role of zinc in wound healing, The

Advances in Wound Care,  Apr 1999  by Andrews, Marti,  Gallagher-Allred, Charlette

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Abstract

Zinc deficiency has been associated with delayed wound healing. Because zinc deficiency may be common in the United States, foods rich in zinc, as well as all other essential nutrients, should be promoted in the diet of patients who are malnourished or at risk for malnutrition.

ADV WOUND CARE 1999;12:137-8

ZINC IS A TRACE MINERAL THAT IS A COMponent of many enzymes, including DNA and RNA polymerases, and it is required for protein synthesis, DNA synthesis, mitosis, and cell proliferation. Approximately 300 enzymes need zinc for proper functioning. Many of these zinc-dependent processes are required for wound healing, such as collagen synthesis and cell division. Consequently, zinc is an essential nutrient for normal wound healing.1

Although zinc deficiencies are most prevalent in areas in which the population subsists on cereal protein, there is considerable evidence that zinc deficiencies are widespread throughout the world. The first documented deficiencies in the U.S. were found in a group of children from Denver, Co.2 These children exhibited suboptimal growth, low hair zinc levels, poor appetite, and impaired taste acuity. More recently, studies by Prasad et al have shown that zinc deficiency in healthy, well-educated, free-living, elderly people in the United States may be fairly common.3 In a study of 118 subjects, Prasad found 36 (30.5%) had deficient zinc levels. Thus, the risk of zinc deficiency may pose a problem for a substantial segment of the U.S. population. Zinc deficiency symptoms in children include growth retardation, delayed sexual maturation, alopecia, skin lesions, impaired wound healing, immune deficiencies, night blindness, and impaired taste. A zinc deficiency in adults is frequently manifested as impaired wound healing, immune deficiencies, photophobia, night blindness, a diminished or abnormal sense of taste and smell, a susceptibility to respiratory infections, and decreased libido.

Zinc's RDA Established

Recommended dietary allowances (RDAs) for zinc were established in 1974 as a result of multiple reports of severe zinc deficiencies in patients receiving total parenteral nutrition (TPN) without zinc for extended periods of time. The severity of these deficiencies led to the establishment of RDAs for zinc, as well as the regular inclusion of zinc into TPN formulas. The current RDA (1989) for zinc is 15 mg/day for adult males and 12 mg/day for adult females.4 It is lower for females due to their lower body weight. Food sources of zinc that can readily supply the RDA include oysters, shellfish, herring, liver, legumes, milk, and wheat bran. In this country, 80% of total dietary zinc comes from meat, fish, poultry, grains, and milk and milk products.5

Initial studies of the specific impact of zinc supplementation on wound healing were promising. An early study of young men with wounds caused by excision of pilonidal sinuses and low levels of plasma zinc revealed improved rates of reepithelialization as a result of increased zinc intake, suggesting dietary zinc was inadequate in these subjects.6 Similarly, the healing of chronic venous leg ulcers, with respect to serum zinc levels and to the therapy applied, was investigated in a double-blind trial of 27 patients.7 Thirteen patients were given zinc sulfate (600 mg/ day); 14 were given placebo. Ulcers in patients with a serum zinc level higher than 110 mcg/100mL, or after zinc sulfate therapy, healed faster than did ulcers in patients with low serum zinc levels. In patients with normal serum zinc levels, no significant difference in healing was observed in those receiving zinc sulfate and those given placebo.

The positive impact of zinc supplementation in these 2 studies has not been systematically replicated.8 This may be directly related to the difficulty in assessing zinc status in patients. Strong homeostatic control of zinc absorption and excretion can maintain a person in zinc balance even when intake is lower than that provided in a typical U.S. diet. Serum zinc levels in healthy adults range from 95 to 130 mcg/ 100mL. This range, combined with the fact that as much as 20% of total body zinc is found in the skin (mainly in the form of zinc metalloenzymes), contributes to the difficulty in assessing zinc status.9 Although quantifying zinc status is difficult in the clinical setting, diets of patients recovering from wounds or burns often are supplemented with zinc.lo

Optimal Zinc Status I.inc S Important

In patients with dietary zinc deficiency, zinc therapy is indicated for wound healing. In light of the many important roles of zinc in human health, and specifically the impact of zinc deficiency on delayed wound healing, optimal zinc status must be maintained in patients. The elderly may be particularly susceptible to zinc deficiencies, especially if they do not eat protein-containing foods such as meat, fish, poultry, and milk and milk products due to cost, inability to chew, or dislike of these foods. Clinical signs of zinc deficiency, including a seborrhea-like dryness and redness of the nasolabial fold and eyebrows, should be used in combination with dietary intake data when considering zinc therapy in this population.