Zinc Supplementation: Yea or Nay?

Advances in Skin & Wound Care, Sep/Oct 2003 by Collins, Nancy

Q: Should I include zinc supplements as part of the standard treatment protocol for patients with pressure ulcers? If so, what type of zinc is best and in what amount?

A: There is no clear consensus in the scientific community about zinc supplementation to improve wound healing. This is likely due to the difficulty in conducting randomized controlled studies that singularly and definitively identify zinc as the significant factor. Most of the evidence on zinc is based on anecdotal experience, observation, or logical reasoning. Therefore, each facility or wound care center must choose its own policy based on the available evidence and what is known about zinc. Whatever the decision, it is important to have a clear policy that is followed consistently and an understanding of the rationale on which the policy is based.

Functions of Zinc

Zinc is an essential mineral and is found as a component of almost every living cell in the body. It stimulates the activity of approximately 100 enzymes, including about 2 dozen known zinc metalloenzymes.1 Zinc is associated with wound healing because of its role in collagen synthesis and cell proliferation. All proliferating cells, including inflammatory cells, epithelial cells, and fibroblasts, require zinc.2 In addition, zinc plays a central role in the immune system and is needed for antibody production and proper activity of lymphocytes. Zinc also functions as an antioxidant and a membrane stabilizer and has many roles in basic cellular function, such DNA replication, RNA transcription, and cell division. Zinc also plays a role in taste acuity and sense of smell; interacts with platelets for blood clotting; and participates in the synthesis, storage, and release of insulin.3

Requirements

Most clinicians refer to the National Academy of Sciences-National Research Council (NAS-NRC) Recommended Dietary Allowances (RDAs) for specific recommendations of zinc intake. The NAS-NRC updated its recommendations for zinc in 2001 as part of the Dietary Reference Intakes (DRI) program. The DRI provides RDAs and upper limits (UL) that are age- and gender-specific. The UL is the maximum level of daily intake that is not likely to pose a risk of adverse effects. Table 1 outlines the RDAs for zinc. For adults, the RDA is 11 mg/day for men and 8 mg/day for women.4 Keep in mind that RDAs are recommendations for healthy people and do not address illness or disease states.

The Agency for Health Care Policy and Research (AHCPR; now the Agency for Healthcare Research and Quality) clinical practice guideline for the treatment of pressure ulcers does not specifically recommend zinc. However, it does recommend a daily high-potency vitamin and mineral supplement for all patients suspected of having a vitamin deficiency.5

Zinc Deficiency

Zinc supplementation in a patient with a zinc deficiency is different than zinc supplementation in all patients with wounds. The argument that zinc deficiency impedes wound healing is much stronger than the argument that extra zinc will improve wound healing. This important distinction, however, is often overlooked in discussions of zinc.

Assessing zinc status is challenging, making it difficult to determine which patients are deficient. Plasma and serum zinc levels are the most widely used methods of zinc assessment, but they are not necessarily reflective of true zinc status.6 Zinc is primarily bound to albumin; deficiencies in albumin have a significant impact on zinc levels. Zinc's main functions are intracellular; therefore, serum and plasma levels do not reflect total body stores.6

Although several other ways to assess zinc status exist (eg, hair zinc), there is no practical, accurate, cost-effective, and generally accepted method to determine zinc status. Practitioners should draw logical conclusions from a patient's diet history, physical assessment, and other laboratory data. Physical signs of zinc deficiency include loss of appetite, diarrhea, hair loss, sexual impotence, delayed wound healing, skin abnormalities (eg, atopic dermatitis, psoriasis), taste abnormalities, white spots on the fingernails, and mental lethargy or depression.7,8 Vegetarians and alcoholics tend to have low zinc status and this should be noted when taking a patient's history. If a patient is eating poorly, has a history of involuntary weight loss, a non-healing wound despite optimal local care, depleted visceral proteins, and a malabsorptive disease, a zinc deficiency should be suspected. A thorough assessment and clinical judgment are perhaps the best tools for assessing zinc status.

Sources of Zinc

Oysters are the richest source of zinc. Other foods high in zinc include red meat, poultry, shellfish, fortified breakfast cereals, whole grains, legumes, cooked greens, brewer's yeast, and nuts. Table 2 shows the zinc content of selected foods.

The daily mean intake from an adult self-selected diet in the United States ranges from 8.6 to 14 mg zinc.9 When evaluating a patient's zinc intake, keep in mind that, in addition to food, many patients receive a daily multivitamin, which typically contains 15 mg of zinc. These same patients may also receive medical nutrition supplements such as Ensure (Ross Products, Columbus, OH) or Boost (Mead Johnson, Evansvillc, IN). One 8-ounce can of Ensure contains 3.8 mg of zinc, and 1 can of Boost contains 4.5 mg of zinc. If these supplements are ordered 3 times per day, which is typical, Ensure would provide 11.4 mg/day of zinc and Boost would provide 13.5 mg/day. Factoring in the multivitamin, the patient's total zinc intake would then be approximately 27 mg/day with 100% consumption, or about 2 ½ to 3 times the KDA.