NEC is a prevalent gastrointestinal diseases in neonates, characterized by high morbidity and mortality rates. Its onset is often insidious, progression rapid, and prevention challenging [52]. The younger the gestational age and the lower the birth weight, the poorer the intestinal mucosal barrier function and the lower the abundance of intestinal flora, resulting in greater susceptibility to NEC and a higher probability of developing severe disease [53].

A 2020 retrospective study conducted in a tertiary NICU at Norfolk and Norwich University Hospital in the UK found that routine administration of Lactobacillus acidophilus and Bifidobacterium spp. significantly reduced the incidence of NEC in extremely preterm infants, with no reported cases of probiotic sepsis [1]. A 2022 double-blind RCT at Tygerberg Hospital, South Africa, reported a significantly lower incidence of NEC in preterm infants receiving Bifidobacterium bifidum and Lactobacillus acidophilus compared to the placebo group. The study concluded that the use of probiotics to prevent NEC is a safe and effective measure [2]. A 2023 retrospective study in Australia also supported the use of Bifidobacterium combined with Lacticaseibacillus rhamnosus as a preventive strategy for NEC [3]. Consistently, a network meta-analysis by Beghetti et al. (2021) [54] confirmed that Bifidobacterium lactis Bb-12/B94 reduces the risk of stage $\ge$2 NEC in preterm infants, with greater benefits observed in exclusively human milk–fed infants.

Morgan et al. (2020) [55] analyzed 63 trials including 15,712 preterm infants and concluded that combinations of Lactobacillus and Bifidobacterium, or Lactobacillus reuteri and Lacticaseibacillus rhamnosus, effectively reduced severe NEC and mortality. However, combinations involving Bacillus and Enterococcus were less effective. Chi et al. (2021) [56] reviewed 45 RCTs involving 12,320 preterm infants and found that the combined use of Lactobacillus and Bifidobacterium, or Lactobacillus plus prebiotics, was more effective than single-strain probiotics. Wang et al. (2023) [57] identified multi-strain probiotics alone or combined with oligosaccharides as among the most effective interventions for reducing NEC. In contrast, a 2024 retrospective study from the Czech Republic by Korček and Straňák [4] found no statistically significant difference in NEC incidence or mortality between single-strain and multi-strain probiotics, potentially due to a small sample size or low baseline NEC incidence.

In 2022, Samara et al. [5] (Canada) investigated preterm infants under 29 weeks gestation using a multi-strain probiotic mixture consisting of Bifidobacterium breve HA129, Bifidobacterium bifidum HA132, Bifidobacterium longum subsp. infantis HA116, Bifidobacterium longum HA135, and Lacticaseibacillus rhamnosus HA111. The intervention accelerated intestinal microbiota maturation toward a term-like profile and reduced intestinal pro-inflammatory markers associated with NEC. While not directly demonstrating reduced NEC morbidity or mortality, the study provided mechanistic support for bifidobacteria’s potential benefit in extremely preterm infants (28 weeks). By contrast, a large RCT in the United Kingdom (Costeloe et al. [6]) evaluating Bifidobacterium breve BBG-001 in preterm infants (23–30 weeks) found no significant effect on NEC incidence or mortality.

At present, current clinical evidence suggests that probiotics can reduce the incidence of NEC and lower NEC-related mortality, with Lactobacillus spp. (e.g., L. rhamnosus, L. reuteri, L. acidophilus) and Bifidobacterium spp. (e.g., B. longum, B. breve, B. animalis) being the most commonly recommended. Administration typically begins once a minimum enteral feeding volume is achieved (e.g., 60–80 mL/kg/day) and continues until 34–36 weeks postmenstrual age (PMA) or discharge, with most regimens delivering approximately 10⁹ CFU/day.

Multicenter and long-term real-world data support the feasibility and potential benefits of probiotic supplementation; however, limitations remain, including substantial heterogeneity in strains, dosage, initiation thresholds, and duration of treatment; insufficient statistical power due to low baseline NEC incidence and restricted external validity between large negative single-strain RCTs and small positive or mechanistic trials. Future research should focus on standardized, adequately powered, head-to-head randomized controlled trials of specific strains in extremely preterm and very low birth weight populations.

A 2022 double-blind, placebo-controlled randomized clinical trial by Sowden et al. [2] found that combined use of Lactobacillus acidophilus and Bifidobacterium significantly reduced the incidence of FI. The probiotic group also achieved full enteral feeding sooner and regained birth weight earlier than the placebo group [7]. In studies conducted by Indrio and colleagues [8, 9] in Italy, preterm infants with mean gestational ages of approximately 30 weeks and 34 weeks. Supplementation at 10⁸ CFU/day for one month effectively reduced FI occurrence and shortened the time to full enteral nutrition. A meta-analysis of nine studies involving 1244 preterm infants with FI concluded that probiotics promote early growth and reduce FI incidence, although it did not identify preferred specific strains [58]. Similarly, a recent systematic review and meta-analysis in extremely preterm infants reported a non-significant but consistent trend toward improved feeding tolerance with probiotic supplementation, reflected by shorter time to full enteral feeding and reduced reliance on parenteral nutrition [59].

Neonates have a relatively weak immune barrier, making them prone to infections. Common neonatal infections include pneumonia, necrotizing enterocolitis, and sepsis. Antibiotics are often used to treat these conditions. However, prolonged antibiotic use can significantly disrupt the composition and function of the gut microbiota, and this antibiotic-associated dysbiosis may persist even after therapy concludes [60]. Probiotics may prevent AAD through multiple mechanisms, including modulating intestinal microbiota, increasing short-chain fatty acid production, regulating bile acid metabolism, and enhancing gut barrier function and immune responses [61].

Between 2008 and 2011, Wu et al. [10] administered Lactobacillus bifidus triplex tablets to neonates with purulent meningitis during antibiotic treatment, and the study demonstrated a significant reduction in the incidence of AAD and a delay in its onset. In 2013, Liu et al. [11] reported that children on long-term antibiotic therapy who received Bacillus subtilis bifidus granules had a significantly lower incidence of AAD (2%) compared to the control group (36%). Collectively, these studies indicate that probiotic intervention can delay or even prevent the occurrence of AAD. Several studies further suggest that probiotics can aid in the treatment of neonatal AAD. They can alleviate symptom severity (e.g., diarrhea, abdominal pain) and shorten the duration of AAD. A randomized controlled trial in 2021 confirmed that Clostridium butyricum and Bifidobacterium infantis live powder can alleviate clinical symptoms of antibiotic-associated diarrhea, such as abdominal pain and diarrhea [12]. Feng Aimin and others investigated the therapeutic effects of a bivalent probiotic (Clostridium butyricum and Bifidobacterium infantis) versus Saccharomyces boulardii for AAD. The bivalent probiotic showed superior outcomes regarding time to diarrhea cessation, hospitalization duration, and the overall therapeutic efficacy [13]. This conclusion is corroborated by the findings of a clinical study carried out by Du and Wang in 2020 [14]. The superior efficacy of the bivalent preparation may be attributable to its combination of multiple bacterial strains, which more closely mimics the normal proportion of intestinal flora in the human body.

A 2017 multi-center randomized controlled trial in China showed that administration of Saccharomyces boulardii alongside antibiotics significantly reduced the incidence of diarrhea in children receiving one or more antibiotics for $\ge$5 days, with a reduction of over 60%. Moreover, within 14 days after antibiotic cessation, the intervention group’s risk of diarrhea remained more than 80% lower than that of the control group [15]. In 2024, a prospective study by Zhang et al. [16] in China found that both Saccharomyces boulardii and Bifidobacterium effectively improved intestinal health and prevented AAD in infants and young children, with no significant difference between them. The study also found no significant difference in fecal coccobacilli counts at 14 and 21 days after Bifidobacterium administration, suggesting maximal microbiota modulation was achieved by day 14, with prolonged supplementation offering no additional benefit. A 2019 systematic review by Guo et al. [62], covering children aged 3 days to 18 years, indicated that Lacticaseibacillus rhamnosus and Saccharomyces boulardii were the most promising probiotics for AAD prevention, with daily doses $>$5 $\times$ 10⁹ CFU showing superior efficacy. Notably, these studies included children across a broad age range (3 days to 18 years) and were not tailored specifically to neonates. Nonetheless, they offer valuable insights for strain selection, dosage, and intervention duration in neonatal AAD. In contrast, an RCT by Lukasik et al. [17] involving children aged 3 months to 18 years found that Bifidobacterium and Lactobacillus acidophilus decreased the risk of diarrhea during and up to 7 days after antibiotic therapy, but did not specifically reduce the risk of AAD, highlighting how variations in the definition of AAD can influence clinical trial outcomes and their interpretation.

In summary, substantial evidence confirms the efficacy of probiotics in both preventing and treating AAD. Saccharomyces boulardii and Lacticaseibacillus rhamnosus have the strongest evidence base, while Clostridium butyricum and Bifidobacterium longum may also provide benefits in children. Early administration of probiotics alongside antibiotics is recommended to minimize disruption of the gut microbiota and mucosal barrier. However, the optimal duration of probiotic therapy requires further clinical investigation.

A substantial body of randomised controlled trials shows that probiotics help prevent disease and serve as adjuncts to therapy across diverse gastrointestinal conditions. Recent experimental and translational work has clarified the biological underpinnings of these effects, pointing to mechanisms that span the intestinal barrier, immune modulation, and metabolic support.

Probiotics reshape the gut microbiota by encouraging the colonisation and expansion of beneficial taxa such as Bifidobacterium and Lactobacillus, while curbing the overgrowth of potential pathogens to preserve microbial homeostasis. A healthier community structure limits pathogen adhesion and translocation, thereby reducing the likelihood of intestinal barrier injury. In addition to these microbiota-mediated actions, certain strains directly upregulate tight junction proteins in intestinal epithelial cells—including occludin, claudin, and ZO-1. By reinforcing intercellular integrity, probiotics help normalise mucosal permeability and support the recovery of barrier function [63, 64].

Probiotics shape host immunity by remodelling the microbial community and by directly engaging receptors on epithelial and immune cells, including TLR2, TLR4, and TLR9. Through these interactions they tune key signalling pathways—most notably NF-$\kappa$B and MAPK. A substantial body of evidence shows that probiotics downregulate pro-inflammatory cytokines (TNF-$\alpha$, IL-1$\beta$, IL-6) and upregulate anti-inflammatory mediators (IL-10, TGF-$\beta$), thereby tempering excessive inflammation and sustaining immune homeostasis [65]. These effects are clinically relevant: they limit intestinal mucosal injury, foster immune tolerance, and improve feeding tolerance.

Probiotic-derived short-chain fatty acids—acetate, propionate, and butyrate—serve as the main fuel for colonocytes. Beyond energising the epithelium, SCFAs stimulate epithelial proliferation and repair, trigger mucus secretion from goblet cells, bolster antimicrobial peptide production, and preserve an acidic luminal milieu that suppresses pathogenic growth [66]. Collectively, this metabolic support is pivotal during intestinal inflammation and tissue repair, accelerating the recovery of mucosal structure and function.

Probiotics operate along intersecting pathways: they fortify the intestinal epithelial barrier; directly calibrate signalling to dampen inflammation; and harness microbial metabolites to optimise the intestinal milieu and drive epithelial repair. Taken together, these actions offer a strong biological rationale for the clinical benefits reported in NEC, FI, and AAD.

In neonatal hyperbilirubinaemia, emerging work shows a layered mode of action: beyond reshaping the gut environment, probiotics tune metabolic and signalling checkpoints that, in turn, influence bilirubin production, conversion, and clearance. These convergent effects help explain their growing therapeutic promise.

In early neonatal life the gut microbiota is immature: aerobes predominate, while obligate anaerobes such as Bifidobacterium and Lactobacillus are relatively scarce [80]. This imbalance drives the accumulation of harmful metabolites, facilitating both the production and uptake of bilirubin. Probiotic supplementation accelerates the colonisation and expansion of beneficial taxa and curbs the growth of potential pathogens (e.g., Enterobacteriaceae and Enterococcus), thereby restoring microbial homeostasis. As the community adopts a healthier profile, bilirubin output falls and the intestinal environment stabilises—setting the stage for the spontaneous clearance of jaundice.

Probiotics also blunt the enterohepatic circulation. In the neonatal gut, $\beta$-glucuronidase hydrolyses conjugated bilirubin to its unconjugated form, which is readily reabsorbed and sustains hyperbilirubinaemia [81]. By producing acid, probiotics lower the luminal pH, suppressing enzyme-producing bacteria and directly diminishing enzymatic activity; the result is less hydrolysis of conjugated bilirubin. An acidified intestinal milieu further promotes anaerobe growth, yielding a more stable ecosystem that disfavors bilirubin reabsorption.

Probiotics also meaningfully influence gut motility. By generating SCFAs, they trigger contractions of the intestinal smooth muscle, sharpen gastrointestinal peristalsis, and ease the excretion of bilirubin with the faeces [82]. As the lumen becomes more acidic and its osmotic pressure rises, water secretion increases and stools are diluted, which further hastens transit. Evidence from several studies indicates that multi-strain formulations containing Bifidobacterium and Lactobacillus acidophilus act synergistically to boost motility and support bilirubin metabolism, resulting in a marked reduction in the duration of jaundice.

Overall, probiotics operate along a continuum: they restore microbial balance, suppress $\beta$-glucuronidase activity, interrupt the enterohepatic recycling of bilirubin, and enhance motility and elimination—shifting the system from “less production” to “less reabsorption” to “more excretion”. This coherent biological orchestration positions probiotics as a valuable adjunct to phototherapy in neonatal jaundice and offers a credible, evidence-informed pathway for non-pharmacological intervention.

VAP is defined as infectious inflammation of the lung parenchyma occurring $\ge$48 hours after the initiation and up to 48 hours after discontinuation of mechanical ventilation. In recent years, advances in perinatal medicine have led to the survival of increasingly premature infants, increased mechanical ventilation use, and a rising VAP incidence. Once VAP occurs in infants, treatment becomes more challenging, hospital stay is prolonged, and in severe cases it can be life-threatening.

Only a limited number of studies have reported the use of probiotics in VAP. In the neonatal intensive care unit (NICU) population, a randomized controlled trial enrolling full-term infants (gestational age 37–42 weeks) requiring invasive mechanical ventilation showed that daily supplementation with a probiotic preparation containing 2 $\times$ 10⁹ CFU of Bifidobacterium animalis subsp. lactis BB-12 was associated with a significantly lower incidence of VAP, as well as shorter duration of mechanical ventilation and NICU stay. It has been proposed that probiotics may reduce the risk of respiratory pathogen colonization and pulmonary infection by enhancing mucosal barrier function, inhibiting pathogen adhesion and translocation, and modulating innate and adaptive immune responses [35].

Clinical studies on probiotics for VAP prevention remain limited in number, with those focusing on neonatal VAP being exceedingly scarce. Notably, an international RCT involving children under 12 years of age demonstrated that prophylactic administration of probiotics (Lactobacillus and Bifidobacterium at 3 $\times$ 10⁹ CFU/day, administered for 7 days or until discharge) reduced the incidence of VAP in Pediatric Intensive Care Unit (PICU) patients [36]. This finding provides valuable reference for future neonatal VAP trials, and it awaits further studies to confirm effectiveness and clarify mechanisms.

A randomized, double-blind, placebo-controlled trial in Finland (2000–2003) gave full-term newborns a 6-month intervention with multi-strain probiotics including Lacticaseibacillus rhamnosus GG and LC705, Bifidobacterium lactis Bb99, and propionibacterium freudenreichii subsp. shermanii JS. During the intervention period, no adverse reactions were observed in the trial group, and the probiotic group had a lower frequency of respiratory infections [37]. A prospective clinical study in Ukraine in 2011 used Escherichia coli Nissle 1917 to supplement late preterm infants. The study found that within 28 days after birth, the proportion of acute respiratory infections (ARI) in the trial group was significantly lower than in the control group (10.0% vs 43.7%, p = 0.008) [38]. A multi-center RCT in France found that Lactobacillus fermentum had a similar effect [39]. However, an RCT in Japan using Lactobacillus fermentum for late preterm infants (gestational age 37 weeks) yielded negative results [40].

BPD, a common complication in preterm infants, remains incompletely understood in its pathogenesis. Traditionally, BPD has been associated with factors such as immature lung development, hyperoxic exposure, and inflammatory responses. Recent studies, however, emphasize a close association with intestinal microbiota via the gut-lung axis. Intestinal dysbiosis may promote BPD progression, suggesting that probiotics could potentially prevent or treat BPD through this axis [83].

A retrospective clinical study in China in 2021 found that Clostridium butyricum helped reduce the risk of BPD in extremely preterm infants (gestational age $\le$32 weeks) [41]. A clinical randomized controlled trial by Li et al. [42] in 2024 also reached similar conclusions: Clostridium butyricum helped reduce the incidence of BPD in extremely preterm infants, and also shortened the oxygen administration time and hospital stay of infants.

Evidence for the use of probiotics in respiratory diseases remains limited, and the optimal timing, dosage, and duration of intervention are not well defined. Studies on VAP, ARI, and BPD are generally small-scale and heterogeneous, making it difficult to draw firm conclusions. Notably, some reports have suggested that administration of bifidobacteria within 24 hours of initiating mechanical ventilation, continued for approximately one week, may reduce both respiratory and gastrointestinal bacterial colonization in ventilated infants [43, 44]. However, this observation is based on a small number of studies and requires confirmation through well-designed, adequately powered randomized controlled trials. At present, the optimal timing for probiotic intervention in respiratory disease is currently uncertain, and further methodologically robust clinical research is needed to establish evidence-based recommendations.

As eczema peaks in infancy and early childhood rather than the neonatal period, research on probiotics for preventing and treating neonatal eczema is scarce. However, given that probiotics can exert positive effects during infancy and adolescence, early probiotic intervention in the neonatal period may reduce the subsequent development and progression of allergic diseases in infants and children.

Sun et al.’s 2021 meta-analysis [84] demonstrated that combinations of Lactobacillus and Bifidobacterium strains significantly reduced eczema incidence in children under three years of age. Notably, probiotic administration initiated early during pregnancy exhibited greater efficacy.

A 2025 RCT by Puisto et al. [45] reported similar findings: perinatal maternal probiotic intervention with Lactobacillus rhamnosus, Lactobacillus paracasei, and Bifidobacterium bifidum reduced the risk of atopic eczema in infants within the first 2 years of life. Notably, this protective effect appeared independent of gut microbiota modulation, as no statistically significant differences in gut microbial composition were detected between the groups. Additionally, a meta-analysis demonstrated that Lactobacillus rhamnosus effectively reduced eczema incidence. In the included studies, the timing of interventions ranged from 2–4 weeks prior to delivery to 6 months–2 years postpartum. The analysis revealed that this benefit was most pronounced during follow-up periods of up to 2 years and 6–7 years. By contrast, no statistically significant reduction in the incidence of atopic eczema was observed at 4–5 years or 10–11 years of follow-up [85].

CMPA is the most prevalent food allergy in neonates, characteristically manifesting with clinical features such as cutaneous eczema, respiratory symptoms, and gastrointestinal disturbances. However, due to the immature immune response and other unique physiological characteristics of neonates, the clinical manifestations of CMPA often lack specificity, frequently leading to misdiagnosis as conditions like neonatal necrotizing enterocolitis, sepsis, among others [86]. While strict avoidance of milk proteins constitutes the cornerstone of therapy, emerging evidence supports adjuvant use of probiotics to alleviate allergy-related symptoms.

Luo and Zhang’s study [46] showed that compared with the control group, after three months of continuous oral administration of probiotics (Bifidobacterium lactis BB12 + Lacticaseibacillus rhamnosus GG) in children with CMPA, significant statistical differences were observed in clinical symptoms such as vomiting, diarrhea, and food refusal, as well as in weight-for-age scores. However, no significant differences were noted during the first 1–2 months of intervention. These results indicate that probiotics should be administered for at least three months to significantly improve infant gastrointestinal function, thereby promoting nutritional metabolism and supporting weight gain in infants. Nocerino et al. [47] from Italy reported that the time to achieve immune tolerance was shortened in CMPA infants fed hydrolyzed formula supplemented with Lactobacillus rhamnosus. In addition, a six-month intervention with Bifidobacterium TMC3115 reduced allergic symptoms in CMPA infants, which is associated with an increased probiotic and decreased pathogenic bacteria proportion in the gut.

Probiotics recalibrate immune polarity by restoring the balance between Th1 and Th2 activity. Under allergic conditions, immunity is typically skewed towards a Th2 profile, with elevated IL-4, IL-5, and IL-13 driving IgE production and mast-cell degranulation. By shaping dendritic-cell differentiation and antigen presentation, probiotics enhance Th1-type signalling—most notably IFN-$\gamma$—which reins in the exaggerated Th2 response and re-establishes immune homeostasis [87, 88]. This fine-tuned redirection of the response is a central way in which probiotics mitigate allergic disease.

Probiotics engage the host immunoregulatory network, driving the differentiation and expansion of regulatory T cells (Treg) [89]. By releasing IL-10 and TGF-$\beta$, Treg dampen effector T-cell activity and quell inflammation, creating an immunosuppressive microenvironment. Evidence indicates that targeted strains—most notably Lactobacillus rhamnosus GG and Bifidobacterium longum—can raise peripheral Treg frequencies and boost their regulatory capacity, thereby softening antigen-provoked responses in allergic individuals [90].

Through complementary mechanisms, probiotics foster immune tolerance. They lower IgE concentrations, weakening immune complex–mediated allergic reactions; simultaneously they restrain overactivation of mast cells and basophils, curbing histamine release and easing symptoms at their origin [3]. Probiotic derivatives also signal via intestinal epithelial receptors to reinforce barrier function and limit antigen translocation, helping the immune system to recognise that harmless exposures need not be treated as threats.

Probiotics do more than quell inflammation: they retune the immune network’s “tone”, guiding an overresponsive system back into balance—from restoring homeostasis to fostering tolerance. This measured, long-lasting modulation gives probiotics a distinctive biological appeal in the prevention and treatment of allergic disease.

The relationship between probiotics and mineral status is complex. The systematic review by Apte et al. [91] analyzed the differences in the effects of probiotics on iron absorption between women and children. Through nalyzing 29 studies (14 in women of reproductive age, 15 in children), results for iron absorption were more favorable in women. Meta-analysis of six studies demonstrated a mean increase in serum ferritin of 2.45 ng/mL (p = 0.009) with moderate-quality evidence. More importantly, pooled data from eight studies on fractional iron absorption indicated a mean increase of 0.74% (p = 0.02), with particularly pronounced effects for galacto-oligosaccharides (GOS) and Lactiplantibacillus plantarum 299v. In contrast, the results for children were less encouraging. Meta-analysis of eight studies showed no significant change in hemoglobin, and four studies reported no improvement in serum ferritin.

The effects of probiotics on calcium and zinc nutrition also vary across populations. A randomized controlled trial by Agustina et al. [48] demonstrated that supplementation with Lactobacillus reuteri or L. casei failed to significantly improve serum calcium and zinc levels among children aged 1–6 years. However, positive results were observed in elderly [92] and postmenopausal women [93]. With regard to zinc, probiotics and zinc appear to exert a synergistic effect. In a randomized, double-blind, placebo-controlled trial involving Indonesian children aged 12–24 months, four groups received either placebo, Lactobacillus plantarum IS-10506 (10¹⁰ CFU/day), zinc (8 mg/day), or the probiotic-zinc combination for 90 days. Neither probiotic nor zinc alone significantly improved serum zinc versus baseline, whereas combined supplementation significantly increased serum zinc levels [49].

In clinical studies, randomized double-blind trials and open-label trials in children have shown that probiotic or combined prebiotic-probiotic interventions do not produce a marked improvement in vitamin A status. However, for vitamin D, an upward trend in serum levels was observed when multi-strain formulations containing Lactobacillus plantarum, L. acidophilus, Bifidobacterium infantis, and B. lactis were used [50], although statistical significance was not always clearly reported and results varied across populations. Studies in both pregnant women and children suggest that the effects depend on strain type (e.g., L. reuteri, B. animalis), dosage, and duration of intervention, and the findings remain inconsistent. Therefore, current evidence is insufficient to establish a consistent beneficial effect of probiotics on vitamin A or D status.

Evidence supporting the role of probiotics in enhancing the production of water-soluble B vitamins is relatively strong; however, this effect appears to be highly strain-specific rather than rather than a general property of a genus. Lactic acid bacteria and bifidobacteria are recognized as key contributors to B-vitamin production in the human gut, yet their synthetic capacity, the spectrum of vitamins produced, and the bioavailability of these compounds vary substantially among different strains. An animal study has shown that Bifidobacterium adolescentis can produce vitamin B9 (folate) [94]. A human study has also confirmed that Bifidobacterium adolescentis DSM 18350, B. adolescentis DSM 18352, and B. pseudocatenulatum DSM 18353 are capable of synthesizing and secreting folate in the human intestinal environment, thereby providing a constant additional source of endogenous folate within the gut lumen [95]. However, the number of high-quality randomized controlled trials is small, and direct evidence in pediatric populations, particularly in neonates, remains scarce.

Animals, plants, and fungi are incapable of vitamin B12 (cobalamin) production and it is exclusively synthesized by microorganisms. Lactobacillus reuteri CRL1098 was shown to be the first lactic acid bacteria strain able to produce a cobalamin-like compound [96]. In vitro studies have demonstrated that Lactobacillus plantarum is also capable of producing vitamin B12 [97]. In addition to direct synthesis, probiotics may improve vitamin B12 status by modulating gut microbiota composition, potentially reducing the abundance of bacterial species that degrade this vitamin [98].

Collectively, these findings indicate that while probiotics contribute significantly to B-vitamin availability, their effects are not uniform across vitamins and species. This highlights the need for precise, strain-level selection and validation in probiotic applications, particularly when targeting specific vitamins or addressing the needs of vulnerable populations such as children.