National Institute of Environmental Health Sciences, Research Triangle Park,
NC 27707.
Lead, cadmium, and mercury are toxic metals that are not essential for
nutrition. However, the toxic effects of these metals may be mediated or
enhanced by interactions or deficiencies of nutritionally essential metals.
Lead competes with calcium, inhibiting the release of neurotransmitters, and
interferes with the regulation of cell metabolism by binding to
second-messenger calcium receptors, blocking calcium transport by calcium
channels and calcium-sodium ATP pumps, and by competing for calcium-binding
protein sites and uptake by mitochondria. Dietary deficiencies of calcium,
iron, and zinc enhance the effects of lead on cognitive and behavioral
development. Iron deficiency increases the gastrointestinal absorption of
cadmium, and cadmium competes with zinc for binding sites on metallothionein,
which is important in the storage and transport of zinc during development.
Selenium protects from mercury and methyl
mercury toxicity by preventing damage from free radicals or by forming
inactive selenium mercury complexes.
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