. The strategy incorporated both MeSH terms and free-text keywords pertinent to “Vaginosis, Bacterial”, “Bacterial Vaginosis Prophylaxis”, “Gardnerella vaginalis”, “Amsel”, “Nonspecific Vaginitis”, “Ascorbic Acid”, “Silicon-Coated Vit”, “L Ascorbic Acid”, “Vitamin C”, “Silicon-Coated Vitamin”, “Ferrous Ascorbate”, “Magnesium Ascorbate”, “Magnesium Ascorbicum”, “Magnesium di L Ascorbate”, “Magnorbin”, “Hybrin”, “Sodium Ascorbate”, “Ascorbic Acid, Monosodium Salt”, and “Ascorbic Acid Potassium Salt” [Supplementary File 1]. No restrictions were applied regarding language or publication date during the search.

Selecting the studies

After eliminating duplicate records, titles, and abstracts from the database, the results were screened. This was followed by a thorough examination of the full texts of potentially relevant abstracts to ensure they met the established inclusion and exclusion criteria. Both the screening and full-text reviews were conducted separately in duplicate by two independent researchers (PE, SM) and finalized through a consensus among all authors.

Inclusion criteria

• Population: Women of reproductive age who have a BV infection

• Intervention group: All forms of vitamin C

• Control group: All forms of metronidazole or a placebo

• Study design: All published RCTs

• Outcome: The outcome measure was resolution of all four diagnostic criteria for BV: (1) negative Whiff test, (2) vaginal pH <4.5, (3) normalization of vaginal discharge, and (4) reduction of clue cells to <20% of epithelial cells.

Exclusion criteria

We excluded non-RCTs, animal studies, and any investigations that failed to report these predefined clinical outcomes.

Data extraction

From each eligible study, we systematically extracted the following: study characteristics (first author, publication year), methodological details (randomization procedure, blinding approach), participant demographics and baseline characteristics, intervention protocols (including dosage and duration), control/comparator group specifications, outcome measures and assessment tools, and key reported findings.

The third researcher (MI) resolved any disagreements regarding the choice of articles and data extraction.

Quality assessment

Two independent reviewers (PE and SM) conducted methodological quality evaluations using standardized criteria. Discrepancies in quality ratings were resolved through consultation with a third senior researcher (MI).

The validated Verhagen tool was employed to systematically assess study quality across eight critical domains: Appropriate treatment allocation methodology, Baseline comparability of groups for key prognostic factors, Clear specification of eligibility criteria, Blinding of outcome assessors, Blinding of healthcare providers, Blinding of study participants, Comprehensive reporting of primary outcomes (point estimates with variability measures), and Application of intention-to-treat analysis.

Based on these criteria, studies were classified into three quality tiers: High quality: Meeting ≥6 criteria, Moderate quality: Fulfilling 4–5 criteria, and Low quality: Satisfying ≤3 criteria.[21]

Quality of evidence assessment

The Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework was utilized to assess the quality of evidence for outcomes, classifying it into four levels: ‘high,” “moderate,” “low,” and “very low.” High-quality evidence indicates that further research is very unlikely to alter confidence in the effect estimate. Moderate-quality evidence suggests that further research is likely to have an important impact. Low-quality evidence implies that further research is very likely to have an important impact, and very low-quality evidence means any effect estimate is uncertain. The assessment process began with an initial evidence rating of “high” for randomized trials. Downgrading occurred based on risk of bias (study limitations), inconsistency (I² >50% indicating substantial heterogeneity), indirectness (population, intervention, or outcome differences), imprecision (95% confidence interval [CI] crossing the null threshold [1.0 for ratios]), and publication bias. Upgrading was considered in cases of a large magnitude of effect, where all plausible biases would underestimate the effect, and a dose-response gradient was present[22] [Table 2].

Table 2.

Grading of Recommendations Assessment, Development and Evaluation evidence profile

Certainty assessment														Number of patients				Effect				Certainty		Importance
Number of studies		Study design		Risk of bias		Inconsistency		Indirectness		Imprecision		Other considerations		Vitamin C		Comparison		Relative (95% CI)		Absolute (95% CI)
Negative Whiff test
6		Randomized trials		Not serious		Seriousa		Not serious		Not serious		None		295/385 (76.6%)		231/383 (60.3%)		RR 1.19 (0.97 to 1.47)		115 more per 1000 (from 18 fewer to 283 more)		⨁⨁⨁◯ Moderatea		Critical
pH <4.5
6		Randomized trials		Not serious		Not seriousb		Not serious		Not serious		None		242/385 (62.9%)		142/383 (37.1%)		RR 1.57 (1.21 to 2.03)		211 more per 1000 (from 78 more to 382 more)		⨁⨁⨁⨁ Highb		Critical
Lack of vaginal discharge
6		Randomized trials		Not serious		Seriousa		Not serious		Not serious		Publication bias strongly suspectedc		277/385 (71.9%)		221/383 (57.7%)		RR 1.23 (0.94 to 1.60)		133 more per 1000 (from 35 fewer to 346 more)		⨁⨁◯◯ Lowa,c		Critical
Clue cells <20%
6		Randomized trials		Not serious		Seriousa		Not serious		Not serious		Publication bias strongly suspectedc		293/385 (76.1%)		197/383 (51.4%)		RR 1.34 (1.06 to 1.68)		175 more per 1000 (from 31 more to 350 more)		⨁⨁◯◯ Lowa,c		Critical

^aSignificant heterogeneity has been found between studies (defined as I² > 50% or P < 0.05). ^bAlthough heterogeneity is high, it is driven by differences in the magnitude of the effect rather than by conflicting directions of effect (i.e., effectiveness vs. ineffectiveness). Statistical significance was defined as P < 0.05. CI = Confidence interval, RR = Risk ratio

Two independent researchers (PA, SM) conducted the GRADE assessment, and any discrepancies were resolved through discussion to reach consensus.

Statistical analysis

For continuous outcome measures, the mean difference (MD) with corresponding 95% CIs was calculated. Forest plots were generated to visually synthesize effect estimates across studies, with statistical significance set at P < 0.05. Between-study heterogeneity was quantified using the I² statistic, with values ≤50% indicating moderate heterogeneity and >50% indicating substantial heterogeneity. Based on these assessments, fixed-effects models were applied when I² ≤50%, and random-effects models (DerSimonian-Laird method) were used when I² >50%. Subgroup and sensitivity analyses were also employed to explore heterogeneity when applicable. Potential publication bias was evaluated through visual inspection of funnel plot symmetry and complementary statistical tests when ≥10 studies were available. All analyses were conducted using Review Manager (RevMan) version 5.3 (Cochrane Collaboration, Oxford, UK).

Ethical considerations

Ethical research standards were rigorously maintained throughout this study. Given that the primary data sources consisted of previously published research, there was no direct involvement of human or animal subjects in our analysis. We confirmed that all included studies had secured the requisite ethical approval from their institutional review boards or ethics committees.

The review protocol was prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO) under registration number CRD42024600947, 25 October 2024.

Results

Study selection

The systematic search identified 153 potentially relevant records across all databases. Following duplicate removal, 77 unique studies underwent initial screening. Title and abstract screening led to the exclusion of 34 studies that did not meet the eligibility criteria. Subsequent full-text assessment of the remaining 43 articles resulted in the exclusion of 35 additional studies, primarily due to ineligible study designs, irrelevant interventions or outcomes, and insufficient data reporting. Consequently, eight studies were included in the systematic review, and six RCTs were considered for the meta-analysis [Figure 1].

Figure 1.

PRISMA 2020 flow diagram for systematic reviews

Study characteristics and risk of bias description

The characteristics of the included studies are shown in Table 1. The included studies were conducted in various countries: three in Iran,[15,18,23] two in Germany,[8,24] and one each in Iraq,[25] Russia,[17] and Egypt.[14] All eight studies employed a two-arm RCT design. Blinding varied, with seven studies being double-blind and one being triple-blind.[18] Sample sizes ranged from 48 to 277 participants. The control group received a placebo in three studies.[8,17,24] Six studies administered 250 mg vaginal vitamin C tablets,[8,15,17,23,24,25] while the vitamin C dosage was unspecified in one study.[14] One study used a combination of 250 mg vaginal vitamin C and 500 mg oral metronidazole.[18] The duration of vitamin C intake was predominantly 6 days,[8,14,15,17,18,24] with only one study[18] using a 7-day duration. Regarding quality assessment, six studies were rated as high quality,[8,14,15,17,18,24] one as moderate quality,[25] and one as low quality.[23]

Table 1.

Characteristics of the included randomized controlled trials

First author’s name, Year, Country, Reference		Study design		Participants		Intervention group		Control Group		Outcome (s)		Finding (s)		Quality Assessment
Petersen, 2004, Germany[8]		RCT		100 female patients aged 18 years or older and suffering from nonspecific vaginitis		Vitamin C vaginal tablets (250 mg) given once a day in patients suffering from nonspecific vaginitis for 6 days		Placebo		The primary end-point was the presence in the two groups of nonspecific vaginitis 1 and 2 weeks after the end of treatment, as assessed by at least 3 out of the 4 characteristic symptoms: discharge, fishy odor, vaginal pH <4:7, and presence of clue cells		In the placebo group, 35.7% of women remained infected, while in the vitamin C group, 14% of women remained infected, which was statistically significant (P=0.02)		High quality
Abbaspoor, 2010, Iran[23]		RCT		60 nonpregnant women, aged 15–24 years, confirmed diagnosis of bacterial vaginosis by Amsel’s criteria I: 30 C: 30		250 mg vitamin C tablet via vaginal route once daily for 6 days		5 g of 0.75% vaginal gel metronidazole once daily for 5 days		Improvement and recurrence of bacterial vaginosis		The rates of improvement and recurrence in the vitamin C group were 76.7% and 9.5%, respectively, and in the metronidazole group, 80% and 5%. Statistical tests showed no significant difference between the two groups (P=0.7)		Low quality
Humadi, 2010, Baghdad[25]		RCT		101 and one woman with bacterial vaginosis, their age ranges from 18 to 40 years enroll, the diagnosis is confirmed by at least 3 out of 4 of Amsel criteria which include a thin homogeneous vaginal discharge, vaginal PH of ≥4.7, a characteristic ‘’amine odour’’ release when alkali (lo% KOH) is added to a specimen of vaginal fluid, and at least 20% of epithelial cells having the appearance of clue cell in a wet mount of vaginal fluid or on gram stain I: 51 C: 50		250 mg vitamin C vaginal table at bed time for 6 days		Oral metronidazole 500 mg twice daily for 7 days		Improvement and recurrence of bacterial vaginosis		Regarding the infection with bacterial vaginosis, there is no significant difference between the two groups, 15.9% of patients were still infected with bacterial vaginosis at 1st follow-up visit in (vagi-C) treated group. Compared to 26.7% of the metronidazole group P=0.5, this was confirmed at the 2nd follow-up visit P=0.1 Regarding vaginal PH, there is significant reduction of vaginal PH in both groups at end of Treatment, P=0.0032 in Vagi-C and P=0.0001 in metronidazole-treated group		Moderate quality
Petersen, 2011, Germany[24]		RCT		277 outpatients with at least three of the following signs (white discharge that smoothly coats the vaginal walls, pH of vaginal fluid>4.5, a fishy odor of vaginal discharge before or after addition of 10% KOH and presence of clue cells on microscopic examination I: 141 C: 136		Insert one 250 mg ascorbic acid (Vitamin C, Vagi C) tablet deeply into the vagina once daily for 6 days		Placebo		The primary efficacy endpoint was the cure rate, defined as the recovery of all inclusion criteria		ITT: Treatment response was 55.3% in the vitamin C group and 25.7% in the placebo group (P<0.001) PP: Treatment response was 66.4% in the vitamin C group and 39.3% in the placebo group (P<0.001)		High quality
Krasnopolsky, 2013, Russia[17]		RCT		142 women, after having been cured from a recent episode of BV by either metronidazole or clindamycin I: 74 C: 68		250 mg Vaginal vitamin C for Six monthly cycles, starting within 24 h of the determination of “BV cure.” The patients applied one vaginal tablet once a day for 6 consecutive days per month after menses		Placebo		Evaluate the potential effect of vitamin C in the prophylaxis of BV relapses in patients who have been cured from a BV episode		The rate of BV recurrence during the first 3 months was considerably lower in the vitamin C group (6.8%) than in the placebo (14.7%) group. Considering a 6-month treatment period, the recurrence rate in the vitamin C group (16.2%) was significantly lower (P=0.024) than in the placebo group (32.4%)		High quality
El-Saied, 2016, Egypt[14]		RCT		164 women who presented to the outpatient gynecological clinic with a diagnosis of bacterial vaginosis By Amsels criteria I: 76 C: 78		Vitamin C vaginal suppository once daily at bed time for 6 days		Metronidazole 500 mg vaginal suppository once daily at bed time for 6 days		The current study was to compare the efficacy and side effects of vaginal vitamin C suppository		The post-treatment rates of positive clue cells were, however, significantly lower among women in group Vitamin C Group when compared to those of metronidazole group. The cure rate (defined as a Nugent score less than 4) was higher in women of group Vitamin C; the difference, however, did not reach statistical significance		High quality
Mohammad-Alizadeh, 2017, Iran[18]		RCT		160 women with pure BV I: 76 C: 78		500 mg of oral metronidazole tablets twice a day along with 250 mg vitamin C vaginal tablets for 7 days		500 mg of oral metronidazole tablets twice a day		Determine the efficacy of adding vitamin C vaginal to metronidazole in treatment of BV.		The cure rate, based on Amsel and Nugent criteria, was 85.9% in intervention group and 52.3% in control group on day 10±3 (OR: 5.3, 95% CI: 2.4 to 11.6) and 87.7% in intervention group and 41.9% in control group on day 30±3 (OR: 9.8, 95% CI: 4.2 to 22.4.		High quality
Sourazur, 2023, Iran[15]		RCT		48 nonpregnant women aged 15–40 years, After the diagnosis of G. vaginalis infection based on Amsel criteria and culture methods I: 24 C: 24		Intravaginal 250 mg vitamin C		250 mg metronidazole tablets		Evaluates the effect and side effects of vitamin C vaginal tablets on Amsel criteria in patients with G. vaginalis infection		Culture and Amsel criteria showed significant improvement in both groups during the first and fourth weeks of treatment. However, the intervention group that received vitamin C showed a more substantial improvement (P<0.002, P<0.001)		High quality

I=Intervention group, C=Control group, G. vaginalis=Gardnerella vaginalis, BV=Bacterial vaginosis, RCTs=Randomized controlled trials, KOH=Potassium hydroxide, OR=Odds ratio, CI=Confidence interval

Meta-analysis findings

• Effect of vitamin C compared with vaginal metronidazole: The findings of three included studies (n = 243) showed that vitamin C and vaginal metronidazole have the same effect on the Whiff test (relative risk [RR] =1, 95% CI: 0.86–1.17, P = 0.99) [Figure 2]

• Effect of vitamin C compared to placebo: The findings of the three included studies (n = 525) showed that vitamin C did not have a greater effect on the Whiff test compared to placebo, and this difference was not significant (RR = 1.43, 95% CI: 0.93–2.21, P = 0.11). Due to high heterogeneity, the random model was used (χ² = 33.36, I² = 94%, P < 0.00001). Sensitivity analysis showed that removing studies one by one did not change the results of the subgroups or the overall result. This finding indicates that the results obtained from the meta-analysis are highly stable and reliable and are not affected by the removal of any individual study [Figure 2].

• Effect of vitamin C compared to vaginal metronidazole: Three RCTs (n = 243) evaluated the effect of intravaginal vitamin C versus metronidazole on achieving vaginal pH <4.5. The pooled analysis revealed no statistically significant difference between groups (P = 0.12), with a consistent trend favoring vitamin C across all studies (MD − 0.35, 95% CI [−0.78 to 0.08]). Analyses showed moderate heterogeneity (I² =48%). While the primary outcome did not reach statistical significance, the consistent directional effect across studies suggests vitamin C may have comparable acidification potential to standard metronidazole therapy [Figure 3].

• Effect of vitamin C compared to placebo: Due to high heterogeneity, a random model was used (χ² = 6.78, I² = 70%, P = 0.03). The findings of the three included studies (n = 525) showed that vitamin C had a greater effect on pH <4.5 compared to placebo, and this difference was significant (RR = 1.83, 95% CI: 1.36–2.48, P < 0.0001). Sensitivity analysis showed that removing studies one by one did not change the results of the subgroups or the overall outcome. This observation suggests that the meta-analysis results are highly stable and reliable as their integrity is maintained even with the exclusion of any individual study [Figure 3].

• Effect of vitamin C versus vaginal metronidazole: Due to high heterogeneity, the random model was used (χ² = 2.49, I² = 20%, P = 0.29). The results of three included studies (n = 243) showed that vitamin C and vaginal metronidazole have equal on vaginal discharge, and the effect was in favor of metronidazole (RR = 0.94% CI: 0.77–1.15, P = 0.56) [Figure 4].

• Effect of vitamin C compared to placebo: Due to high heterogeneity, the random model was used (χ² = 8.61, I² = 77%, P = 0.01). The findings of three included studies (n = 525) showed that vitamin C has a greater effect on vaginal discharge compared to placebo and this difference is significant (RR = 1.47, 95% CI: 1.09–1.98, P = 0.01). Sensitivity analysis showed that the overall result did not change by removing the included studies one by one [Figure 4].

• Effect of vitamin C compared to vaginal metronidazole: Due to high heterogeneity, the random model was used (χ² = 6.13, I² = 67%, P = 0.05). The findings of three included studies (n = 243) showed that vitamin C and vaginal metronidazole have a similar positive effect on Clue cells and this difference is not significant (RR = 1.08, CI: 0.81–1.43, P = 0.61) [Figure 5].

• Effect of vitamin C compared to placebo: Due to high heterogeneity, a random model was used (χ² = 4.44, I² = 55%, P = 0.11). The findings of the three included studies (n = 525) showed that vitamin C has a greater effect on Clue cells compared to placebo, and this difference is significant (RR = 1.65, 95% CI: 1.32–2.05, P < 0.00001). The sensitivity analysis revealed that findings and overall results remained unchanged when individual studies were excluded. This observation indicates that the meta-analysis results are highly stable and reliable as their integrity is not compromised by the exclusion of any individual study. This stability in the results enhances confidence in the overall findings, indicating that the meta-analysis results are statistically robust and reliable [Figure 5].

Figure 2.

Forest plot of the impact of vaginal vitamin C on Whiff test

Figure 3.

Forest plot of the impact of vaginal vitamin C on pH <4.5

Figure 4.

Forest plot of the impact of vaginal vitamin C on vaginal discharge

Figure 5.

Forest plot of the impact of vaginal vitamin C on the clue cell <20%

Discussion

This study aimed to investigate the effectiveness of vitamin C supplementation in the treatment of BV. The findings indicate that vitamin C effectively improves vaginal pH and reduces clue cells, key indicators of BV. However, its effects on other clinical signs, such as the Whiff test and vaginal discharge, were not statistically significant.

Clue cells are a common clinical marker for diagnosing BV. The observed reduction in clue cells after vitamin C administration likely stems from its microbiological mechanisms: Ascorbic acid lowers vaginal pH, creating favorable conditions for lactobacilli colonization. By supporting lactic acid production, vitamin C helps re-establish the protective vaginal microbiota. The resulting acidic environment (pH < 4.5) then suppresses the growth of BV-associated bacteria (e.g., G. vaginalis) that contribute to clue cell formation.[9,17] Some studies suggest that vitamin C’s antioxidant properties may destabilize pathogenic biofilms by reducing oxidative stress in the vagina, supporting lactobacilli and inhibiting harmful microbes. This indicates that vitamin C could help maintain a balanced microbiome through its effects on biofilms and immune modulation.[26,27] Regular use of vitamin C vaginal tablets after antibiotic treatment reduces BV recurrence rates by maintaining vaginal acidity and controlling bacterial overgrowth until lactobacilli populations are restored.[17]

This biological plausibility is supported by in vitro studies demonstrating vitamin C’s ability to enhance lactobacilli viability while inhibiting biofilm formation by anaerobic BV pathogens.[14] The significant improvement in vaginal pH observed in the present study aligns with previous researches that emphasize the critical role of acidity in maintaining vaginal health.[18,23,25,28] A lower vaginal pH can inhibit the growth of pathogenic anaerobic bacteria associated with BV, thus leading to symptom relief and restoration of a healthy vaginal environment.[17,29]

Abbaspoor et al. reported that only 40% of patients achieved a vaginal pH below 4.5 one week after vitamin C vaginal tablet administration.[15] Similarly, another study evaluating vaginal ascorbic acid’s impact on abnormal vaginal microflora found that vitamin C improved both vaginal pH and microflora, particularly in pregnant women.[19] However, the effectiveness of acidification in improving BV syndrome has been inconsistent across clinical trials.[30] The varying effectiveness of different acid agents likely depends on their rates of absorption, metabolism, adhesion to the vaginal mucosa, and clearance via vaginal secretions.[31]

The Whiff test, which detects a fishy odor in vaginal discharge after adding potassium hydroxide (KOH), has moderate reliability, but various factors can influence its results. These include the potency of the KOH solution, timing, sample size, and the observer’s skill, all of which can affect consistency and statistical significance.[32] Relying solely on symptoms or even the Whiff test can lead to missed diagnoses of vaginal infections due to false negatives or inconsistent test results, potentially reducing statistical power compared to methods like vaginal pH measurement.[33]

Regarding the prophylaxis of BV, a promising approach involves the prolonged use of 250 mg of vitamin C for 6 consecutive days each month, starting after menstruation. This method appears to reduce the recurrence of BV episodes, particularly when maintained for at least 6 months. The only study that specifically explored vitamin C as a prophylactic measure for BV was conducted by Krasnopolsky et al.[17] Therefore, more research is needed to support these findings. Additionally, it would be valuable to compare the efficacy of vitamin C with other preventive methods, such as probiotics.

The certainty of evidence varied across outcomes in this meta-analysis. High confidence was found for vitamin C’s effect on normalizing vaginal pH, with consistent benefits despite variations in effect size. Moderate confidence was assigned to the negative Whiff test outcome due to interstudy variability. Conversely, the evidence for reducing clue cells and resolving vaginal discharge was of low certainty, attributed to inconsistent results and potential publication bias, warranting cautious interpretation.

It is important to note the unreported comorbidities in many studies, such as sexually transmitted infections or other gynecological diseases, which may affect treatment responses. Furthermore, the unknown marital status and sexual activity of participants could have influenced their risk factors for BV and the interventions’ effectiveness.

Strengths and limitations

Key strengths of this study include a comprehensive literature search across multiple databases, ensuring a diverse range of relevant studies. The exclusive inclusion of (RCTs enhances the quality of evidence by minimizing bias and confounding variables. However, the study also has limitations. The inclusion of research with varying quality may introduce biases and affect the reliability of the overall results. Furthermore, significant variations in sample sizes across studies raise concerns about potential underpowering to detect subtle but clinically relevant effects. Although the meta-analysis comprised 1052 participants, individual studies may lack adequate representation or statistical power. Future large-scale RCTs with standardized protocols for vitamin C administration (dosage, form, and duration) are needed to clarify its efficacy in treating BV. These studies should balance generalizability with the nuances of treatment effects. Additionally, long-term studies examining the impact of vitamin C on BV recurrence will be valuable for assessing its overall effectiveness.

Conclusion

This systematic review provided promising evidence for the use of vitamin C as an adjunctive therapy for BV. While the observed improvements in pH levels and reductions in clue cells are encouraging, further research is necessary to confirm these findings, address existing limitations, and optimize treatment protocols. This line of investigation could significantly contribute to the development of nonantibiotic approaches for managing BV.

Conflicts of interest

There are no conflicts of interest.

Supplementary File 1

Vitamin C AND BV 29/10/2024

“Vaginosis, Bacterial” OR “Bacterial Vaginosis” OR “Bacterial Vaginosis Prophylaxis” OR “Gardnerella vaginalis” OR Amsel OR “Bacterial Vaginitis” OR “Bacterial Vaginitides” OR “Nonspecific Vaginitis” OR “Bacterial Vaginoses”

“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”

Pubmed: 19

(("Vaginosis, Bacterial"[Title/Abstract] OR "Bacterial Vaginosis"[Title/Abstract] OR "Bacterial Vaginosis Prophylaxis"[Title/Abstract] OR "Gardnerella vaginalis"[Title/Abstract] OR Amsel[Title/Abstract] OR "Bacterial Vaginitis"[Title/Abstract] OR "Bacterial Vaginitides"[Title/Abstract] OR "Nonspecific Vaginitis"[Title/Abstract] OR "Bacterial Vaginoses"[Title/Abstract]) OR ("Vaginosis, Bacterial" OR "Bacterial Vaginosis" OR "Bacterial Vaginosis Prophylaxis" OR "Gardnerella vaginalis" OR Amsel OR "Bacterial Vaginitis" OR "Bacterial Vaginitides" OR "Nonspecific Vaginitis" OR "Bacterial Vaginoses"[MeSH Terms])) AND (("Ascorbic Acid"[Title/Abstract] OR "Silicon-Coated Vit"[Title/Abstract] OR "L Ascorbic Acid"[Title/Abstract] OR "Vitamin C"[Title/Abstract] OR "Silicon-Coated Vitamin"[Title/Abstract] OR "Ferrous Ascorbate"[Title/Abstract] OR "Magnesium Ascorbate"[Title/Abstract] OR "Magnesium Ascorbicum"[Title/Abstract] OR "Magnesium di L Ascorbate"[Title/Abstract] OR Magnorbin[Title/Abstract] OR Hybrin[Title/Abstract] OR "Sodium Ascorbate"[Title/Abstract] OR "Ascorbic Acid, Monosodium Salt"[Title/Abstract] OR "Ascorbic Acid Potassium Salt"[Title/Abstract]) OR ("Ascorbic Acid" OR "Silicon-Coated Vit" OR "L Ascorbic Acid" OR "Vitamin C" OR "Silicon-Coated Vitamin" OR "Ferrous Ascorbate" OR "Magnesium Ascorbate" OR "Magnesium Ascorbicum" OR "Magnesium di L Ascorbate" OR Magnorbin OR Hybrin OR "Sodium Ascorbate" OR "Ascorbic Acid, Monosodium Salt" OR "Ascorbic Acid Potassium Salt"[MeSH Terms]))

Cochrane: 17

#1 (“Vaginosis, Bacterial” OR “Bacterial Vaginosis” OR “Bacterial Vaginosis Prophylaxis” OR “Gardnerella vaginalis” OR Amsel OR “Bacterial Vaginitis” OR “Bacterial Vaginitides” OR “Nonspecific Vaginitis” OR “Bacterial Vaginoses”):ti,ab,kw

#2 MeSH descriptor: [Vaginosis, Bacterial] explode all trees

#3 #1 OR #2

#4 (“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”):ti,ab,kw

#5 MeSH descriptor: [Ascorbic Acid] explode all trees

#6 #4 OR #5

#7 #3 AND #6

Embase: 49

#1 'vaginosis, bacterial':ti,ab,kw OR 'bacterial vaginosis':ti,ab,kw OR 'bacterial vaginosis prophylaxis':ti,ab,kw OR 'gardnerella vaginalis':ti,ab,kw OR amsel:ti,ab,kw OR 'bacterial vaginitis':ti,ab,kw OR 'bacterial vaginitides':ti,ab,kw OR 'nonspecific vaginitis':ti,ab,kw OR 'bacterial vaginoses':ti,ab,kw OR 'vaginosis, bacterial'/exp OR 'bacterial vaginosis'/exp OR 'bacterial vaginosis prophylaxis' OR 'gardnerella vaginalis'/exp OR amsel OR 'bacterial vaginitis'/exp OR 'bacterial vaginitides' OR 'nonspecific vaginitis'/exp OR 'bacterial vaginoses'

#2 'ascorbic acid':ti,ab,kw OR 'silicon-coated vit':ti,ab,kw OR 'l ascorbic acid':ti,ab,kw OR 'vitamin c':ti,ab,kw OR 'silicon-coated vitamin':ti,ab,kw OR 'ferrous ascorbate':ti,ab,kw OR 'magnesium ascorbate':ti,ab,kw OR 'magnesium ascorbicum':ti,ab,kw OR 'magnesium di l ascorbate':ti,ab,kw OR magnorbin:ti,ab,kw OR hybrin:ti,ab,kw OR 'sodium ascorbate':ti,ab,kw OR 'ascorbic acid, monosodium salt':ti,ab,kw OR 'ascorbic acid potassium salt':ti,ab,kw OR 'ascorbic acid'/exp OR 'silicon-coated vit' OR 'l ascorbic acid'/exp OR 'vitamin c'/exp OR 'silicon-coated vitamin' OR 'ferrous ascorbate'/exp OR 'magnesium ascorbate'/exp OR 'magnesium ascorbicum' OR 'magnesium di l ascorbate' OR 'magnorbin'/exp OR 'hybrin'/exp OR 'sodium ascorbate'/exp OR 'ascorbic acid, monosodium salt' OR 'ascorbic acid potassium salt'/exp

#3 #1 AND #2

Scopus: 43

(TITLE-ABS-KEY("Vaginosis, Bacterial" OR "Bacterial Vaginosis" OR "Bacterial Vaginosis Prophylaxis" OR "Gardnerella vaginalis" OR Amsel OR "Bacterial Vaginitis" OR "Bacterial Vaginitides" OR "Nonspecific Vaginitis" OR "Bacterial Vaginoses") AND TITLE-ABS-KEY("Ascorbic Acid" OR "Silicon-Coated Vit" OR "L Ascorbic Acid" OR "Vitamin C" OR "Silicon-Coated Vitamin" OR "Ferrous Ascorbate" OR "Magnesium Ascorbate" OR "Magnesium Ascorbicum" OR "Magnesium di L Ascorbate" OR Magnorbin OR Hybrin OR "Sodium Ascorbate" OR "Ascorbic Acid, Monosodium Salt" OR "Ascorbic Acid Potassium Salt"))

ISI: 20

https://www.webofscience.com/wos/woscc/summary/41ac3886-22af-4fac-877f-8e08ec65b071-011aa2c82e/relevance/1

#1 (((TI=(“Vaginosis, Bacterial” OR “Bacterial Vaginosis” OR “Bacterial Vaginosis Prophylaxis” OR “Gardnerella vaginalis” OR Amsel OR “Bacterial Vaginitis” OR “Bacterial Vaginitides” OR “Nonspecific Vaginitis” OR “Bacterial Vaginoses”)) OR AB=(“Vaginosis, Bacterial” OR “Bacterial Vaginosis” OR “Bacterial Vaginosis Prophylaxis” OR “Gardnerella vaginalis” OR Amsel OR “Bacterial Vaginitis” OR “Bacterial Vaginitides” OR “Nonspecific Vaginitis” OR “Bacterial Vaginoses”)) OR AK=(“Vaginosis, Bacterial” OR “Bacterial Vaginosis” OR “Bacterial Vaginosis Prophylaxis” OR “Gardnerella vaginalis” OR Amsel OR “Bacterial Vaginitis” OR “Bacterial Vaginitides” OR “Nonspecific Vaginitis” OR “Bacterial Vaginoses”)) OR KP=(“Vaginosis, Bacterial” OR “Bacterial Vaginosis” OR “Bacterial Vaginosis Prophylaxis” OR “Gardnerella vaginalis” OR Amsel OR “Bacterial Vaginitis” OR “Bacterial Vaginitides” OR “Nonspecific Vaginitis” OR “Bacterial Vaginoses”)

#2 ((((TI=(“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”)) OR AB=(“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”)) OR AK=(“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”)) OR AK=(“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”)) OR KP=(“Ascorbic Acid” OR “Silicon-Coated Vit” OR “L Ascorbic Acid” OR “Vitamin C” OR “Silicon-Coated Vitamin” OR “Ferrous Ascorbate” OR “Magnesium Ascorbate” OR “Magnesium Ascorbicum” OR “Magnesium di L Ascorbate” OR Magnorbin OR Hybrin OR “Sodium Ascorbate” OR “Ascorbic Acid, Monosodium Salt” OR “Ascorbic Acid Potassium Salt”)

#3 #2 AND #1

Funding Statement

Nil.