Clinical Pharmacist and Master’s student in Clinical Pharmacy with research interests in pharmacovigilance, behavioral interventions in mental health, and AI applications in clinical decision support. Experience includes digital health research with Bloomsbury Health (London) and pharmacovigilance practice in patient support programs. Published work covers drug awareness among healthcare providers, postpartum depression management, and patient safety reporting. What was reviewed?
This review article systematically examined recent research concerning the interactions between heavy and toxic metals and the gut microbiota (GM) in humans, animals, and in vitro models. The focus was on environmentally prevalent or biopersistent metals, such as arsenic, cadmium, mercury, lead, zinc, and copper, as well as several others, including nanoparticles. The review included studies published within the previous five years, identified through a structured PubMed search. It discussed how exposure to these metals through food, water, occupational, and environmental sources affects the composition, diversity, and function of the gut microbiota, and it summarized important mechanisms and outcomes. The review also highlighted the analytical methods used, such as 16S rRNA gene sequencing, metagenomics, and metabolomics, and addressed the variability in findings, which arises from differences in metal compounds, exposure modalities, durations, and baseline microbiota diversity.
Who was reviewed?
The review encompassed a wide spectrum of studies involving human populations (adults, infants, children), various animal models (rodents, fish, amphibians, birds, invertebrates such as earthworms and honey bees), and in vitro models simulating the human intestinal environment (e.g., SHIME system). Human studies included both general populations exposed to environmental factors and specific groups such as infants, pregnant women, and children with particular health conditions (e.g., autism spectrum disorder). Animal studies ranged from acute and chronic exposure scenarios to interventions with probiotics and dietary modifications. The in vitro studies mostly simulated metal exposure and transformation in the human digestive tract using human fecal microbiota. Across these diverse models, the focus was on how exposure to heavy metals and nanoparticles perturbed the gut microbiome and related metabolic and health outcomes.
Most important findings
| Key Findings | Relevance to Heavy Metal Certification Programs |
|---|---|
| Exposure to heavy metals (As, Cd, Hg, Pb, Cu, Zn, Cr, Ni, Mn, Mo, V) consistently perturbs the gut microbiota’s diversity, composition, and structure across human, animal, and in vitro studies. | Demonstrates the need to monitor and control heavy metal content in products to prevent adverse microbiota and health effects. |
| Perturbations often include a reduction in beneficial commensals (e.g., Bifidobacterium, Bacteroides) and an increase in pathogenic taxa, with changes in metabolic and inflammatory pathways. | Highlights the risk for dysbiosis, immune dysregulation, metabolic syndrome, and even disease (e.g., obesity, diabetes, cancer). |
| Specific adverse effects are dose-dependent and vary by metal, exposure route, duration, and host factors (age, sex, baseline microbiota). Essential metals like Zn and Cu are beneficial at low levels but toxic at excess, while non-essential metals (As, Cd, Pb, Hg) are harmful even at low concentrations. | Emphasizes the importance of defining safe exposure limits and considering cumulative effects of multiple metals. |
| Emphasizes the importance of defining safe exposure limits and considering the cumulative effects of multiple metals. | Suggests that emerging contaminants like metal nanoparticles also warrant rigorous assessment in certification protocols. |
| Modern analytical methods (metagenomics, metabolomics) are underutilized but provide early biomarkers of detrimental metal exposure. | Indicates that certification standards should evolve to include advanced microbiome and metabolomic monitoring for early detection. |
| Differences in findings are attributed to study design, analytical approaches, population diversity, and combined exposures. Most studies focus on single metals, but real-life exposures are typically mixed. | Underlines the need for comprehensive, multi-metal risk assessments and harmonized analytical standards for certification. |
Key implications
The review clearly shows that even low-level exposure to heavy metals can disrupt the gut microbiota and related health outcomes, supporting rigorous limits and monitoring in heavy metal certification programs. Certification should account for cumulative, mixed-metal exposures, utilize advanced microbiome and metabolomic analyses as early biomarkers, and consider vulnerable populations and real-life exposure scenarios. The findings also highlight the dynamic interplay between essential and toxic metals and the importance of ongoing research to refine certification standards.
Citation
Giambò F, Italia S, Teodoro M, Briguglio G, Furnari N, Catanoso R, Costa C, Fenga C. Influence of toxic metal exposure on the gut microbiota (Review). World Acad Sci J. 2021;3:19. doi:10.3892/wasj.2021.90
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