Nickel

Chemical Properties#

Transition metal (element 28), most commonly found as nickel (Ni)(II); atomic weight 58.69; five stable isotopes (58Ni at 68.077%, 60Ni, 61Ni, 62Ni, 64Ni).^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓} Density 8.912 g/cm3; melting point 1455C; boiling point 2913C.

Similar ionic radius to iron (Fe)(II), allowing it to substitute for iron in enzyme active sites—a key mechanism in its toxicity Hypoxic Signaling (HIF-1α Pathway), iron homeostasis disruption.^{[2]Genetic and Epigenetic Mechanisms in Metal Carcinogenesis and Cocarcinogenesis: Nickel, Arsenic, and ChromiumKonstantin Salnikov, Anatoly Zhitkovich · 2008Open reference 2 ↓}

Position in the Irving-Williams series (manganese (Mn) < iron < cobalt (Co) < nickel < copper (Cu) > zinc (Zn)): nickel binds biological ligands more tightly than iron, cobalt, or manganese, meaning it will preferentially displace these weaker-binding metals from enzyme active sites when concentrations rise—a process called Mis-Metallation.^{[3]Robinson & Glasfeld 2020 — Metalation and Mis-metalation: Nature's Challenge in Metal CoordinationNigel J. Robinson, Andrea Glasfeld · 2020Open reference 3 ↓}

Cells normally prevent this by keeping free nickel at extremely low concentrations, but dietary or environmental loading overwhelms these homeostatic buffers.^{[4]Capdevila 2024 — Bacterial Metallostasis: Metal Sensing, Metalloproteome Remodeling, and Metal TraffickingDaiana A. Capdevila, Johnma J. Rondon, Katherine A. Edmonds et al. · 2024Open reference 4 ↓}

Forms coordination complexes with cysteine, Histidine, glutamate, and lysine residues, enabling protein binding and enzyme inhibition.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Histidine is a particularly important nickel-chelating amino acid; supplementation with histidine rescues E. coli growth under combined nickel/copper stress by chelating free metal ions extracellularly.^{[6]Darwiche 2025 — The Molecular Basis of the Synergistic Toxicity of Nickel and Copper, Common Environmental Co-ContaminantsLinda Darwiche, Carlos A Rodriguez-Bornot, Rebecca A Ingrassia et al. · 2025Open reference 6 ↓}

The fifth most abundant element on Earth.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓} Ubiquitous in environment from both natural processes and anthropogenic activities (fossil fuel combustion, fertilizers, industrial emissions); found in air, water, soil, sediment, and particulate matter.^{[7]Cardio-Metabolic Effects of Nickel: A Narrative ReviewYucheng Liu, Xiaomin Luo, Yongde Peng et al. · 2025Open reference 7 ↓}

Atmospheric levels range from 0.00001-0.003 ug/m3 (remote), 0.003-0.03 ug/m3 (urban), up to 0.07-0.77 ug/m3 (metallurgical areas);^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓} cigarette smoke contains 1.1-3.1 ug nickel per cigarette.^{[9]Nickel essentiality, toxicity, and carcinogenicityDenkhaus E, Salnikov K · 2002Open reference 9 ↓[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Nickel Metabolism and Biomarkers#

Body burden: approximately 7.3 ug nickel (Ni)/kg body weight in healthy adults.^{[9]Nickel essentiality, toxicity, and carcinogenicityDenkhaus E, Salnikov K · 2002Open reference 9 ↓}

Average dietary intake: 150-350 ug/day in Western diets; potentially higher in plant-based and Indian diets.^{[10]Nickel Content of Food and Estimation of Dietary IntakeFlyvholm MA, Nielsen GD, Andersen A · 1984Open reference 10 ↓[9]Nickel essentiality, toxicity, and carcinogenicityDenkhaus E, Salnikov K · 2002Open reference 9 ↓} Beneficial intake estimated at <100 ug/day; most individuals achieve this only because 70 ug/day is typical minimum.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Absorption: only 1-10% of ingested nickel is absorbed from the GI tract; bioavailability varies by food matrix. Iron deficiency increases nickel absorption via shared DMT-1 (divalent metal transporter-1) pathways.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓[11]Toxicity, Mechanism and Health Effects of Some Heavy MetalsMonisha Jaishankar, Tenzin Tseten, Naresh Anbalagan et al. · 2014Open reference 11 ↓}

Serum levels: 0.2-7 ug/L depending on source; transported bound to nickeloplasmin, albumin, amino acids (especially histidine), and alpha-2-macroglobulin.^{[12]Systemic Nickel Allergy SyndromeDi Gioacchino M, Gatta A, Della Valle L et al. · 2018Open reference 12 ↓[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Tissue distribution: nickel accumulates in lungs, thyroid, adrenal glands, brain, kidneys, heart, liver, spleen, and pancreas.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Urinary nickel (UNi) is the primary biomarker in epidemiological studies; half-life 20-60 hours. Normal urine concentrations <10 ug/L; blood nickel >0.3 ug/L (may exceed 8 ug/L in exposed workers).^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Sweat nickel can reach 7-270 ug/L (up to 20x plasma levels), explaining why sweating aggravates nickel dermatitis.^{[12]Systemic Nickel Allergy SyndromeDi Gioacchino M, Gatta A, Della Valle L et al. · 2018Open reference 12 ↓} Acute toxicity: oral doses >0.5 g cause poisoning; doses approaching 1 g can be lethal.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Nickel enters cells via calcium(II) (Ca2+) channels, DMT-1 (shared with iron), and phagocytosis of particulate forms.^{[9]Nickel essentiality, toxicity, and carcinogenicityDenkhaus E, Salnikov K · 2002Open reference 9 ↓[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Insoluble nickel particles are phagocytosed based on surface charge—crystalline NiS (negative surface charge, -27 mV) binds cell membranes readily and is phagocytosed at much higher rates than amorphous NiS (positive charge, +9 mV), directly determining carcinogenic potency.^{[13]Specific Nickel Compounds as CarcinogensCosta M, Heck JD · 1982Open reference 13 ↓}

Carcinogenesis#

IARC Group 1 carcinogen (nickel compounds; metallic nickel is Group 2B).^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓} Causes lung and nasal cavity cancers in occupationally exposed workers.

Primary carcinogenic mechanism is epigenetic rather than genotoxic: DNA hypermethylation, histone modifications (deacetylation, H3K9 methylation, heterochromatinization at tumor suppressor loci), Hypoxic Signaling (HIF-1α Pathway) via HIF-1 stabilization.^{[2]Genetic and Epigenetic Mechanisms in Metal Carcinogenesis and Cocarcinogenesis: Nickel, Arsenic, and ChromiumKonstantin Salnikov, Anatoly Zhitkovich · 2008Open reference 2 ↓[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Nickel substitutes for iron(II) (Fe2+) in non-heme iron dioxygenases involved in DNA and histone demethylation—a key Epigenetic Modifications mechanism.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Acts as a cocarcinogen with UV radiation. Nickel-induced apoptosis occurs through both intrinsic (mitochondrial/Cyt C) and extrinsic (Fas/FasL) pathways, converging on caspase-3/6/7.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓} Can interfere with microRNA networks.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Genotoxicity: nickel disrupts DNA strands, causes crosslinks, and inhibits DNA repair. In HL-60 leukemia cells, long-term nickel(II) (Ni2+) exposure leads to DNA fragmentation, ROS generation, and cell death (preventable by ascorbic acid or N-acetyl-cysteine).^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

Nickel was the only metal tested to induce DNA damage at concentrations that induced >50% apoptosis (i.e., <0.05 mM) compared to vanadium.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

8-Hydroxydeoxyguanosine (8-OH-dG) formation: Ni3S2 significantly increases 8-OH-dG in cultured HeLa cells and elevates testicular lipid peroxides while decreasing antioxidant enzyme activities.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

Nickel stimulates L1 retrotransposition ~2.5-fold, representing a novel genotoxic mechanism via transposon mobilization distinct from direct DNA damage.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

Transcription factor disruption: nickel alters p53, NF-kB, AP-1, TGF-beta, and NF-AT; downregulates p53 and activates c-Myc.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Carcinogenicity by Compound#

Different nickel compounds have very different carcinogenic potentials, a principle established by Costa's foundational 1982 work demonstrating that phagocytosis is the primary determinant of cell transformation.^{[13]Specific Nickel Compounds as CarcinogensCosta M, Heck JD · 1982Open reference 13 ↓[16]Carcinogenicity Assessment of Selected Nickel CompoundsOller AR, Costa M, Oberdörster G · 1997Open reference 16 ↓}

Crystalline nickel sulfide (NiS): induces morphological transformation at rates 100x higher than amorphous NiS (24% vs. essentially none). Its negative surface charge (-27 mV) enables binding to positively-charged cell membranes, facilitating phagocytosis and intracellular dissolution over 2-3 days.^{[13]Specific Nickel Compounds as CarcinogensCosta M, Heck JD · 1982Open reference 13 ↓}

Nickel subsulfide (Ni3S2): most carcinogenic in NTP studies—readily endocytized, high solubility in biological fluids. Clear evidence of carcinogenic activity in F344/N rats at 0.6-1.2 mg/m3.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

Green nickel oxide (NiO): increased alveolar/bronchiolar adenoma or carcinoma in male rats at 0.62-2.5 mg NiO/m3 in 2-year NTP study.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

Nickel sulfate hexahydrate: soluble, rapidly cleared; non-neoplastic lung lesions at >=2.5 mg/m3 but no clear evidence of carcinogenicity.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓}

Particle clearance is the key determinant: impaired clearance leads to chronic Metal-Driven Inflammation and tumors. Insoluble compounds (NiS, NiO) are more potent than soluble forms (NiSO4, NiCl2) due to prolonged tissue retention.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Metallothionein vulnerability: nickel does not potently induce metallothionein (unlike cadmium), meaning the cell's natural chelation defense is not upregulated, potentially enhancing carcinogenic effects.^{[13]Specific Nickel Compounds as CarcinogensCosta M, Heck JD · 1982Open reference 13 ↓}

Nickel as a Metalloestrogen#

Nickel binds ERalpha (noncompetitively) and induces proliferation of ER+ breast cancer cells (2-5 fold at 10^-9 to 10^-6 M).^{[18]Role of Cadmium and Nickel in Estrogen Receptor Signaling and Breast Cancer: Metalloestrogens or Not?Aquino NB, Sevigny MB, Sabangan J et al. · 2012Open reference 18 ↓}

Induces cyclin D1, cyclin E, and cyclin B1 overexpression; causes aneuploidy in human fibroblasts.^{[18]Role of Cadmium and Nickel in Estrogen Receptor Signaling and Breast Cancer: Metalloestrogens or Not?Aquino NB, Sevigny MB, Sabangan J et al. · 2012Open reference 18 ↓}

This Metalloestrogens activity is relevant to nickel's connections with Endometriosis and breast cancer, though epidemiological evidence for nickel (Ni)-breast cancer is weaker than for Cadmium.^{[19]Impact of heavy metals on breast cancer (Review)Ali AS, Nazar ME, Mustafa RM et al. · 2024Open reference 19 ↓[20]Relationships Between Biological Heavy Metals and Breast Cancer: A Systematic Review and Meta-AnalysisLiu L, Chen J, Liu C et al. · 2022Open reference 20 ↓}

Nickel Allergy Overview#

Most frequent contact allergen worldwide: 8-19% of adults sensitized; 13-18% of females, 3-6% of males.^{[22]Nickel Allergy and Allergic Contact Dermatitis: A Clinical ReviewAhlström MG, Thyssen JP, Wennervaldt M et al. · 2019Open reference 22 ↓[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

See Nickel Allergy and Allergic Contact Dermatitis for immunology, regulation, and diagnosis. EU Nickel Directive limits: 0.2 ug/cm2/week for pierced body parts, 0.5 ug/cm2/week for prolonged contact.

Systemic Nickel Allergy Syndrome (SNAS)#

SNAS affects approximately 20% of nickel ACD patients and is the bridge between contact allergy and a vast array of systemic symptoms triggered by dietary nickel.^{[23]Systemic Nickel Allergy Syndrome: Nosologic Framework and Usefulness of Diet Regimen for DiagnosisBraga M, Quecchia C, Perotta C et al. · 2013Open reference 23 ↓[12]Systemic Nickel Allergy SyndromeDi Gioacchino M, Gatta A, Della Valle L et al. · 2018Open reference 12 ↓}

Diagnosis requires. Positive patch test to nickel. Symptom improvement on a low-nickel diet.

Positive oral nickel challenge (gold standard: double-blind placebo-controlled).^{[23]Systemic Nickel Allergy Syndrome: Nosologic Framework and Usefulness of Diet Regimen for DiagnosisBraga M, Quecchia C, Perotta C et al. · 2013Open reference 23 ↓[12]Systemic Nickel Allergy SyndromeDi Gioacchino M, Gatta A, Della Valle L et al. · 2018Open reference 12 ↓}

The BraMa-nickel (Ni) scoring system offers 94.4% sensitivity and 93.3% specificity for SNAS diagnosis, dramatically outperforming simple forbidden-food lists (51.1%/44.2%). The BraMa-nickel diet is nutritionally balanced at ~50 ug nickel/day.^{[23]Systemic Nickel Allergy Syndrome: Nosologic Framework and Usefulness of Diet Regimen for DiagnosisBraga M, Quecchia C, Perotta C et al. · 2013Open reference 23 ↓}

Symptoms of SNAS. Cutaneous (90% of patients): ACD flare-up, widespread eczema, urticaria, angioedema. Gastrointestinal (88%): meteorism, gastric acidity, abdominal colic, diarrhea, nausea, vomiting.

Meteorism is the most characteristic GI symptom after oral challenge. 73% report symptoms after a single nickel-rich meal.^{[23]Systemic Nickel Allergy Syndrome: Nosologic Framework and Usefulness of Diet Regimen for DiagnosisBraga M, Quecchia C, Perotta C et al. · 2013Open reference 23 ↓}

Immune mechanism: Both Th1 and Th2 pathways involved. IL-5 is the most significantly elevated cytokine within 24 hours of oral challenge. Nickel challenge induces CD4+CD45RO+ cell infiltration in intestinal mucosa with decreased CD8+ cells.^{[12]Systemic Nickel Allergy SyndromeDi Gioacchino M, Gatta A, Della Valle L et al. · 2018Open reference 12 ↓}

Lactose intolerance: 63-74% of SNAS patients have concomitant lactose intolerance, possibly due to nickel-induced brush border enzymatic impairment.^{[12]Systemic Nickel Allergy SyndromeDi Gioacchino M, Gatta A, Della Valle L et al. · 2018Open reference 12 ↓}

> Note: SNAS is not universally recognized in mainstream allergology. Some researchers argue that low-nickel diet benefits may overlap with low-FODMAP diet effects, and the two have not been adequately disentangled in clinical trials.

Hormonal Modulation of Nickel Allergy#

Nickel contact allergy varies with menstrual cycle phase: patch test reactivity is significantly lower during ovulation (peak estrogen) than during the progestinic phase (p<0.0001). False-negative patch tests may occur during ovulation.^{[26]Nickel contact allergy and menstrual cycleBonamonte D, Foti C, Antelmi AR et al. · 2005Open reference 26 ↓}

Oestradiol inhibits cell-mediated (type IV) hypersensitivity by acting on OKT8+ lymphocytes. The strong female predominance in SNAS studies may partly reflect hormonal cycling effects.^{[26]Nickel contact allergy and menstrual cycleBonamonte D, Foti C, Antelmi AR et al. · 2005Open reference 26 ↓}

Other SNAS Treatments#

Oral hyposensitization (NiOHT). Graduated oral nickel sulphate administration (0.1 ng to 0.1 mg over ~6 months) achieved 69.1% complete remission vs 17.9% in diet-alone controls (NNT = 1.95).^{[39]A Clinical Trial of Oral Hyposensitization in Systemic Allergy to NickelSchiavino D, Nucera E, Alonzi C et al. · 2006Open reference 39 ↓}

A refined protocol at 1.5 ug nickel (Ni)/week achieved 87% (20/23) sustained symptom freedom with food reintroduction. Mechanistically, NiOHT reduces nickel-induced IFN-gamma (55.3%), IL-13 (58.6%), and IL-5 (31.2%).^{[40]Oral Hyposensitization to Nickel Induces Clinical Improvement and a Decrease in TH1 and TH2 Cytokines in Patients with Systemic Nickel Allergy SyndromeMinelli M, Schiavino D, Musca F et al. · 2010Open reference 40 ↓}

Disulfiram chelation. Disulfiram (nickel-chelating agent) combined with low-nickel diet achieved 90.9% complete clearance of chronic vesicular hand eczema at 4 weeks (vs 10% placebo). Disulfiram metabolite diethyldithiocarbamate forces nickel excretion through urine, bile, and sweat.^{[41]Disulfiram and low nickel diet in the management of hand eczema: A clinical studySharma AD · 2006Open reference 41 ↓}

Nickel and Endometriosis#

A striking connection has emerged between nickel sensitivity and Endometriosis. 90.3% nickel (Ni) ACM prevalence in endometriosis patients with GI symptoms (nickel omPT positive). A 3-month low-nickel diet significantly improved all 15 gastrointestinal symptoms, all 7 extra-intestinal symptoms, and gynecological symptoms (dysmenorrhea, dyspareunia, pelvic pain).^{[25]Irritable Bowel Syndrome-Like Disorders in Endometriosis: Prevalence of Nickel Sensitivity and Effects of a Low-Nickel Diet. An Open-Label Pilot StudyBorghini R, Porpora MG, Casale R et al. · 2020Open reference 25 ↓}

Nickel may act as a metalloestrogen in endometriosis, binding estrogen receptors and promoting proliferation of estrogen-responsive tissue.^{[25]Irritable Bowel Syndrome-Like Disorders in Endometriosis: Prevalence of Nickel Sensitivity and Effects of a Low-Nickel Diet. An Open-Label Pilot StudyBorghini R, Porpora MG, Casale R et al. · 2020Open reference 25 ↓}

Peritoneal fluid nickel elevated 4:1 in a vegetarian endometriosis patient compared to controls (40.4 ug/L vs <LOD). The patient's vegetarian diet (high in tomatoes, nuts, legumes) was the likely exposure route.^{[42]Elevated Lead, Nickel, and Bismuth Levels in the Peritoneal Fluid of a Peritoneal Endometriosis Patient without Toxic Habits or Occupational Exposure following a Vegetarian DietLopez-Botella A, Gomez-Torres MJ, Sanchez R et al. · 2023Open reference 42 ↓}

Paradox: vegetarian diets frequently adopted for endometriosis management may increase nickel exposure through high consumption of plant-based, high-nickel foods.^{[42]Elevated Lead, Nickel, and Bismuth Levels in the Peritoneal Fluid of a Peritoneal Endometriosis Patient without Toxic Habits or Occupational Exposure following a Vegetarian DietLopez-Botella A, Gomez-Torres MJ, Sanchez R et al. · 2023Open reference 42 ↓}

Nickel Allergy and Overweight#

59.7% nickel allergy prevalence in overweight females (BMI >26), dramatically higher than 12.5% in the general female population (p<0.001).^{[43]High Prevalence of Nickel Allergy in an Overweight Female Population: A Pilot Observational AnalysisLusi EA, Di Ciommo VM, Patrissi T et al. · 2015Open reference 43 ↓}

A normocaloric low-nickel (Ni) diet reduced BMI by 4.2 (31.6 to 27.4), body fat by 5.1%, and waist circumference by 11.7 cm over 6 months in nickel-allergic overweight women.^{[43]High Prevalence of Nickel Allergy in an Overweight Female Population: A Pilot Observational AnalysisLusi EA, Di Ciommo VM, Patrissi T et al. · 2015Open reference 43 ↓}

Proposed mechanisms: nickel induces insulin-like actions, glycogenolysis, hyperglycemia; IL-17 from nickel-specific T cells is upregulated in obesity; estrogen deficiency at menopause may amplify nickel-mediated Th17 responses.^{[43]High Prevalence of Nickel Allergy in an Overweight Female Population: A Pilot Observational AnalysisLusi EA, Di Ciommo VM, Patrissi T et al. · 2015Open reference 43 ↓}

Nickel and Diabetes#

Meta-analysis of 20 studies (46,071 participants): urinary nickel shows a weak but positive association with diabetes risk (pooled SMD 0.16, p<0.01). Blood nickel does not show significant association.^{[44]Association between nickel exposure and diabetes risk: an updated meta-analysis of observational studiesLu H, Shi X, Han L et al. · 2024Open reference 44 ↓}

Proposed mechanisms: increased hepatic glycogenolysis, heightened pancreatic glucagon release, reduced glucose utilization, elevated inducible nitric oxide synthase.^{[44]Association between nickel exposure and diabetes risk: an updated meta-analysis of observational studiesLu H, Shi X, Han L et al. · 2024Open reference 44 ↓}

NHANES data links urinary nickel independently with metabolic dysfunction-associated steatotic liver disease, with insulin resistance mediating ~73.69% of the association.^{[45]Heavy Metals, Microbial Metallomics, and the US Obesity Epidemic: A Mechanistic Examination of a Population-Level Metabolic DisruptionKaren Pendergrass · 2026Open reference 45 ↓}

Nickel and Thyroid Function#

Dose-response relationship exists between blood nickel and thyroid hormone parameters (TSH, fT4, fT3, SPINA-GT, SPINA-GD).^{[46]Nickel as a potential disruptor of thyroid function: benchmark modelling of human dataMaric D, Baralic K, Javorac D et al. · 2023Open reference 46 ↓}

Males appear more susceptible: significant correlations found only in males for nickel (Ni) vs fT4 (p=0.039) and nickel vs SPINA-GT (p=0.013). At blood nickel levels of 1.36-60.9 ug/L, 78.68% of men may be at 10% higher risk of thyroid function alterations.^{[46]Nickel as a potential disruptor of thyroid function: benchmark modelling of human dataMaric D, Baralic K, Javorac D et al. · 2023Open reference 46 ↓}

Mechanism: oxidative stress (reducing glutathione, SOD activity) and perturbation of apoptosis-related proteins in thyroid tissue.^{[46]Nickel as a potential disruptor of thyroid function: benchmark modelling of human dataMaric D, Baralic K, Javorac D et al. · 2023Open reference 46 ↓}

Nickel and Chronic Fatigue / Fibromyalgia#

52% of 204 women with chronic fatigue and muscle pain had positive history of nickel contact dermatitis.^{[47]Nickel Allergy Is Found in a Majority of Women with Chronic Fatigue Syndrome and Muscle Pain - And May Be Triggered by Cigarette Smoke and Dietary Nickel IntakeRegland B, Zachrisson O, Stejskal V et al. · 2001Open reference 47 ↓}

Nickel allergy significantly impacted treatment response: only 16% of allergic patients were good responders to Staphylococcus vaccine therapy vs 37% of non-allergic patients (p<0.001).^{[47]Nickel Allergy Is Found in a Majority of Women with Chronic Fatigue Syndrome and Muscle Pain - And May Be Triggered by Cigarette Smoke and Dietary Nickel IntakeRegland B, Zachrisson O, Stejskal V et al. · 2001Open reference 47 ↓}

Among allergic smokers (cigarette smoke contains trace nickel), only 6% responded, suggesting synergistic worsening.^{[47]Nickel Allergy Is Found in a Majority of Women with Chronic Fatigue Syndrome and Muscle Pain - And May Be Triggered by Cigarette Smoke and Dietary Nickel IntakeRegland B, Zachrisson O, Stejskal V et al. · 2001Open reference 47 ↓} Case reports document improvement after low-nickel (Ni) diet and smoking cessation.^{[47]Nickel Allergy Is Found in a Majority of Women with Chronic Fatigue Syndrome and Muscle Pain - And May Be Triggered by Cigarette Smoke and Dietary Nickel IntakeRegland B, Zachrisson O, Stejskal V et al. · 2001Open reference 47 ↓}

Cardiac Toxicity#

Potentially associated with CVD and Metabolic Syndrome and Metal Exposure, but evidence is inconclusive at low doses in humans.^{[7]Cardio-Metabolic Effects of Nickel: A Narrative ReviewYucheng Liu, Xiaomin Luo, Yongde Peng et al. · 2025Open reference 7 ↓}

NHANES studies show associations between urinary nickel and various metabolic outcomes, but different studies using the same database reach contradictory conclusions.^{[7]Cardio-Metabolic Effects of Nickel: A Narrative ReviewYucheng Liu, Xiaomin Luo, Yongde Peng et al. · 2025Open reference 7 ↓}

Animal evidence is stronger and mechanistically detailed: nickel exposure (100 mg nickel (Ni)/L as NiSO4 in drinking water) significantly increases cardiac lipoperoxide and total lipid concentrations, serum cholesterol (+59%), LDH (+64%), and ALT (+30%)—markers of myocardial damage.^{[48]Toxic Mechanism of Nickel Exposure on Cardiac TissueNovelli ELB, Diniz YS, Almeida JA et al. · 2000Open reference 48 ↓}

The primary mechanism is superoxide radical accumulation: cardiac SOD is significantly decreased while catalase and GSH-Px are unchanged, indicating that the superoxide anion itself (not H2O2) is the primary damaging species.^{[48]Toxic Mechanism of Nickel Exposure on Cardiac TissueNovelli ELB, Diniz YS, Almeida JA et al. · 2000Open reference 48 ↓}

Vitamin E (alpha-tocopherol) reversed all biochemical parameters to near-control values in 15 days.^{[48]Toxic Mechanism of Nickel Exposure on Cardiac TissueNovelli ELB, Diniz YS, Almeida JA et al. · 2000Open reference 48 ↓}

Renal Toxicity#

Even at low doses, nickel has potential to cause significant kidney damage; exposure can progress from acute injury to acute tubulointerstitial nephritis to CKD and ESRD.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Heavy metal exposure (including nickel from soil contamination) associated with CKD progression to ESRD.^{[49]Prospective associations between environmental heavy metal exposure and renal outcomes in adults with chronic kidney diseaseTsai CC, Wu CL, Kor CT et al. · 2018Open reference 49 ↓}

Urinary metals including nickel studied in relation to kidney function biomarkers.^{[50]Association between urinary heavy metal/trace element concentrations and kidney function: a prospective studyXie S, Perrais M, Golshayan D et al. · 2025Open reference 50 ↓[51]Renal health and the environment: heavy metal nephrotoxicitySabath E, Robles-Osorio ML · 2012Open reference 51 ↓}

Neurotoxicity#

Chronic low-dose nickel causes anxiety, depression, and memory impairment in rats via hippocampal oxidative stress.^{[52]Effect of Chronic Administration of Nickel on Affective and Cognitive Behavior in Male and Female RatsLamtai M, Azirar S, Zghari O et al. · 2018Open reference 52 ↓}

Crosses BBB, accumulates in cerebral cortex; disrupts dopamine, serotonin, acetylcholine, GABA, and NMDA receptors. nickel(II) (Ni2+) can release dopamine and inhibit glutamate receptors.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Nickel inhibits Cob(I)alamin adenosyltransferase (vitamin B12 metabolism) with 50% loss at 100 uM nickel(II), potentially linking to neurological effects of B12 deficiency.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}

Alzheimer's Disease#

Nickel promotes Amyloid-Beta aggregation 5.7-fold and is the most abundant metal contaminant in recombinant Abeta40 (72.5 mmol/mol).^{[21]Benoit & Maier 2021 — Nickel Chelator Inhibits Amyloid-Beta AggregationBenoit, S.L., Bhatt et al. · 2021Open reference 21 ↓}

The nickel-specific chelator DMG inhibited aggregation 40-85%, suggesting nickel removal as a therapeutic target distinct from the well-studied copper and zinc chelation approaches (see Mis-metallation section above).

Included in reviews of dietary Heavy Metals and neurodegeneration.^{[53]Heavy metals in the diet: unraveling the molecular pathways linked to neurodegenerative disease riskGuevara-Ramirez P, Tamayo-Trujillo R, Cadena-Ullauri S et al. · 2024Open reference 53 ↓[54]Associations of Environmental Exposure to Arsenic, Manganese, Lead, and Cadmium with Alzheimer's Disease: A Review of Recent Evidence from Mechanistic StudiesGiasuddin Ahmed, Md. Shiblur Rahaman, Enrique Perez et al. · 2025Open reference 54 ↓}

Parkinson's Disease#

Nickel exposure is associated with increased risk of Parkinson's Disease, with the Gut Microbiome mediating part of the association.^{[55]Ji 2025 -- Nickel Exposure and Parkinson's Disease Risk: Gut Microbiome MediationWei Ji, Chen Yang, Zhigang Liu · 2025Open reference 55 ↓}

Nickel alters the abundance of specific bacterial taxa implicated in PD: pro-inflammatory Enterobacteriaceae are enriched while SCFA-producing commensals are depleted.^{[55]Ji 2025 -- Nickel Exposure and Parkinson's Disease Risk: Gut Microbiome MediationWei Ji, Chen Yang, Zhigang Liu · 2025Open reference 55 ↓}

Nickel-dependent bacterial enzymes (urease, hydrogenase) in gut pathogens contribute to dysbiosis and Ammonia-mediated epithelial damage, compounding iron-driven Ferroptosis in dopaminergic neurons.^{[56]Microbial Metallomics and Parkinson's Disease: A Unified Metal-Driven Framework Linking Ferroptosis, Dysbiosis, and alpha-Synuclein PathologyKaren Pendergrass · 2025Open reference 56 ↓}

The nickel-microbiome-neurodegeneration axis represents a specific instance of the broader metal dyshomeostasis framework for PD, where metal exposure reshapes gut ecology which in turn drives Neuroinflammation through the Gut-Brain Axis.^{[57]Pendergrass 2025 — From Dysbiosis to Dyshomeostasis: Why Parkinson's Requires a Metallomic–Microbiome LensKaren Pendergrass · 2025Open reference 57 ↓}

See Nickel Neurotoxicity for details.

Reproductive and Developmental Toxicity#

Maternal nickel exposure associated with congenital heart defects (aOR 1.326 for highest hair nickel (Ni) tertile).^{[58]Metal nickel exposure increase the risk of congenital heart defects occurrence in offspringZhang N, Chen W, Dong Y et al. · 2019Open reference 58 ↓} Pregnancy complications (GDM, HDCP) weaken placental barrier to nickel.^{[59]Pregnancy complications effect on the nickel content in maternal blood, placenta blood and umbilical cord blood during pregnancyDing R, Ruan Y, He X et al. · 2021Open reference 59 ↓}

Teratogenic in animal models: nickel carbonyl [nickel(CO)4] and nickel sulfide [Ni3S2] cause fetal malformations including cystic lung, exencephaly, anophthalmia, cleft palate, microphthalmia, hydrocephaly, exophthalmia, and skeletal defects.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Male reproductive toxicity: nickel disrupts sperm vitality and affects zinc-dependent metabolism essential for sperm quality; nickel-containing binding proteins act as DNA-binding proteins affecting spermatogenesis.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Nickel's role in male infertility is part of the broader heavy metals-infertility connection.^{[60]The Effects of Toxic Heavy Metals Lead, Cadmium and Copper on the Epidemiology of Male and Female InfertilityAliasgar Manouchehri, Sarima Shokri, Mohadesh Pirhadi et al. · 2022Open reference 60 ↓[61]Female Fertility and Environmental PollutionCanipari R, De Santis L, Cecconi S · 2020Open reference 61 ↓}

Pancreatic effects: acute and subchronic nickel exposure increases blood glucose and impairs insulin secretion—relevant to gestational diabetes risk.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Tampons contain nickel in 100% of tested samples (GM 80.1 ng/g), representing an underrecognized mucosal exposure route for reproductive-age women.^{[62]Tampons as a Source of Exposure to Metal(loid)sJenni A. Shearston, Kristen Upson, Milo Gordon et al. · 2024Open reference 62 ↓}

See Nickel and Reproductive/Developmental Toxicity for details.

Nickel in Baby Food and Children#

Children are a particularly vulnerable population due to immature detoxification systems and higher food intake relative to body weight.^{[63]Nickel Exposure from Food and Levels in Children's Blood and Tissues: Health ImplicationsDobrzyńska MM, Gajowik A, Jankowska-Steifer EA et al. · 2025Open reference 63 ↓}

91.8% of commercial baby foods contain nickel (up to 225.7 ug/kg); worst-case EDI may reach 497% of TDI in 2-year-olds.^{[64]Exposure to nickel through commercial premade baby foods: Is there any risk?Pereira AMPT, Silva LJG, Simoes BDF et al. · 2020Open reference 64 ↓}

Organic baby foods paradoxically have higher nickel: 100% detection, 54.7 ug/kg vs 35.8 ug/kg in non-organic (p=0.015).^{[64]Exposure to nickel through commercial premade baby foods: Is there any risk?Pereira AMPT, Silva LJG, Simoes BDF et al. · 2020Open reference 64 ↓}

In France, up to 98% of children aged 1-36 months exceed TDI under upper-bound assumptions; chocolate/cocoa accounts for 10% of mean daily intake in children.^{[63]Nickel Exposure from Food and Levels in Children's Blood and Tissues: Health ImplicationsDobrzyńska MM, Gajowik A, Jankowska-Steifer EA et al. · 2025Open reference 63 ↓}

Soy-based infant formula contains ~10x more nickel than cow's milk formula (0.45 vs 0.03 mg/L) and orders of magnitude more than human breast milk (0.005-0.016 mg/L).^{[65]Nickel as a Catalytic Driver of Necrotizing Enterocolitis: Dietary Nickel, Microbial Metallomics, and the Activation of Nickel-Dependent Virulence Pathways in the Preterm GutKaren Pendergrass · 2026Open reference 65 ↓}

Children near industrial areas have elevated urinary nickel correlated with markers of oxidative stress.^{[63]Nickel Exposure from Food and Levels in Children's Blood and Tissues: Health ImplicationsDobrzyńska MM, Gajowik A, Jankowska-Steifer EA et al. · 2025Open reference 63 ↓}

EFSA TDI: 13 ug/kg body weight/day (with a more protective 2.8 ug/kg b.w./day value previously in use). No maximum residue level for nickel in baby food exists.^{[64]Exposure to nickel through commercial premade baby foods: Is there any risk?Pereira AMPT, Silva LJG, Simoes BDF et al. · 2020Open reference 64 ↓}

German infant formula study and Italian baby food analyses confirm nickel as a ubiquitous contaminant.^{[66]The contribution of infant formula to the food survey-based dietary exposure of nine selected elementsHopfner T, Wollenberg M, Jager A et al. · 2025Open reference 66 ↓[67]Chemical characterization of baby food consumed in ItalyMeli MA, Desideri D, Sisti D et al. · 2024Open reference 67 ↓[68]Baby Food Jars as a Dietary Source of Essential (K, Na, Ca, Mg, Fe, Zn, Cu, Co, Mo, Mn) and Toxic Elements (Al, Cd, Pb, B, Ba, V, Sr, Li, Ni)Gonzalez-Suarez S, Paz-Montelongo S, Niebla-Canelo D et al. · 2022Open reference 68 ↓[69]Evaluation of Heavy Metals in Commercial Baby FoodsGaruba OD, Anglin JC, Good S et al. · 2024Open reference 69 ↓}

Nickel as a Catalytic Driver of NEC in Preterm Infants#

Dietary nickel from infant formula may be a critical but overlooked contributor to necrotizing enterocolitis (NEC) pathogenesis.^{[65]Nickel as a Catalytic Driver of Necrotizing Enterocolitis: Dietary Nickel, Microbial Metallomics, and the Activation of Nickel-Dependent Virulence Pathways in the Preterm GutKaren Pendergrass · 2026Open reference 65 ↓} Key NEC-associated pathogens (E. coli, Klebsiella, Enterobacter, Citrobacter, Ureaplasma) all rely on nickel-dependent enzymes: urease, hydrogenase, Glyoxalase I.

Excess dietary nickel creates a positive feedback loop: nickel (Ni)-fueled urease raises gut pH, favoring Proteobacteria over acid-producing commensals.

Human breast milk is naturally nickel-poor—potentially an evolved Nutritional Immunity (Metal Sequestration) mechanism starving nickel-dependent pathogens of their essential cofactor.^{[65]Nickel as a Catalytic Driver of Necrotizing Enterocolitis: Dietary Nickel, Microbial Metallomics, and the Activation of Nickel-Dependent Virulence Pathways in the Preterm GutKaren Pendergrass · 2026Open reference 65 ↓}

Proposed biomarkers: fecal urease activity, ammonia levels, and stool nickel content as early NEC risk indicators.^{[65]Nickel as a Catalytic Driver of Necrotizing Enterocolitis: Dietary Nickel, Microbial Metallomics, and the Activation of Nickel-Dependent Virulence Pathways in the Preterm GutKaren Pendergrass · 2026Open reference 65 ↓}

Reference Dietary Data#

Danish average diet: ~150 ug/day; roots/vegetables contribute 43.2% of intake.^{[10]Nickel Content of Food and Estimation of Dietary IntakeFlyvholm MA, Nielsen GD, Andersen A · 1984Open reference 10 ↓}

Cocoa has the highest nickel concentration of any common food: 3.0-12 ug/g,^{[10]Nickel Content of Food and Estimation of Dietary IntakeFlyvholm MA, Nielsen GD, Andersen A · 1984Open reference 10 ↓} up to 17.1 mg/kg.^{[63]Nickel Exposure from Food and Levels in Children's Blood and Tissues: Health ImplicationsDobrzyńska MM, Gajowik A, Jankowska-Steifer EA et al. · 2025Open reference 63 ↓}

Key Ni-Enzymes#

Urease: acid neutralization + nitrogen source. Essential for Helicobacter pylori, Staphylococcus aureus, Proteus mirabilis, Cryptococcus neoformans, and many others. Hydrogenase ([NiFe]): H2 oxidation for energy.

Critical for H. pylori (CagA translocation, CO2 fixation), Salmonella enterica serovar Typhimurium, Campylobacter jejuni.

Glyoxalase I I (GloI): methylglyoxal detoxification. Drug target in Leishmania donovani. E. coli GlxI specifically requires nickel(II) (Ni2+).^{[65]Nickel as a Catalytic Driver of Necrotizing Enterocolitis: Dietary Nickel, Microbial Metallomics, and the Activation of Nickel-Dependent Virulence Pathways in the Preterm GutKaren Pendergrass · 2026Open reference 65 ↓}

Acireductone dioxygenase (ARD): methionine salvage. Found in all pathogenic gamma-proteobacteriaceae. nickel-SOD: rare; oxidative stress defense in Streptomyces.^{[14]Role of Nickel in Microbial PathogenesisRobert J. Maier, Stéphane L. Benoit · 2019Open reference 14 ↓}

Nickel, Biofilm, and Antibiotic Co-Selection#

A particularly concerning aspect of nickel's ecological impact is its ability to co-select for antibiotic resistance—a phenomenon where nickel exposure simultaneously drives resistance to clinical antibiotics through shared genetic or regulatory mechanisms.^{[73]Baker-Austin 2006 — Co-selection of Antibiotic and Metal ResistanceBaker-Austin C, Wright MS, Stepanauskas R et al. · 2006Open reference 73 ↓}

Sub-inhibitory concentrations of nickel (62.5-250 ug/mL) induce antibiotic resistance in S. aureus, while high concentrations (500-1000 ug/mL) paradoxically increase antibiotic sensitivity. Bacteria adapted to moderate nickel (250 ug/mL) show the highest adhesion, highest biofilm formation, and greatest resistance to five tested antibiotics.^{[74]Bacterial Exposure to Nickel: Influence on Adhesion and Biofilm Formation on Orthodontic Archwires and Sensitivity to Antimicrobial AgentsPavlic A, Begic G, Tota M et al. · 2021Open reference 74 ↓}

This non-linear dose-response means that low-level chronic nickel exposure—the range most likely encountered from diet and consumer products—is the most dangerous for resistance selection.

Nickel released from orthodontic NiTi archwires (up to 40 ug/day) may create precisely these sub-inhibitory concentrations in the oral cavity.^{[74]Bacterial Exposure to Nickel: Influence on Adhesion and Biofilm Formation on Orthodontic Archwires and Sensitivity to Antimicrobial AgentsPavlic A, Begic G, Tota M et al. · 2021Open reference 74 ↓}

In agricultural soils, long-term nickel contamination increased the diversity and abundance of 149 unique antibiotic resistance genes spanning virtually every clinically relevant class (multidrug, beta-lactam, sulfonamides, tetracyclines, vancomycin).^{[75]Hu 2016 — Nickel Contamination and Antibiotic Resistance in SoilsHu HW, Wang JT, Li J et al. · 2016Open reference 75 ↓}

The integrase gene intI1 was the most connected node in resistance gene networks, mediating horizontal gene transfer from nickel-resistant organisms to other bacteria.^{[75]Hu 2016 — Nickel Contamination and Antibiotic Resistance in SoilsHu HW, Wang JT, Li J et al. · 2016Open reference 75 ↓}

Three distinct molecular mechanisms underlie co-selection: (1) co-resistance (physical linkage of metal and antibiotic resistance genes on the same plasmid or transposon), (2) cross-resistance (shared efflux pumps that expel both metals and antibiotics), and (3) co-regulatory mechanisms (shared transcriptional responses).^{[73]Baker-Austin 2006 — Co-selection of Antibiotic and Metal ResistanceBaker-Austin C, Wright MS, Stepanauskas R et al. · 2006Open reference 73 ↓}

Unlike antibiotics, metals are not degradable and represent a permanent selection pressure in contaminated environments.^{[73]Baker-Austin 2006 — Co-selection of Antibiotic and Metal ResistanceBaker-Austin C, Wright MS, Stepanauskas R et al. · 2006Open reference 73 ↓}

Nickel and the Gut Microbiome#

Heavy metals including nickel selectively eliminate beneficial SCFA-producing bacteria (Roseburia, Faecalibacterium prausnitzii, Bifidobacterium) while enriching metal-tolerant pathogenic species.^{[45]Heavy Metals, Microbial Metallomics, and the US Obesity Epidemic: A Mechanistic Examination of a Population-Level Metabolic DisruptionKaren Pendergrass · 2026Open reference 45 ↓[76]Influence of Toxic Metal Exposure on the Gut Microbiota (Review)Federica Giambo, Sebastiano Italia, Michele Teodoro et al. · 2021Open reference 76 ↓}

Nickel exposure causes a disturbed Firmicutes-to-Bacteroidetes ratio, decreased Bifidobacterium and Lactobacillus, mirroring the dysbiosis patterns seen across SNAS, obesity, and neurodegeneration.^{[77]The influence of nickel on intestinal microbiota disturbancesSwierc J, Drzymala S, Wozniak D et al. · 2022Open reference 77 ↓}

Nickel disrupts gut barrier integrity by affecting tight junction proteins; mechanisms parallel those documented for other heavy metals.^{[78]Effects of Heavy Metals on Gut Barrier Integrity and Gut MicrobiotaSweta Ghosh, Syam P. Nukavarpu, Venkatakrishna Rao Jala · 2024Open reference 78 ↓}

Probiotic metal detoxification: in an RCT of 152 occupational workers, probiotic yogurt containing Pediococcus acidilactici GR-1 reduced blood nickel by 38.34% (from 4.855 to 2.994 ug/L, p<0.0001) after 12 weeks, while enriching Blautia species and increasing fecal SCFA production.^{[79]Feng 2022 — Human supplementation with Pediococcus acidilactici GR-1 decreases heavy metal levels through modifying the gut microbiota and metabolomeFeng P, Yang J, Zhao S et al. · 2022Open reference 79 ↓}

This is the first human RCT demonstrating probiotic-mediated reduction of blood nickel levels.

Additional probiotic strategies for metal detoxification reviewed in.^{[80]Gut Microbiota: A Target for Heavy Metal Toxicity and a Probiotic Protective StrategyHui Duan, Leilei Yu, Fengwei Tian et al. · 2020Open reference 80 ↓[81]Potential Application of Living Microorganisms in the Detoxification of Heavy MetalsRunqiu Chen, Huaijun Tu, Tingtao Chen · 2022Open reference 81 ↓[82]Heavy Metal-Gut Microbiota Interactions: Probiotics Modulation and Biosensors DetectionLiliana Anchidin-Norocel, Oana C. Iatcu, Andrei Lobiuc et al. · 2025Open reference 82 ↓}

See Gut-Metal-Microbiome Interactions for the broader context.

Multiple Sclerosis#

In a case-control study (52 MS patients vs. 41 controls), urinary nickel was significantly elevated in MS patients and emerged as a significant risk factor (OR 1.47).^{[83]Effect of heavy metals and sialic acid in multiple sclerosisServin Yesil Günal, Hikmet Saçmacı, Şerife Saçmacı et al. · 2018Open reference 83 ↓}

Sialic acid, which binds toxic metals like nickel with high affinity, was dramatically elevated (OR 14.23), suggesting ongoing metal-induced tissue damage.^{[83]Effect of heavy metals and sialic acid in multiple sclerosisServin Yesil Günal, Hikmet Saçmacı, Şerife Saçmacı et al. · 2018Open reference 83 ↓}

Iron was protective (OR 0.52), consistent with lower iron (Fe) levels in MS patients and the nutritional immunity interpretation where low serum iron may reflect host defense rather than deficiency.^{[83]Effect of heavy metals and sialic acid in multiple sclerosisServin Yesil Günal, Hikmet Saçmacı, Şerife Saçmacı et al. · 2018Open reference 83 ↓}

Poor bowel habits increased MS risk 4.76-fold, supporting the Gut-Brain Axis involvement in metal-mediated MS pathology.^{[83]Effect of heavy metals and sialic acid in multiple sclerosisServin Yesil Günal, Hikmet Saçmacı, Şerife Saçmacı et al. · 2018Open reference 83 ↓}

ASD and Neurodevelopment#

Metal profiles (including nickel) are studied in ASD; trace metal imbalance is proposed as a primary pathology.^{[91]Metal Profiles in Autism Spectrum Disorders: A Crosstalk between Toxic and Essential MetalsBlazewicz A, Grabrucker AM · 2023Open reference 91 ↓}

Metal dyshomeostasis drives overlapping gut pathologies in ASD (intestinal barrier dysfunction, dysbiosis, inflammation)—nickel is notably absent from focused reviews but its gut effects parallel those of studied metals.^{[92]Metal Dyshomeostasis as a Driver of Gut Pathology in Autism Spectrum DisordersO'Grady K, Grabrucker AM · 2025Open reference 92 ↓}

Environmental and Regulatory Context#

EU Drinking Water Directive sets nickel limit at 20 ug/L.^{[94]Directive (EU) 2020/2184 on the Quality of Water Intended for Human Consumption (Recast)European Parliament, Council of the European Union · 2020Open reference 94 ↓} EFSA TDI: 13 ug/kg b.w./day (2020); previous value 2.8 ug/kg b.w./day. No maximum residue level for nickel in baby food.^{[64]Exposure to nickel through commercial premade baby foods: Is there any risk?Pereira AMPT, Silva LJG, Simoes BDF et al. · 2020Open reference 64 ↓}

Soil concentrations: background 3-1000 ppm; near nickel-producing industries, soils can reach 9,000 ppm.^{[8]Cameron 2011 — Nickel Genotoxicity and CarcinogenicityCameron KS, Buchner V, Tchounwou PB · 2011Open reference 8 ↓} Intensive urea-fertilizer regions show 35-85 mg/kg vs. background of 20-30 mg/kg.^{[95]Heavy Metals in Fertilizers: A Historical Analysis of Contamination Trends (1960-2025)Karen Pendergrass · 2026Open reference 95 ↓}

Water: rivers typically 0.3 ppb; seawater 0.5-2 ppb; drinking water <10 ug/L contributes 7.5-15.0 ug daily intake.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓}

Nickel contamination documented in fruit juices,^{[96]Evaluation of Heavy Metals Content in the Canned/Packed Fruit Juices from Local and Imported Origin in Lahore, PakistanNazeefa Fatima, Munazza Khan, Muhammad Shuaib Kabeer · 2020Open reference 96 ↓[97]Trace Metals and Contaminants in Commercial Fruit Juices Sold in South Eastern States, NigeriaOnyeneto T.C., Nwachukwu I.N., Nwogwugwu N.U. · 2015Open reference 97 ↓[98]Nutritional and Physio Chemical Analysis of Commercial Apple Juices and Natural Apple Juices Available in PakistanZahid Mehboob, Abid Ali, Faiza Azmat et al. · 2023Open reference 98 ↓} leafy vegetables,^{[99]Levels of Heavy Metals and Potential Human Health Risks via Consumption of Leafy Vegetables Purchased in Popular Local Market in Lagos, NigeriaO. O. Agboola, S. Oyedeji, T. A. Olawoyin et al. · 2023Open reference 99 ↓} and fish products.^{[100]Evaluation of the Risk from Potentially Toxic Elements (PTEs) in Italy's Most Consumed Processed Fish ProductsUnknown - file inaccessible due to encodingOpen reference 100 ↓}

Stainless steel cookware can elevate nickel content in food during cooking.^{[1]Nickel; A Metal with Threats to Human Health, Focusing on Its Intoxication MechanismsRafati Rahimzadeh M, Rafati Rahimzadeh M, Kazemi S et al. · 2025Open reference 1 ↓} Phytoremediation: hyperaccumulator plants (Alyssum murale, Sebertia acuminata) accumulate >1000 mg nickel (Ni)/kg dry weight.^{[5]Genchi 2020 — Nickel: Human Health and Environmental ToxicologyGenchi G, Carocci A, Lauria G et al. · 2020Open reference 5 ↓}