The mineral zinc is required by your body in trace amounts. It performs a variety of normal biochemical functions, including maintaining your immune system, synthesizing proteins and permitting catalytic activity in enzymes, and it supports proper growth and development. You can get your recommended daily servings of zinc from a well-balanced diet, but too much zinc can have adverse effects in the form of acute or chronic toxicity.
Daily Intake and Upper Limit
The daily recommended intake for zinc in adult females is 8 mg; for males it is 11 mg. Pregnant and lactating adult females require a higher daily intake of 11 to 12 mg. The tolerable upper intake level of zinc for all adults is 40 mg/day; this includes dietary or supplemental forms of the mineral. Acute effects of excess zinc include nausea, vomiting, abdominal cramps, diarrhea and headaches. Chronic effects of excess zinc include reduced immune functions, copper deficiency and altered iron absorption.
Zinc Poisoning
Single episodes of excess zinc in your diet may not produce adverse effects unless it has been ingested from poisoned substances like food or beverages in contaminated galvanized containers. In this event, a toxic dose of 225 to 450 mg may induce vomiting, gastrointestinal distress, convulsions and collapse. The occurrence of zinc poisoning is rare. Err on the side of caution by avoiding foods stored or prepared in galvanized containers and by consuming only the daily recommended amount of zinc from dietary sources. Additionally, your physician may prescribe high doses of zinc temporarily to treat medical conditions; but you should not exceed the safe upper limit dose of zinc without physician consultation.
Zinc Sources
A serving of cooked oysters yields 76.3 mg of zinc, which far exceeds the upper limit dose. Crab and lobster offer a lower zinc alternative with 3.4 to 6.5 mg per 3-oz. serving. Or, if you prefer meat from land animals, opt for beef, pork and chicken, which provide 2.5 to 8.9 mg per 3-oz. serving. The zinc from meats absorbs readily in your body, but plant-based foods with zinc absorb only in fractional amounts because of phytic compounds that inhibit full zinc absorption. Whole grain breads and cereals, beans and nuts are among the foods with zinc that may not absorb fully. These foods generally have less than 2 mg per serving size.
Additional Considerations
The Office of Dietary Supplements advises you get zinc from natural food sources to prevent excess consumption and adverse effects. Multivitamins generally contain zinc, and you should read the nutrition facts label to ensure you are not getting too much from the supplement. Consult your physician before taking supplements to ensure safety. Zinc may interact with medications including antibiotics and diuretics. Zinc generally decreases the effectiveness of antibiotics, and prolonged use of diuretics can cause you to lose excess zinc in your urine.
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