A cluster of conditions — high blood pressure, impaired fasting glucose, insulin resistance, abdominal obesity (BMI ≥25), high triglycerides, low HDL-C — defined by the presence of ≥3 components. Emerging evidence links MetS to environmental nickel exposure, though findings remain inconclusive [1].
Evidence for Nickel-MetS Association
Occupational Studies
- Chinese nickel-exposed workers (n=35,104, Jinchuan): elevated age-adjusted prevalence of MetS components (hypertension 29.5%, abnormal lipid 27.5%, BMI ≥25 13.9%).
- Diabetes prevalence in nickel workers: 12.8% (vs. 11.6% national average).
- Higher in males than females across most MetS components.
Population Studies (NHANES)
- Eight studies used NHANES 2017-2018 data with different designs and reached contradictory conclusions — a central finding highlighting methodological challenges.
- Luo et al. 2024: inverted L-shaped dose-response with MetS; inflection at UNi 0.2141 μg/L. Effects strongest in males >40, less educated, smokers.
- Strongest correlations: high fasting glucose, reduced HDL-C, abdominal obesity, elevated blood pressure.
- No significant correlation between nickel and hyperlipidemia.
Dose-Response Complexity
- Multiple non-linear patterns observed: U-shaped, inverse U-shaped, and L-shaped curves depending on the outcome and study.
- Zhang et al.: plasma nickel was lower in T2DM patients vs. controls — suggesting nickel may be essential at low levels, complicating the dose-response picture.
- No animal model exists at UNi-equivalent doses <6.1 μg/L.
Proposed Mechanism
- oxidative stress is the primary proposed link: increased SOD, reduced catalase, elevated MDA.
- Nickel interactions with other metals (zinc, vanadium, chromium, copper) may modulate effects.
- MASLD (metabolic dysfunction-associated steatotic liver disease) also linked to serum nickel in sex-specific patterns.
Key Limitations
- All major human studies are cross-sectional — cannot establish causation.
- Studies use different clinical variables, inclusion criteria, and statistical methods on the same database.
- Biological plausibility mainly supported at high concentrations, not environmental levels.
- Nickel's potential essentiality confounds low-dose interpretation.
Connections
- nickel — the implicated metal
- oxidative stress — proposed mechanism
- Relates to metal carcinogenesis as a non-cancer endpoint of metal toxicity