The Potential Role of Zinc Supplementation on Pressure Injury Healing in Older Adults

A Review of the Literature

Melissa Heintschel, MS, RD, LD; Roschelle Heuberger, PhD, RD

Disclosures

Wounds. 2017;29(2):56-61. 

In This Article

Zinc

Zinc plays a significant role in several biochemical and physiological functions.[13] These functions include but are not limited to: control of gene transcription and translational regulation vital for deoxyribonucleic acid repair, transcriptional regulation, and protein metabolism, as well as catalytic enzyme activity for many biological processes in intermediary metabolism and insulin signaling.[14–16] Zinc also plays a role in immunocompetence. Without adequate Zn availability, T-helper and B-helper cells fail to reach maturation, subsequently leading to lymphopenia along with impaired natural killer cell and phagocytic cell function.[14] Suboptimal Zn levels impair secretion of cytokines, regulation of interferon gamma, tumor necrosis factor, and production of interleukin-2;[14] these are vital for immune response.[14] Most relevant to this literature review is the need for Zn for normal functioning of anabolic processes for growth, tissue maintenance, and wound healing.[17]

The recommended dietary allowance (RDA) for Zn in adults (≥ 19 years) is 8 mg/d to 11 mg/d, and the American Society for Parenteral and Enteral Nutrition has suggested that nutritional needs are further increased for critically ill patients.[17,18] Dietary sources of Zn can be found in meat products, such as oysters, organ meats, fish, and beef.[15] In contrast, some plant-based foods may be good sources of Zn, but are less bioavailable due to the presence of phytate, iron, and fiber, which inhibit Zn absorption.[17] The third National Health and Nutrition Examination Survey found 57.5% of the advanced age population (≥ 71 years) consumed inadequate levels of Zn in their diet, and advanced age contributes to decreased dietary Zn intake below recommended guidelines (≤ 77% RDA).[5] Additionally, Zn is primarily transported from the small intestine, and intestinal absorption decreases with aging.[13] Consequently, it is difficult to assess the adequacy of dietary Zn levels in older adults due to reduced intakes and absorption. Surrogate measures (eg, dietary assessment of a patient's overall nutritional status) should be evaluated when considering a possible Zn deficiency. These assessments include inadequate intake, reduced absorption, increased losses, or increased nutrient needs.[17]

With respect to intracellular concentrations, Zn homeostasis is maintained via multiple feedback controls to preserve tight regulation and adequate levels. There is no site for storage; Zn is recycled through an internal reservoir or "pool."[17,19] A further obstacle in evaluating Zn status is lack of a reliable biomarker.[13] Although plasma Zn concentrations are the most widely used biomarker to assess Zn status, it is an insensitive marker for deficiency.[20] Many factors can result in false positive hypozincemia, such as hypoalbuminemia, that have an impact on the validity of these test results.[17,20] The normal range for plasma Zn level range is 12 μmol/L to 18 μmol/L (78 μg/dL–118 μg/dL).[12] It can also be measured by urinary Zn, but has little validity due to several factors affecting its loss in urine aside from Zn status.[20] The pancreas, prostate, and mammary glands have unique Zn requirements for metabolic processes, but measuring Zn from tissue biopsies is not used in practice.[21] Several other biochemical markers have been considered but have not been found to be useful indicators of Zn status.[17] A potential biomarker that may be useful in future research is the copper to zinc ratio (CZr), which has been a suggested biomarker for physical and functional decline associated with aging. Though the role of this marker is to predict mortality rather than evaluate Zn status, it may be useful in determining associations with immobility and risk of development in PIs in the aged population.[22] Future research is needed to validate the use of this measure. As a result, it is difficult to assess Zn status from biochemical markers. Despite being unable to measure the efficiency of Zn absorption and imprecise measures of Zn status using plasma Zn, the International Zinc Nutrition Consultative Group currently recommends monitoring Zn status by assessing plasma Zn concentration and dietary intakes, though alternative indicators are under investigation.[23]

Due to risk of poor dietary intakes and decreased efficiency in Zn absorption with aging, monitoring Zn status for older patients with PIs should be part of clinical practice for optimal wound healing outcomes. In the event of deficit, nutritional interventions should be instituted. These nutritional interventions include standard ONS, specialty ONS formulas, Zn sulfate, and potentially L-carnosine (CAR) and its Zn complex, polaprezinc (PLZ).

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