Cadmium

Overview

Cadmium is a toxic non-essential heavy metal (IARC Group 1 carcinogen) with a biological half-life of 17—30 years in mammals, primarily accumulating in the renal cortex via proximal tubular reabsorption of the Cd-metallothionein complex [1], [2], [3]. With no known biological function, cadmium enters cells through transporters intended for essential metals —- divalent metal transporter 1 (DMT1, shared with iron), ZIP transporters (shared with zinc), and voltage-gated calcium channels —- a molecular mimicry that underlies both its toxicity and its ecological effects on the microbiome [4], [5].

What distinguishes cadmium in the WikiBiome framework is the convergence of three properties no other toxic metal combines to the same degree: (1) it is the most potent known metalloestrogen, (2) it creates functional zinc deficiency through competitive displacement across 300+ Zn-dependent enzymes, and (3) it reshapes the gut microbiome through selective pressure on metal-dependent taxa while simultaneously destroying the intestinal barrier that limits its own absorption —- a self-amplifying cycle.

Biological Roles

Cadmium has no essential biological function. Its toxicity operates through several interconnected mechanisms:

Oxidative stress. Cadmium generates reactive oxygen species (ROS) by inhibiting electron transport chain complexes II and III in mitochondria, collapsing membrane potential and activating the caspase cascade [2]. Simultaneously, Cd depletes the cellular antioxidant arsenal —- it binds glutathione via thiol groups, inhibits superoxide dismutase (SOD) by displacing zinc and manganese cofactors, and reduces catalase and glutathione peroxidase activity [3], [6]. The result is a synergistic toxicity: Cd induces oxidative stress while simultaneously disabling the enzymes that would neutralize it.

Epigenetic modification. Cd exposure alters DNA methylation patterns globally (hypomethylation with chronic exposure), modifies histone acetylation, and dysregulates microRNA expression. In MCF-7 breast cancer cells, Cd treatment altered 997 genes by epigenetic modification, 400 of which are associated with breast cancer [7]. Defective DNA repair following Cd-induced oxidative damage is considered a primary carcinogenic mechanism [3].

Metallothionein induction. The liver and kidneys synthesize metallothionein (MT) proteins (MW 7—8 kDa, containing 18—23 cysteine residues) that can complex 7 divalent cations. Cd binds MT with higher affinity than zinc, and the Cd-MT complex has a half-life of 25—30 years, accounting for cadmium's extraordinary persistence in biological tissue [2]. MT overexpression predicts cancer progression and drug resistance [7].

Dietary and Environmental Sources

Diet accounts for approximately 90% of non-occupational cadmium exposure. A large Chinese population study (n=56,191) found that diet contributes 59.78% of total Cd intake (mean 4.62 ug/day of 7.73 ug/day total), with smoking contributing 37.84%, water 1.91%, and air 0.47% [8].

  • Grains and rice: The largest dietary contributors in Asian populations, providing a mean of 1.55 ug Cd/day. Rice grown in contaminated paddies is especially high [8], [2].
  • Shellfish and organ meats: Naturally concentrate Cd through bioaccumulation. Vegetarians and shellfish consumers face higher Cd intake than omnivores [2].
  • Leafy vegetables, mushrooms, cocoa: Accumulate Cd from soil contamination; cocoa powder contains both significant Cd and significant polyphenols (3,450 mg/100g) [2].
  • Tobacco smoke: A single cigarette contains approximately 1 ug Cd, of which 40—60% is absorbed via inhalation. Smokers show 4—5x higher blood Cd levels [1], [7]. Smoking is the predominant determinant of non-essential metal levels in plasma [9].
  • Baby food contamination: Commercial baby foods across Italy, Brazil, Germany, and Nigeria contain detectable Cd alongside nickel, lead, and arsenic [10], [11]. The developmental vulnerability window means infant exposure has disproportionate long-term consequences [12].
  • Industrial sources: Ni-Cd batteries, pigments, electroplating, phosphate fertilizers.
  • Drinking water: Regulated under the EU Drinking Water Directive at 5 ug/L [13].

Geographic variation matters. Mean blood Cd in China (1.54 ug/L) is 3—4x higher than in European countries (Italy 0.53 ug/L, Germany 0.38 ug/L), with the highest levels in industrialized provinces: Henan (4.14), Shanxi (2.84), and Jiangxi (2.82 ug/L) [8].

Microbiome Interactions

The relationship between cadmium and the gut microbiome is bidirectional: Cd reshapes microbial communities through selective pressure, while the microbiome modulates Cd absorption, bioavailability, and toxicity [14], [15]. This bidirectional axis makes the gut the critical interface in cadmium toxicology.

Cd-Induced Dysbiosis

Across multiple animal models and a systematic review spanning 3,000+ subjects, cadmium exposure consistently disrupts gut microbiota composition [16]:

  • Enriched under Cd exposure: Prevotella, Treponema (in wild hamsters) [17]; Helicobacter, Campylobacter [15]; Proteobacteria at the phylum level [18]; Clostridia_UCG_014, NK4A214_group, Lachnospiraceae_NK4B4_group (in rats) [19]; Prevotella (from 0 to ~300 OTUs in ApoE4-KI mice on low Cd) [20]; Collinsella as a cross-metal pathobiont marker [16].
  • Depleted under Cd exposure: akkermansia muciniphila (at low doses) [21], [22]; Bacteroides ovatus [20]; Clostridium cocleatum (a beneficial commensal protecting against C. difficile) [20]; Clostridiaceae and Lactobacillaceae SCFA producers [20]; bifidobacterium [16]; butyrate-producing genera including blautia, Anaerostipes, Gemmiger, Intestinimonas [23]; Ruminococcaceae [24].
  • Diversity loss: Cd exposure caused a significant decrease in microbial alpha diversity (p=0.0028) in a controlled mouse study, with Bacteroidetes significantly decreased and Proteobacteria and Tenericutes increased [23].

The dysbiosis pattern is not random. Cd selects for metal-tolerant organisms while eliminating metal-sensitive ones —- a direct demonstration of metals as selective pressures. Microbial communities under metal stress adopt three functional roles: sensitive (eliminated by metal), resistant (survive via efflux and sequestration), and actor (actively reduce metal bioavailability, improving conditions for sensitive species) [25].

Metal-Specific Microbiome Effects Compared

In a head-to-head comparison of five toxic metals given to rats by oral gavage, cadmium affected only 5 genera (compared to nickel's 37), but produced significant dose-dependent compositional shifts (PERMANOVA) [26]. This narrower but consistent taxonomic effect distinguishes Cd from the broader disruption caused by nickel and arsenic.

Metabolomic Consequences of Cd-Induced Dysbiosis

Cd-driven microbial disruption cascades into measurable metabolite shifts:

  • Short-chain fatty acid (SCFA) depletion: Cd decreases fecal acetate, propionate, and butyrate by depleting SCFA-producing taxa [14], [20].
  • Uremic toxin accumulation: Cd exposure upregulates indoxyl sulfate, p-cresol sulfate, and phenol sulfate —- known uremic toxins and CVD risk factors —- linking Cd-induced dysbiosis to cardiovascular risk [19].
  • Amino acid disruption: Valine, aspartic acid, methionine, tyrosine, and norleucine are differentially abundant under Cd exposure [23].
  • Bile acid perturbation: Cd shifts bile acid homeostasis, compounding the metabolic consequences of taxonomic disruption [23].
  • Catecholamine precursor disruption: In children, Cd exposure correlates with altered microbiome-associated phenylalanine and tyrosine metabolites, predicting behavioral outcomes (r=-0.38, p=0.003 for Cd-social behaviour correlation) [27].

Gut Barrier Destruction --- The Vicious Cycle

Cadmium destroys the intestinal barrier through direct reduction of tight junction proteins: ZO-1, ZO-2, JAM-A, occludin, and claudin-1 [21], [28]. In Caco-2 and T84 intestinal cell lines, Cd at 20 uM reduced transepithelial electrical resistance (TEER) dose-dependently; at 68 uM, resistance was abolished entirely [29]. Inflammatory cytokines TNF-alpha and IL-6 increase significantly in both intestine and blood following Cd exposure [19].

This creates a self-amplifying loop: Cd damages the barrier, increasing permeability, which increases Cd absorption, which further damages the barrier. The loop also enables bacterial translocation —- in Cd-exposed rats, gut bacteria (Muribaculaceae) translocated into the blood, directly demonstrating how Cd-induced barrier failure enables microbial invasion of the circulatory system [19].

Germ-free mice accumulate significantly more Cd in organs than conventional mice, demonstrating that the intact microbiome is itself a defense against metal absorption [21].

Probiotic Protection

The microbiome is not merely a victim of Cd toxicity —- it is also a first line of defense. Several probiotic strategies have demonstrated protection against Cd:

  • L. plantarum CCFM8610 protects through four mechanisms: intestinal Cd sequestration (binding before absorption), oxidative stress alleviation, tight junction protection (restoring ZO-1, ZO-2, occludin, claudin-1), and immune modulation (restoring sIgA, modulating TNF-alpha, IL-1beta, IL-6, IL-8, IL-10). Key insight: strains with both metal-binding and antioxidative capacity were superior to strains with only one property [28].
  • Pediococcus acidilactici GR-1 in an RCT of occupational workers (n=152) reduced blood metal levels through gut microbiome-mediated metal excretion, enriched Blautia species (SCFA producers), decreased pro-inflammatory IL-6 and IL-1beta, and increased fecal SCFA production [30].
  • FMT from probiotic-enriched donors significantly increased fecal Cd excretion (0.2147 vs 0.123 mg/L, p<0.05) in Cd-exposed rats, demonstrating enhanced Cd clearance via microbial binding. The mechanism involves gram-positive bacteria binding Cd to cell wall peptidoglycan and teichoic acid [4].

Bacterial Resistance and Metabolic Reprogramming

Individual bacterial species respond to Cd stress in dramatically different ways:

  • Enterococcus faecium CX 2-6 responds to Cd with massive transcriptional reprogramming: 1,152 differentially expressed genes (47% of the genome). The response proceeds in phases —- nucleotide metabolism shutdown, translation upregulation, then defense via P-type ATPase efflux pumps and exopolysaccharide (EPS) production for extracellular Cd sequestration. This is a conserved core-genome strategy across 138 E. faecium strains [31].
  • Acinetobacter baumannii uses the CDF transporter CzcE (upregulated ~480-fold by the CadR sensor) to export Cd from cytoplasm to periplasm, then the HME system CzcCBA to export it extracellularly. A 67-gene cadmium resistome was identified by TraDIS. Critically, Cd stress caused zinc depletion (below detection at 15 uM Cd) and copper hyperaccumulation, demonstrating cross-metal disruption [32].
  • Vibrio parahaemolyticus uses the ZntA P-type ATPase for Cd efflux. ZntA expression is induced ~19-fold by Cd. Ferrous iron supplementation at 0.25 mM rescued growth under Cd excess, revealing iron-zinc-cadmium cross-talk where iron can compensate for Cd-mediated zinc homeostasis defects [5].

Nutritional Immunity

Cadmium's toxicity intersects with the host's nutritional immunity system in several ways:

Cd enters through essential metal transporters. DMT1 (the primary non-heme iron transporter) also imports Cd. Low iron availability and acidic pH increase DMT1 expression, paradoxically enhancing Cd uptake —- making iron-deficient individuals more vulnerable to Cd absorption [4], [33]. ZIP14, a zinc transporter in the small intestine and kidneys, is another route; Cd downregulates ZIP14, reducing zinc bioavailability and creating functional zinc deficiency even with adequate dietary zinc [24].

Convergence with host zinc weaponization. In Streptococcus pneumoniae, Cd competes with manganese for the PsaA permease —- the same transporter that host zinc targets during nutritional immunity. At 30 uM, Cd reduces intracellular Mn and Zn by ~70%, causing widespread enzyme dysfunction [6]. This convergence of environmental Cd toxicity and host zinc defense on the same transporter demonstrates that PsaA is a critical vulnerability node.

Glutathione as the Cd buffer. Glutathione serves as the primary intracellular Cd chelator, binding free Cd via thiol groups. When glutathione is depleted —- whether by genetic mutation, oxidative stress, or Cd overload itself —- the cell loses its defense against Cd-mediated mis-metallation. Strains of S. pneumoniae with impaired glutathione synthesis show dramatically increased Cd sensitivity [6].

Cd-Zn Competition and Mis-metallation

Cadmium and zinc share similar ionic radius and coordination chemistry, enabling Cd to substitute for Zn in metalloenzymes, transcription factors, and structural proteins. This competition is the molecular engine of much of Cd's pathology.

Proteome-wide mis-metallation. The most comprehensive demonstration comes from S. pneumoniae, where Cd was shown to mis-metallate at least 16 metalloproteins, including glycolytic enzymes (enolase, phosphofructokinase) and superoxide dismutase (SOD). This forced metabolic rerouting from glycolysis to the pentose phosphate pathway —- a systems-level metabolic rewiring from a single toxic metal. The downstream consequence was altered membrane fatty acid composition and reduced capsule production (the primary virulence factor), potentially attenuating pathogenicity [34].

Functional zinc deficiency. Across cancer types, Cd elevation co-occurs with Zn depletion. A meta-analysis of 36 case-control studies (n=4,151) confirmed that Cd is significantly elevated in breast cancer patients (SMD 2.55 in Asia) while Zn is significantly depleted (SMD -2.09) [33]. The Cu/Zn ratio is proposed as a pan-cancer biomarker [35], [36]. In ASD, the same pattern recurs: toxic metals (Pb, Hg, Cd) elevated alongside consistent Zn depletion, with ~10% of the human genome encoding zinc-binding proteins that become vulnerable targets [37].

The Zn/Cd ratio as biomarker. In diabetic nephropathy, the zinc-to-cadmium ratio functions as a critical injury biomarker. A zinc-curcumin complex reversed Cd-induced dysbiosis and nephropathy in mice, with FMT from treated mice reproducing the effect —- confirming microbiome mediation of the Zn/Cd antagonism [24].

Bidirectionality. The competition is bidirectional: zinc deficiency exacerbates cadmium toxicity (more Cd enters through vacant Zn binding sites), and cadmium exposure induces functional zinc deficiency (Cd occupies Zn sites, rendering them nonfunctional). Prenatal zinc deficiency causes ASD-like behavior in mice, and prenatal zinc therapy prevents VPA-induced ASD-like behaviors —- connecting the Cd-Zn axis to neurodevelopmental outcomes [37].

Metalloestrogen Activity

Cadmium is the most potent known metalloestrogen. It binds estrogen receptor alpha (ERa) with a dissociation constant (Kd) of approximately 4.5 x 10^-10 M (picomolar affinity), near-equivalent to estradiol [38]. This binding:

  • Activates ER target genes (CycD1, c-myc, CTD) in breast cancer cell lines at concentrations as low as 1 uM [38]
  • Activates the membrane-bound estrogen receptor GPR30/GPER, inducing proliferative responses via ERK-1/2 at 50—500 nM in ER-negative cells
  • Chronic exposure (2.5 uM, 40+ weeks) transforms normal MCF-10A epithelial cells to a basal-like phenotype with increased invasive potential
  • Promotes epithelial-mesenchymal transition (EMT) by downregulating E-cadherin through Snail upregulation [7]
  • Disrupts the hypothalamic-pituitary-gonadal axis, affecting ovulation, steroidogenesis, and pituitary function [39]

nickel also shows metalloestrogen activity but with weaker epidemiological support [38].

Conditions Associated

Chronic Kidney Disease

The kidney is cadmium's primary chronic target organ. The Cd-metallothionein (Cd-MT) complex is filtered at the glomerulus and reabsorbed in proximal tubules, where lysosomal degradation at pH 4.5—5.5 releases free Cd, causing tubular damage [1]. Beta-2 microglobulin in urine serves as a biomarker for Cd-induced tubular toxicity (detectable at urinary Cd as low as 360 ug/L) [3].

The vicious cycle: Cd accumulates in renal cortex proportional to lifetime exposure; Cd impairs electron transport chain complexes II/III, inducing mitochondrial dysfunction and oxidative stress; tubular damage reduces GFR, impairing Cd elimination; declining renal function increases Cd retention, accelerating further damage [40].

Epidemiological evidence: Blood Cd >=0.4 ug/L independently associated with CKD risk (OR 1.23); combined elevated Pb + Cd shows highest risk (OR 1.65). Elevated Cd associated with 42% increased mortality in CKD patients (HR 1.42) [41]. A longitudinal study (n=384, 4 repeated measurements) found synergistic effects of Cd-Cr on renal biomarkers (NAG, UACR), and a triple synergistic effect of Pb-Cd-Cr on UACR. Females and smokers showed greater kidney damage at equivalent exposure levels [42].

Breast Cancer

Cd accumulates preferentially in the mammary gland. A meta-analysis of 36 studies (n=4,151) confirmed significantly higher Cd in plasma/serum of breast cancer patients [33]. The Cd-breast cancer relationship involves multiple mechanisms beyond estrogenicity:

  • Epigenetic: 997 genes altered by epigenetic modification in MCF-7 cells, 400 associated with breast cancer; chronic exposure leads to global DNA hypomethylation [7]
  • Oxidative: Cd inhibits DNA repair enzymes (hOGG1), disrupting NER and BER pathways
  • Metallothionein: MT overexpression predicts cancer progression and drug resistance
  • miRNA: miR-374c-5p inhibition, miR-30 downregulation (facilitating EMT), miR-21 upregulation (promoting proliferation) [7]
  • Cd enhanced mammary tumorigenesis in animal models when combined with gut microbiome disruption [15]

Cardiovascular Disease

An overview of 8 systematic reviews (153 studies, ~160,000+ participants) confirmed that Cd exposure independently increases risk of atherosclerosis, coronary artery disease, hypertension, myocardial infarction, and stroke [43]. Cd correlates with hypertension even at low concentrations (<1 ug/L plasma). The mechanism involves ROS generation, TNF-alpha and NF-kB p65 activation, NLRP3 inflammasome engagement, endothelial damage via reduced NO and increased endothelin-1 (EDN-1) [43].

Cd also drives cardiovascular risk indirectly through the microbiome: Cd-induced dysbiosis upregulates indoxyl sulfate production (a pro-atherogenic uremic toxin) and depletes Clostridium and Lactobacillus species that produce protective tryptophan metabolites (IPA, IAld) [1], [19].

Type 2 Diabetes

A burden-of-disease analysis across 46 studies (n=56,191) estimated that eliminating cadmium exposure would reduce T2D incidence by approximately 65% (population attributable fraction). The dose-response relationship is linear: RR of 1.47 at 1.5—2.0 ug/L blood Cd, 2.43 at 2.0—2.5 ug/L, and 4.00 at >2.5 ug/L [8]. Cd disrupts pancreatic beta-cell lipid metabolism, induces pancreatic inflammation, and alters glucose homeostasis. Cd aggravated diabetic nephropathy through TLR4/NF-kB activation in an animal model [24].

Neurodegenerative Disease

Cd enters neurons via voltage-gated calcium channels and diminishes glutathione peroxidase, catalase, and SOD activity. In humanized ApoE4-KI mice (an Alzheimer's model), Cd exposure caused gut microbiota changes —- increasing Prevotella (an AD microbial biomarker) and decreasing SCFA-producing Clostridiaceae and Lactobacillaceae —- and activated NF-kB/IL-1beta in the liver, disrupting the gut-liver axis [20]. Cd has been linked to Alzheimer's disease, Parkinson's disease, and multiple sclerosis through calcium signaling disruption and protein misfolding [44], [1].

In the Parkinson's context, Cd-driven enrichment of Proteobacteria (including iron-scavenging Enterobacteriaceae) mirrors the PD microbiome signature. Cd competes with iron for DMT1 and ZIP transporter uptake, dysregulating iron homeostasis in a pattern consistent with PD pathology [18].

Polycystic Ovary Syndrome (PCOS)

A systematic review of 15 controlled studies found consistently elevated Cd in women with PCOS (1.2 vs 0.7 ppb; 1.75 vs 0.59 ppb in two studies). Cd levels positively correlated with oxidative stress markers (MDA, TNF-alpha) and insulin resistance (HOMA-IR). The metalloestrogen activity of Cd disrupts the hypothalamic-pituitary-gonadal axis, contributing to the hormonal dysregulation characteristic of PCOS [45].

Autism Spectrum Disorder

A comprehensive narrative review of 25+ studies across multiple biomatrices found Cd elevated in hair and urine of individuals with ASD. The proposed mechanism centers on Cd competing with zinc for binding sites across the ~10% of human genome that encodes zinc-binding proteins, creating functional zinc deficiency during critical neurodevelopmental windows. Key synaptic ASD-associated pathways (NLGN-NRXN-SHANK, mTOR/PI3K) are modified by zinc and calcium and are vulnerable to toxic metal displacement [37].

Female Infertility

In a population-based analysis (NHANES 2013—2016), a two-fold increase in blood Cd was associated with 1.84-fold increased odds of infertility (95% CI 1.07—3.15) after full adjustment. Effects were observed even at low blood metal levels (geometric mean Cd = 0.26 ug/L) [39]. Cd affects ovulation, steroidogenesis, and pituitary function through both metalloestrogen activity and direct gonadotoxicity.

Inflammatory Bowel Disease

Short-term Cd exposure (1 week) exacerbated acute colitis in mice, but paradoxically, subchronic (6-week) exposure showed protective effects through metallothionein induction and immunomodulation —- reducing IL-6, IL-1beta, and Nos2 transcription while upregulating TGF-beta. This hormesis-like dose-duration response challenges simple dose-response assumptions in Cd toxicology [29].

Male Reproductive Toxicity

FMT from probiotic-enriched donors reversed Cd-induced testicular degeneration in rats, restoring sperm motility from 23% to 53%, concentration from 1.98 x 10^7 to 1.14 x 10^8/mL, and serum testosterone from 2.053 to 4.54 ng/mL. Cd enters testes via ZIP8 and CatSper channels (mimicking Ca2+), disrupting the blood-testis barrier and Leydig cell function [4].

Itai-Itai Disease

The historical epidemic of cadmium poisoning in Toyama Prefecture, Japan (1910s—1960s) produced itai-itai ("it hurts-it hurts") disease —- severe osteomalacia with renal tubular dysfunction. Cd interferes with calcium metabolism and bone mineralization, causing pathological fractures. This remains the most dramatic example of chronic dietary cadmium poisoning [1].

Metal-Antibiotic Co-resistance

Enterococcus species carry metal tolerance (MeT) genes for mercury, arsenic, and copper that co-occur with antibiotic resistance (ABR) genes on mobile genetic elements. MeT genes have been present since at least the 1900s, but co-occurrence with ABR genes has increased since the 1990s. These resistance cassettes transfer horizontally across genera [46].

Three molecular mechanisms drive co-selection: (1) co-resistance —- physical linkage on the same plasmid or transposon; (2) cross-resistance —- the same gene conferring resistance to both (e.g., CzcCBA system expelling Co, Zn, Cd and certain antibiotics); and (3) co-regulatory mechanisms —- shared transcriptional responses [47]. Heavy metals, unlike antibiotics, are non-degradable and represent a permanent selective pressure in contaminated environments.

Biomarkers

BiomarkerWhat it reflectsReference valuesKey findings
Blood CdRecent exposure (half-life ~3—4 months)<0.4 ug/L normal; >5 ug/L pathologic>=0.4 ug/L associated with CKD risk (OR 1.23) [41]
Urine CdCumulative body burden, tubular damageBiologically permissible 0.0445 mol/LPrevalence 2.3% elevated in US population [41]
Urine beta-2 microglobulinProximal tubular damageDetectable at urinary Cd ~360 ug/LEarliest biomarker of Cd nephrotoxicity [3]
Blood Cd in CKDDisease progressionMean 0.60 vs 0.53 in non-CKD (p<0.01)HR 1.42 for mortality [41]
Smoker blood CdTobacco-specific exposure4—5x non-smoker levelsDominant determinant of plasma toxic metals [9]
Tissue CdLifetime accumulationRenal cortex proportional to ageMammary tissue elevated in breast cancer [7]
Zn/Cd ratioFunctional zinc status under Cd burdenDeclining ratio indicates injuryBiomarker for diabetic nephropathy severity [24]

Key Studies

  • Rezazadegan et al. 2025 (systematic review, n=3,000+): Universal dysbiosis across Cd and other heavy metals; Collinsella enriched as pathobiont marker [16]
  • Nucera et al. 2024 (overview of 8 systematic reviews, ~160,000+ participants): Cd independently increases CVD risk including hypertension at <1 ug/L plasma [43]
  • Liu et al. 2022 (meta-analysis, 36 studies, n=4,151): Cd elevated, Zn depleted in breast cancer across five continents [33]
  • Li et al. 2023 (burden-of-disease, n=56,191): PAF ~65% for Cd-attributable diabetes; dose-response RR up to 4.00 at >2.5 ug/L [8]
  • Neville et al. 2020 (in-vitro): 16+ mis-metallated proteins in pneumococcus; glycolysis rerouted to pentose phosphate pathway; capsule production reduced [34]
  • Feng et al. 2022 (RCT, n=152): Probiotic yogurt reduced blood metals through gut microbiome-mediated excretion in occupational workers [30]
  • Baker-Austin et al. 2006 (seminal review): Established the three-mechanism framework for metal-antibiotic co-selection [47]

Cross-References

  • nickel — co-occurring heavy metal; both are metalloestrogens, both disrupt tight junctions
  • zinc — competitive binding; Cd-induced Zn displacement is a primary toxicity mechanism
  • iron — shares DMT1 transporter with Cd; iron deficiency enhances Cd absorption
  • manganese — Cd displaces Mn from PsaA and SOD, compounding oxidative vulnerability
  • lead — synergistic toxicity with Cd, especially for CKD and mortality risk
  • oxidative stress — central mediator of Cd toxicity across all organ systems
  • glutathione — Cd depletes GSH via thiol binding; GSH depletion amplifies oxidative damage
  • mis metallation — Cd displaces Zn/Mn/Ca from metalloproteins; 16+ targets mapped in pneumococcus
  • nutritional immunity — Cd exploits the same transporters used by host metal weaponization
  • co selection — Cd contamination drives antibiotic resistance via co-resistance and cross-resistance
  • akkermansia muciniphila — depleted at low Cd doses; paradoxically increased in some Alzheimer's models
  • blautia — enriched by probiotic intervention against Cd; depleted by Cd exposure
  • cardiovascular disease — endothelial damage, atherosclerosis, uremic toxin accumulation
  • colorectal cancer — Cd in the cancer metallomics landscape
  • metal disease matrix — Cd appears across multiple disease columns
  • metal carcinogenesis — epigenetic carcinogenesis, metalloestrogen activity
  • ovarian cancer — Cd as metalloestrogen binding ERa; ovarian tissue accumulation
  • gastric cancer — Cd elevated in gastric cancer tissue
  • metal chelation therapy — EDTA and DMSA used for Cd poisoning; limited efficacy due to renal Cd accumulation
  • environmental metal exposure — dietary and tobacco Cd are the dominant non-occupational exposure routes
  • heavy metals — Cd is among the most toxic heavy metals with a 25—30 year biological half-life
  • biomarkers — urinary Cd and blood Cd as exposure biomarkers; beta-2-microglobulin for nephrotoxicity
  • ferroptosis — iron-dependent cell death in Cd-damaged renal tubular cells
  • estrobolome — Cd mimics estradiol at picomolar affinity; same glucuronidase enzymes mediate estrogen and androgen recirculation

References (50)

  1. ★Puthiyavalappil Rasin, Ashwathi A V, Sabeel M Basheer et al. (2025). Exposure to Cadmium and Its Impacts on Human Health: A Short Review. Journal of Hazardous Materials Advances. doi:10.1016/j.hazadv.2024.100527
  2. Giuseppe Genchi, Maria Stefania Sinicropi, Graziantonio Lauria et al. (2020). The Effects of Cadmium Toxicity. International Journal of Environmental Research and Public Health. doi:10.3390/ijerph17113782
  3. ★Balali-Mood M, Naseri K, Tahergorabi Z et al. (2021). Toxic Mechanisms of Five Heavy Metals: Mercury, Lead, Chromium, Cadmium, and Arsenic. Frontiers in Pharmacology. doi:10.3389/fphar.2021.643972
  4. Aditi Ghosh (2023). Ghosh 2023 — Evaluation of Therapeutic Efficacy of Fecal Microbiota Transplantation on Cadmium-Induced Testicular Degeneration in Rats. M.Sc. Thesis, ICAR-National Dairy Research Institute (Deemed University)
  5. Chengkun Zheng, Yimeng Zhai, Jun Qiu et al. (2024). Zheng 2024 — ZntA Maintains Zinc and Cadmium Homeostasis and Promotes Oxidative Stress Resistance and Virulence in Vibrio parahaemolyticus. Gut Microbes. doi:10.1080/19490976.2024.2327403
  6. Stephanie L. Begg, Bart A. Eijkelkamp, Zhenyao Luo et al. (2015). Begg et al. 2015 — Dysregulation of Transition Metal Ion Homeostasis Is the Molecular Basis for Cadmium Toxicity in Streptococcus pneumoniae. Nature Communications. doi:10.1038/ncomms7418
  7. Tarhonska K, Lesicka M, Janasik B et al. (2022). Cadmium and breast cancer - Current state and research gaps in the underlying mechanisms. Toxicology Letters. doi:10.1016/j.toxlet.2022.03.003
  8. Shan Li, Muhadasi Tuerxunyiming, Zhe Sun et al. (2023). Li 2023 — Burden of diabetes attributable to dietary cadmium exposure in adolescents and adults in China. Environmental Science and Pollution Research. doi:10.1007/s11356-023-29424-6
  9. Si Ying Lim, Hiranya Dayal, Song Jie Seah et al. (2023). Plasma metallomics reveals potential biomarkers and insights into the ambivalent associations of elements with acute myocardial infarction. Journal of Trace Elements in Medicine and Biology. doi:10.1016/j.jtemb.2023.127148
  10. Maria Assunta Meli, Donatella Desideri, Davide Sisti et al. (2024). Meli 2024 — Chemical characterization of baby food consumed in Italy. PLOS ONE. doi:10.1371/journal.pone.0297158
  11. Cristine Couto de Almeida, Diego dos Santos Baiao, Paloma de Almeida Rodrigues et al. (2022). Toxic Metals and Metalloids in Infant Formulas Marketed in Brazil, and Child Health Risks According to the Target Hazard Quotients and Target Cancer Risk. International Journal of Environmental Research and Public Health. doi:10.3390/ijerph191811178
  12. Karen Pendergrass (2026). Age-Window Metabolic and Toxicokinetic Vulnerability in Vegetable-Based Baby Foods: Separating Developmental Readiness from Toxicant Susceptibility. Zenodo Preprint. doi:10.5281/zenodo.18366816
  13. European Parliament, Council of the European Union (2020). Directive (EU) 2020/2184 on the Quality of Water Intended for Human Consumption (Recast). Official Journal of the European Union (L 435/1)
  14. ★Hui Duan, Leilei Yu, Fengwei Tian et al. (2020). Gut Microbiota: A Target for Heavy Metal Toxicity and a Probiotic Protective Strategy. Science of the Total Environment. doi:10.1016/j.scitotenv.2020.140429
  15. ★Qinheng Zhu, Boyan Chen, Fu Zhang et al. (2024). Toxic and Essential Metals: Metabolic Interactions with the Gut Microbiota and Health Implications. Frontiers in Nutrition. doi:10.1016/j.biopha.2023.115602
  16. Fatemeh Rezazadegan, Maryam Mahmoudi, Seyed Mohammad Mousavi (2025). Rezazadegan et al. 2025 — Heavy Metals and Gut Microbiota: A Systematic Review. Journal of Health, Population and Nutrition. doi:10.1186/s41043-025-00750-4
  17. Mengfan Tao, Kanglin Cao, Xinsheng Pu et al. (2024). Tao 2024 — Cadmium exposure induces changes in gut microbial composition and metabolic function in long-tailed dwarf hamsters. Ecology and Evolution. doi:10.1002/ece3.11682
  18. Pengya Zhang, Huizhen Zheng, Guangbo Qu (2021). Zhang 2021 -- Cadmium Exposure and Gut Microbiome Disruption in Neurodegeneration. Communications Biology. doi:10.1038/s42003-021-02898-1
  19. Songqing Liu, Xin Deng, Zheng Li et al. (2023). Environmental cadmium exposure alters the internal microbiota and metabolome of Sprague-Dawley rats. Frontiers in Veterinary Science. doi:10.3389/fvets.2023.1219729
  20. Angela Zhang, Megumi Matsushita, Liang Zhang et al. (2021). Cadmium exposure modulates the gut-liver axis in an Alzheimer's disease mouse model. Communications Biology. doi:10.1038/s42003-021-02898-1
  21. ★Sweta Ghosh, Syam P. Nukavarpu, Venkatakrishna Rao Jala (2023). Effect of Heavy Metals on Gut Barrier Integrity and Gut Microbiota. Metal ions in Life Sciences (Accepted Manuscript)
  22. ★Federica Giambo, Sebastiano Italia, Michele Teodoro et al. (2021). Influence of Toxic Metal Exposure on the Gut Microbiota (Review). World Academy of Sciences Journal
  23. Xuanji Li, Asker Daniel Brejnrod, Madeleine Ernst et al. (2019). Heavy Metal Exposure Causes Changes in the Metabolic Health-Associated Gut Microbiome and Metabolites. Environment International. doi:10.1016/j.envint.2019.05.048
  24. Yujie Sun, Xiaoyu Zhang, Yingying Liu et al. (2024). Sun et al. 2024 — Zinc-Curcumin Complex Reverses Cadmium-Aggravated Diabetic Nephropathy via Microbiome Mediation. Frontiers in Pharmacology. doi:10.3389/fphar.2024.1411230
  25. Chen X, Zhao Y, Zhao X et al. (2020). Selective pressures of heavy metals on microbial community determine microbial functional roles during composting: Sensitive, resistant and actor. Journal of Hazardous Materials. doi:10.1016/j.jhazmat.2020.122858
  26. Richardson JB, Dancy BCR, Horton CL et al. (2018). Exposure to toxic metals triggers unique responses from the rat gut microbiota. Scientific Reports. doi:10.1038/s41598-018-24931-w
  27. Kristin Krajewski (2025). Krajewski 2025 -- Heavy metals, noradrenaline/adrenaline ratio, and microbiome-associated hormone precursor metabolites: biomarkers for social behaviour, ADHD symptoms, and executive function in children. Scientific Reports. doi:10.1038/s41598-025-00680-5
  28. ★Zhai Q, Wang G, Zhao J et al. (2016). Oral Administration of Probiotics Inhibits Absorption of the Heavy Metal Cadmium by Protecting the Intestinal Barrier. Appl Environ Microbiol. doi:10.1038/s41420-023-01587-8
  29. Breton J, Daniel C, Vignal C et al. (2016). Does oral exposure to cadmium and lead mediate susceptibility to colitis? The dark-and-bright sides of heavy metals in gut ecology. Scientific Reports. doi:10.1038/srep19200
  30. Feng P, Yang J, Zhao S et al. (2022). Feng 2022 — Human supplementation with Pediococcus acidilactici GR-1 decreases heavy metal levels through modifying the gut microbiota and metabolome. npj Biofilms and Microbiomes. doi:10.1038/s41522-022-00326-8
  31. Cheng X, Yang B, Zheng J et al. (2021). Cadmium stress triggers significant metabolic reprogramming in Enterococcus faecium CX 2-6. Computational and Structural Biotechnology Journal. doi:10.1016/j.csbj.2021.10.021
  32. Alquethamy SF, Adams FG, Maharjan R et al. (2021). The Molecular Basis of Acinetobacter baumannii Cadmium Toxicity and Resistance. Applied and Environmental Microbiology. doi:10.1128/AEM.01718-21
  33. ★Liu L, Chen J, Liu C et al. (2022). Relationships Between Biological Heavy Metals and Breast Cancer: A Systematic Review and Meta-Analysis. Frontiers in Nutrition. doi:10.3389/fnut.2022.838869
  34. Stephanie L. Neville, Jacqueline R. Morey, Erin B. Gillen et al. (2020). Neville et al. 2020 — Cadmium Stress Dictates Central Carbon Flux and Alters Membrane Composition in Streptococcus pneumoniae. Communications Biology. doi:10.1038/s42003-020-01417-y
  35. Yan Zhang, Jie He, Jiao Jin et al. (2022). Recent advances in the application of metallomics in diagnosis and prognosis of human cancer. Metallomics. doi:10.1007/s10653-023-01737-y
  36. Rie Sugimoto, Lingaku Lee, Yuki Tanaka et al. (2024). Zinc Deficiency as a General Feature of Cancer: A Review of the Literature. Biological Trace Element Research. doi:10.1007/s12011-024-04062-w
  37. Blazewicz A, Grabrucker AM (2023). Metal Profiles in Autism Spectrum Disorders: A Crosstalk between Toxic and Essential Metals. International Journal of Molecular Sciences. doi:10.3390/ijms24010308
  38. ★Aquino NB, Sevigny MB, Sabangan J et al. (2012). Role of Cadmium and Nickel in Estrogen Receptor Signaling and Breast Cancer: Metalloestrogens or Not?. Journal of Environmental Science and Health Part C - Environmental Carcinogenesis and Ecotoxicology Reviews. doi:10.1080/10590501.2012.705159
  39. Lee S, Min JY, Min KB (2020). Female Infertility Associated with Blood Lead and Cadmium Levels. International Journal of Environmental Research and Public Health. doi:10.5772/intechopen.89462
  40. ★Manish Mishra, Larry Nichols, Aditi A. Dave et al. (2022). Molecular Mechanisms of Cellular Injury and Role of Toxic Heavy Metals in Chronic Kidney Disease. International Journal of Molecular Sciences. doi:10.3390/ijms23063997
  41. Kuo PF, Huang YT, Chuang MH et al. (2024). Association of low-level heavy metal exposure with risk of chronic kidney disease and long-term mortality. PLOS ONE
  42. Yin G, Zhao S, Zhao M et al. (2024). Complex interplay of heavy metals and renal injury: New perspectives from longitudinal epidemiological evidence. Ecotoxicology and Environmental Safety. doi:10.23749/mdl.v114i3.14422
  43. Nucera S, Serra M, Caminiti R et al. (2024). Nucera 2024 — Non-essential heavy metal effects in cardiovascular diseases: overview of systematic reviews. Frontiers in Cardiovascular Medicine. doi:10.3389/fcvm.2024.1332339
  44. ★Bakulski KM, Seo YA, Hickman RC et al. (2020). Heavy Metals Exposure and Alzheimer's Disease and Related Dementias. Journal of Alzheimer's Disease. doi:10.3233/JAD-200282
  45. Smovrsnik T, Virant-Klun I, Pinter B (2023). Heavy Metals and Essential Elements in Association with Oxidative Stress in Women with Polycystic Ovary Syndrome -- A Systematic Review. Antioxidants. doi:10.3390/antiox12010049
  46. Rebelo A, Mourao J, Freitas AR et al. (2021). Diversity of metal and antibiotic resistance genes in Enterococcus spp. from the last century reflects multiple pollution and genetic exchange among phyla from overlapping ecosystems. Science of the Total Environment. doi:10.1016/j.scitotenv.2020.142710
  47. Baker-Austin C, Wright MS, Stepanauskas R et al. (2006). Baker-Austin 2006 — Co-selection of Antibiotic and Metal Resistance. Trends in Microbiology. doi:10.1016/j.tim.2006.02.006
  48. Xing Yan, Jun Qiu, Ruiwen Huang et al. (2025). Yan 2025 — Association Between Infants' Serum Levels of 26 Metals and Gut Microbiota: A Hospital-Based Cross-Sectional Study in China. Frontiers in Microbiology. doi:10.3389/fmicb.2025.1669475
  49. Aguilera M, Lamas B, Van Pamel E et al. (2021). Editorial: Risk of dietary hazardous substances and impact on human microbiota: possible role in several dysbiosis phenotypes. Frontiers in Microbiology. doi:10.3389/fmicb.2021.669480
  50. Liu S, Deng X, Li Z et al. (2023). Liu 2023 — Environmental cadmium exposure alters the internal microbiota and metabolome of Sprague–Dawley rats. Frontiers in Veterinary Science. doi:10.3389/fvets.2023.1219729

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