The treatment of burns, surgical and traumatic wounds, diabetic ulcers... pose a significant medical challenge. Successful wound repair requires a series of closely coordinated steps, including coagulation, inflammation, angiogenesis (formation of new vessels from a pre-existing network), the formation of new tissues and the remodelling of the extracellular matrix. How does zinc accelerate healing? Is it as effective orally as it is topically?
Does zinc aid in wound healing?
Summary
Published on July 2, 2024, by Maylis, Chemical Engineer — 5 min of reading
Themes:
Zinc, in brief.
Zinc is a crucial micronutrient, present in small amounts in the human body, less than 50 mg/kg. It is vital for the body's health due to its critical roles in growth and development, bone metabolism, the central nervous system, immune function, and wound healing, which is the focus of this article.
Zinc is a vital cofactor for the function of over 10% of proteins encoded by the human genome, representing no less than 3,000 proteins and enzymes. Zinc-dependent proteins play numerous indispensable roles within cells, such as transcriptional regulation, DNA repair, cell death, metabolic processing, regulation of the extracellular matrix (ECM), and antioxidant defence.
It should be noted : this trace element cannot be stored by the body. Therefore, to reap its benefits, regular consumption of zinc-rich foods is essential. The food richest in zinc is the oyster, but there are others such as offal, red meat, wholemeal bread and eggs. The vast majority of zinc present in the human body is stored in skeletal muscles (60%), but reserves are also present in the bones (30%), skin (5%), liver and other organs (2 to 3%).
Zinc is particularly important for the skin. The skin contains a relatively high zinc content (approximately 5% of the body content), primarily associated within the epidermis (50-70 μg/g of dry weight). Due to its abundance in the epidermis, it is observed that a slight zinc deficiency results in rough skin and an alteration in wound healing.
Studies dating back to 1970 and earlier have demonstrated the significance of zinc concentrations in wound healing in patients suffering from thermal injuries or exposed to surgical stress.
Oral zinc supplementation to accelerate wound healing.
From as early as the 1970s, the benefits of zinc supplementation have been reported in critically ill patients, severe burn victims, subcutaneous abscesses, minor surgery, and bedsores. Wound healing, inflammation, and immune response are intimately linked to each other. Over the years, it has been demonstrated that zinc is capable of modulating both innate and adaptive immune functions. Zinc alters immune responses in a multitude of ways, ranging from myeloid-derived cells and inflammatory signalling to lymphocyte differentiation and antibody production.
In this regard, certain wound care protocols recommend a daily supplementation of elemental zinc, such as zinc sulphate or zinc gluconate, to accelerate healing. The maximum tolerable intake, defined as the highest daily dose unlikely to have adverse effects on health, is 40 mg of zinc. Nausea, vomiting, diarrhoea, headaches, and cramps are some of the symptoms of zinc toxicity, beyond this 40 mg limit.
Topical application of zinc also accelerates the healing process.
It has also been demonstrated that topical zinc in wounds promotes autolytic debridement, which is the body's ability to self-dissolve dead cells/foreign bodies using enzymes such as collagenase. Indeed, zinc is a cofactor of this matrix metalloproteinase present in the dermis, the deep layer of the skin. This benefit has been observed in bedsores, diabetic foot and burns.
On the other hand, zinc also acts as a cofactor for metallothioneins, antioxidant proteins that enhance cellular resistance to apoptosis (cell death) by providing a protective effect against reactive oxygen species and bacterial toxins.
When applied topically, zinc can be administered in the form ofzinc oxide or zinc sulphate. Experimental studies comparing these two actives have demonstrated the advantages of zinc oxide in wounds compared to zinc sulphate. Zinc oxide allows for a more prolonged release of zinc and also mimics the action of certain growth factors. On the other hand, zinc sulphate is very astringent. Zinc sulphate should always be used at low concentrations, as high levels of zinc sulphate inhibit epithelialisation and increase inflammation.
What is the best route? Internal or external?
Oral supplementation with zinc sulphate is essential for wound healing in patients with zinc deficiency. If levels are normal, it is preferable to opt for a topical zinc treatment, to avoid the potential side effects that zinc ingestion may cause.
Sources
Institute of Medicine (US) Panel on Micronutrients. Dietary reference intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington D.C: National Academy Press (2001).
AGREN M. S. & al. Zinc in wound healing: theoretical, experimental, and clinical aspects. Wound Repair and Regeneration (2007).
HORNIG D. H. & al. Contribution of selected vitamins and trace elements to immune function. Annals of Nutrition and Metabolism (2007).
GARNICK M. S. & al. Zinc and wound healing: a review of zinc physiology and clinical applications. Wounds (2017).
