Zinc toxicity can be either acute or chronic. Acute zinc overdoses can start at 40 mg and cause intestinal distress, such as nausea, diarrhea, cramping and loss of appetite, according to the Linus Pauling Institute. Extreme overdoses of zinc -- above 150 mg -- have been associated with diminished immune function, reduced oxygen transport due to poor iron function and lowered HDL cholesterol, which is the "good" type of cholesterol. Tolerable upper intake levels (UL), are established for each age group, to prevent overdoses.
Proper Dosage For Adults
You need different amounts of zinc depending on gender. Adult women require 8 mg, but men need as much as 11 mg. If you are pregnant, you need 11 mg, which increases to 12 mg while breastfeeding. The major consequence of long-term excessive zinc intake is a copper deficiency. Total zinc intakes of 60 mg/day have been found to result in signs of copper deficiency, notes the Linus Pauling Institute. To prevent copper deficiency, The U.S. Food and Nutrition Board set the tolerable upper level of intake for adults at 40 mg/day, including dietary and supplemental zinc; however, children have different toxicity levels.
Tolerable Upper Limit for Children
Until 6 months of age, the tolerable upper level of intake for an infant is 4 mg of zinc. Between 7 and 12 months, the UL is 5 mg, while from 1 to 3 years, the UL is 7 mg. Children ages 4 to 8 years have a UL of 12 mg, while for children ages 9 to 13, the UL is 23 mg. Adolescents ages 14 to 18 have a UL of 34 mg to avoid adverse health effects.
Functions
Zinc is an important trace element that plays a role in growth and development. It can be broken down into three different types of functions: catalytic, structural or regulatory. About 100 different enzymes depend on zinc for its ability to catalyze, or speed up chemical reactions. Zinc is also involved in the structure of proteins and cell membranes. Without zinc, cells are more prone to oxidative damage, resulting in chronic illness. Lastly, zinc regulates gene expression and influences the release of certain hormones.
Food Sources
Overdosing from dietary zinc is not common, since the UL is relatively high. Animal foods are naturally high in zinc. Oysters in particular are very high; six medium oysters have more than 75 mg of zinc, so you should avoid eating too many oysters at once. A 3 oz. serving of beef shank provides 8.9 mg, 3 oz. of Alaska king crab has 6.5 mg, one roasted chicken leg contains about 2.7 mg and 3 oz. of pork provides 4.2 mg. Fortified breakfast cereal has nearly 1 mg per 1-cup serving. Some plant foods are naturally high in zinc as well. A 1/2 cup serving of baked beans contains 1.7 mg, 1 oz. of cashews has 1.6 mg and 1/2 cup of cooked peas provides .8 mg.
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