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 [liu 2025 cardiometabolic nickel].
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
1. All major human studies are cross-sectional — cannot establish causation.
2. Studies use different clinical variables, inclusion criteria, and statistical methods on the same database.
3. Biological plausibility mainly supported at high concentrations, not environmental levels.
4. 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