Food Toxicology 2(2+0)

Lesson 17 : Toxicity of Nutrients

Minerals and Trace Elements

As regards the toxic effects of minerals and trace elements, the absolute level of intake is not the only circumstance involved with either acute or chronic toxicity. Toxic intake levels can vary considerably with individual circumstances. An element that is easily stored may accumulate in tissues over time, and therefore ingestion of a lower concentration may produce a toxic effect that would not occur in an individual without any prior exposure. Other circumstances that may influence the toxicity of a mineral or trace element include absorption and excretion factors, immobilization or storage of the toxic element (bone storage), and detoxification mechanisms.

1. Magnesium
   Excessive intake of magnesium salts can result in hypermagnesemia. Such patients have concomitant renal failure. Neuromuscular symptoms are common. Nonspecific effects of magnesium intoxication include nausea, vomiting, and cutaneous flushing. Depressed respiration and apnea due to paralysis of the voluntary musculature and cardiac arrest may occur.

2. Iron
   Iron overloads can be a serious problem for some individuals. The best-defined example of iron overload is hereditary hemochromatosis, an inherited disease. In hemochromatosis, iron is absorbed in excess of what is needed, leading to accumulation of iron and saturation of transferrin. Subsequent iron loading results in clinical complications of diabetes mellitus, endocrine abnormalities, cardiomyopathy, arthritis, liver cirrhosis, and hepatic cancer.

3. Zinc
   Long-term intakes of 6 to 20 times the RDA can produce overt zinc toxicity. Symptoms of zinc toxicity include impaired immune response, reduction in high density lipoprotein (HDL) cholesterol levels and induced copper deficiency (anemia). Acute effects of high zinc intake are vomiting, epigastric pain, fatigue, and lethargy. Particular concerns have been expressed regarding the popularity of zinc gluconate lozenges for the common cold. A lozenge contains 13 mg of zinc, which if taken every 2 h can approach toxic doses.

4. Copper
   Once the capacity of the liver to bind copper is exceeded, toxicity may occur. GI distress has been seen with copper intakes of 5 mg/d. Weakness, listlessness, and anorexia are early signs of copper toxicity, followed by hepatic necrosis, vascular collapse, coma, and death.

5. Selenium
   Long-term intakes of dietary selenium at 4 to 5 mg/kg of diet are sufficient to cause growth inhibition and result in tissue damage of the liver. Selenium toxicity in humans brings on symptoms of nausea, weakness, and diarrhea, and eventually hair loss, changes in nails, mottling of the teeth, and lesions of the skin and nervous system.