A narrative review synthesizing the epidemiological and mechanistic evidence linking excessive zinc intake (above the 40 mg/day tolerable upper intake level) to obesity, type 2 diabetes mellitus, hypertension, and cardiovascular disease. Covers antioxidant enzyme dysregulation, dyslipidemia, insulin resistance, and leptin resistance as converging mechanisms.
Key numbers
- Zinc tolerable upper intake level: 40 mg/day for adults (p. 1).
- Zinc recommended dietary allowance: 11 mg/day for adult men; 8 mg/day for adult women (p. 1).
- Prediabetes risk: 3.24-fold higher risk of prediabetes in participants with higher serum zinc concentrations in a cross-sectional analysis (p. 4).
- Type 2 diabetes mellitus risk: 51% higher risk of T2DM with higher serum zinc (p. 4).
- Excess zinc mechanism on antioxidant enzymes: Cu/Zn SOD (superoxide dismutase 1) dysregulation; reduced glutathione peroxidase (GPX) and catalase (CAT) activity; impaired overall antioxidant capacity (p. 3).
- Cardiovascular mechanism: dyslipidemia (altered LDL-cholesterol and triglycerides), leptin resistance impairing satiety signaling, and direct vascular effects contributing to hypertension (p. 3-4).
- Zinc-copper antagonism: metallothionein induction by excess zinc sequesters copper in enterocytes, reducing copper absorption and producing secondary copper deficiency (p. 3).
- LOD/LOQ: not reported (review paper, no primary analytical measurements).
Methods (brief)
Narrative review. No systematic search protocol described. Primary data are from cited epidemiological studies and experimental models. Because this is a review paper, LOD/LOQ, certified reference material (CRM) use, and recovery data are not applicable.
Evidence fitness
Supports: characterization of mechanisms by which excess zinc disrupts cardiometabolic function (antioxidant enzyme dysregulation, dyslipidemia, insulin resistance, leptin resistance), and cross-sectional epidemiological associations between higher serum zinc and prediabetes or hypertension risk. The 3.24-fold prediabetes association and 51% T2DM association are cited from observational studies reviewed in the paper; primary study designs, sample sizes, and adjustment factors are not fully detailed in this review and require verification against the cited primary literature. Does not provide food concentration data, food-matrix measurements, or deficiency outcomes.
Limitations
Narrative (not systematic) review with no PRISMA protocol. Epidemiological estimates are from cross-sectional and observational studies, which cannot establish causation. The specific odds ratios and risk estimates for prediabetes and T2DM are derived from the reviewed primary literature and may reflect residual confounding (body mass index, dietary pattern, supplement use). The review focuses on excess, and does not substantively address deficiency outcomes.
Related evidence
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