|Classification and external resources|
Even though zinc is an essential requirement for a healthy body, excess zinc can be harmful, and cause zinc toxicity. Such toxicity levels have been seen to occur at ingestion of greater than 225 mg of Zinc. Excessive absorption of zinc can suppress copper and iron absorption. The free zinc ion in solution is highly toxic to bacteria, plants, invertebrates, and even vertebrate fish.
Nausea, vomiting, pain, cramps and diarrhea.
There is also a condition called the "zinc shakes" or "zinc chills" or metal fume fever that can be induced by the inhalation of freshly formed zinc oxide formed during the welding of galvanized materials.
High levels of intake by humans
Zinc has been used therapeutically at a dose of 150 mg/day for months and in some cases for years, and in one case at a dose of up to 2000 mg/day zinc for months. A decrease in copper levels and hematological changes have been reported; however, those changes were completely reversed with the cessation of zinc intake.
There is no evidence that ordinary western people would benefit of increased doses of zinc. However, zinc has been used as zinc gluconate and zinc acetate lozenges for treating the common cold and therefore the safety of usage at about 100 mg/day level is a relevant question. Thus, given that doses of over 150 mg/day for months to years has caused no permanent harm in many cases, a one week usage of about 100 mg/day of zinc in the form of lozenges would not be expected to cause serious or irreversible adverse health issues in most persons.
One study has shown zinc to be highly efficacious for curing warts; oral intake of zinc sulfate for two months at levels up to 600 mg/day was found to induce complete clearance of recalcitrant warts, with a success rate of 87%.
Mechanism of toxicity
As described by the Free Ion Activity Model (FIAM), even micromolar amounts of the free zinc ion kills some organisms. The free zinc ion is also a powerful Lewis acid up to the point of being corrosive. When ingested, metallic zinc is readily dissolved by the hydrochloric acid of the stomach, and thus gives the corrosive zinc chloride. For example, swallowing a post-1982 American one cent piece (97.5% zinc) can cause damage to the stomach lining due to the high solubility of the zinc ion in the acidic stomach.
Copper. There is evidence of induced copper deficiency at low intakes of 100–300 mg Zn/d. The USDA RDA is 15 mg Zn/d. Even lower levels, closer to the RDA, may interfere with the utilization of copper and iron or to adversely affect cholesterol.
Zinc toxicity may take months to resolve.
- Fosmire GJ (February 1990). "Zinc toxicity". Am. J. Clin. Nutr. 51 (2): 225–7. PMID 2407097.
- Rout, Gyana Ranjan; Das, Premananda (1 January 2003). "Effect of Metal Toxicity on Plant Growth and Metabolism: I. Zinc". Agronomie 23 (1): 3–11. doi:10.1051/agro:2002073.
- SMITH, SE; LARSON, EJ (April 1946). "Zinc toxicity in rats; antagonistic effects of copper and liver.". The Journal of biological chemistry 163: 29–38. PMID 21023625.
- Muyssen, Brita, T. A.; De Schamphelaere, Karel A. C.; Janssen, Colin R. (2006). "Mechanisms of chronic waterborne Zn toxicity in Daphnia magna". Aquatic Toxicology 77 (4): 393–401. doi:10.1016/j.aquatox.2006.01.006. PMID 16472524.
- Pettilä, V.; Takkunen, O.; Tukiainen, P. "Zinc chloride smoke inhalation: a rare cause of severe acute respiratory distress syndrome". Intensive Care Medicine 26 (2): 215–217. doi:10.1007/s001340050049.
- Pories WJ, et al. (1967) Acceleration of healing with zinc sulfate. Ann Surg 165:432-6
- Simkin PA (1976) Oral zinc sulphate in rheumatoid arthritis. Lancet 2:539-42
- Samman S, Roberts DC (1987) The effect of zinc supplements on plasma zinc and copper levels and the reported symptoms in healthy volunteers. Med J Aust 146:246-9
- Forman WB, et al. (1990) Zinc abuse--an unsuspected cause of sideroblastic anemia. West J Med 152:190-2
- Fiske DN, et al. (1994) Zinc-induced sideroblastic anemia: report of a case, review of the literature, and description of the hematologic syndrome. Am J Hematol. 46:147-50
- Hemilä H (2011) Zinc lozenges may shorten the duration of colds: a systematic review. Open Respir Med J 5:51-8 Refs with links: http://www.mv.helsinki.fi/home/hemila/Zn/TORMJ.htm
- Al-Gurairi FT, Al-Waiz M, Sharquie (2002) Oral zinc sulphate in the treatment of recalcitrant viral warts: randomized placebo-controlled clinical trial. Br J Dermatol. 2002 Mar;146(3):423-31
- Bothwell, Dawn N.; Mair, Eric A.; Cable, Benjamin B. (2003). "Chronic Ingestion of a Zinc-Based Penny". Pediatrics 111 (3): 689–691. doi:10.1542/peds.111.3.689. PMID 12612262.