Zinc is an essential dietary nutrient. It is best to consume zinc from food as deficiencies are rare and supplements can often lead to an overdose. Zinc deficiencies and toxicities have few exclusive symptoms, but can sometimes lead to serious complications. No known benefits to a diet rich in zinc have been documented, but overall, it is important to have a diet full of variety and balance to ensure adequate intake of zinc and other essential nutrients.
Function
Zinc is a trace mineral with a role in more than 200 bodily enzymatic reactions, including carbohydrate metabolism, protein synthesis, protein catabolism, carbon dioxide transport and nucleic acid (DNA and RNA) synthesis. The highest concentrations of zinc are located in bones, muscles, hair, skin and nails.
Dosage
The upper level of zinc intake daily for adults is 40 mg. The medium intakes in the United States are 9 to 13 mg/day. Long-term intakes of 300 to 400 mg per day, often from excessive supplement use, can lead to copper deficiency, anemia and may impair immune function. A supplement is only necessary when the recommended intakes cannot be reached, and when consumed, the supplement dosage should not exceed the tolerable upper intake levels.
Deficiency
Due to its numerous roles in the body, deficiency symptoms of zinc are numerous. Signs of deficiency most commonly noted are impaired growth, alopecia (hair loss), diarrhea, delayed puberty, and eye and skin lesions. Deficiency is rare, but certain demographic groups are more susceptible, such as the elderly, people with HIV, pregnant women, people with alcoholism and diabetics.
Food Sources
Zinc is found in meat, eggs, seafood, whole grains, nuts and legumes. The foods highest in zinc are ground beef, containing 5.36 mg of zinc per 3.5 oz. serving, and wheat germ, which contains 3.22 mg of zinc per 2 tbsp. serving. Plant foods containing phytic acid, such as spinach, will bind with zinc and decrease its intestinal absorption. Limiting spinach consumption when consuming zinc-rich foods will improve absorption and decrease risk for deficiency.
Speculation
Zinc has been studied and used as a weapon against the common cold, macular degeneration (vision loss due to age), acne and immunity disorders. None of these claims has been proven completely accurate, but zinc's influence on immunity has shown the most progress in one area. Zinc supplements have proven to decrease mortality and respiratory illness in low-birth-weight infants. More research is needed to determine the full effect zinc may have on the immune system.
References
- "A Health Professional's Guide to Popular Dietary Supplements"; Allison Sarubin Frangakis and Cynthia Thomson; 2007
- "Minerals from Plant Foods: Strategies for Maximizing Nutrition"; Carol Meershaert; 2002
- Pediatrics (journal); "Zinc Supplementation in infants born small for gestational age reduces mortality: a prospective, randomized controlled trial; S. Sazawal"; 2001
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