Nutrition and cutaneous wound healing

Abstract

Wound healing is a complex and energy-demanding process. The relationship between nutrition and wound healing has been recognized for many centuries. Several studies have indicated that nutritional deficiencies are more prevalent among patients with chronic wounds. Malnutrition may alter the inflammatory response, collagen synthesis, and wound tensile strength, all of which are crucial for wound healing. Although the specific role of nutrition and supplementation in wound care remains uncertain, it is necessary to identify and correct nutritional imbalances to avoid any potential deterioration of the healing process. It is also important to recognize the differences in pathophysiology between acute and chronic wounds. A burn, surgical, or a traumatic wound is different from a diabetic foot ulcer, which is different from a pressure ulcer. Chronic wounds are more prevalent in the aging population, and patients often have underlying comorbidities, such as diabetes mellitus, peripheral vascular disease, connective tissue disease, or other systemic illnesses that may alter energy metabolism and contribute to impaired healing. Management approaches to acute wound care may not apply universally to chronic wounds. In this review, we discuss the available data and possible roles for nutrition in wound healing.

Introduction

Ancient Mesopotamians observed that the wounds of dogs healed faster when a dog had licked them.¹ In Mesopotamia, dogs were associated with two powerful Sumerian deities. Inanna, the goddess of love, fertility, and war, was often accompanied by a pack of hunting dogs.¹ Gula was the goddess of healing and had dogs as her symbol.² Gula's dogs were associated with legends about the healing power of canine saliva.¹ Contemporary studies have shown that saliva contains a massive cocktail of proteins (>1,000 proteins) that function collectively. Saliva is mitogenic, enhances cell migration, and also acts as a bactericidal agent, thus promoting wound healing.3, 4, 5, 6

Wound repair is an energy-demanding process. Human energy is derived by breaking chemical bonds of nutrient molecules, mainly carbohydrates, lipids, and proteins. Organic acids, polyols (artificial sweeteners), ethanol, and fibers are additional sources of energy; nevertheless, energy metabolism is tightly regulated, and different cell types require different fuel molecules. Adequate nutrition is important to preserve skin and tissue viability, and it is essential for the prevention of infection, which could have deleterious effects on wound healing.^7,8 Research on the role of nutrition in wound healing has been inadequate, and the majority of the scientific evidence for this topic is derived from studies related to pressure ulcers (PUs). Such studies, despite methodologic shortcomings, have suggested a strong correlation between poor nutritional status and PU development. Stages of PU are affected by the degree of malnutrition. The prevention of malnutrition leads to risk reduction for PU formation.9, 10, 11, 12, 13, 14 Older adults who are considered undernourished, in addition to a myriad of other factors, are more at risk for developing PUs and other complex wounds.15, 16, 17

Although undernutrition is a primary concern, obesity may also contribute to impaired healing. Obesity is defined as abnormal or excessive fat accumulation that presents a risk to health. A person with a body mass index (BMI) of 30 or more is generally considered obese. Obesity is a significant risk factor for a number of chronic diseases, including diabetes, cardiovascular diseases, and cancer.18, 19, 20 Malnutrition represents the status of nutrition in which a deficiency or imbalance of energy, protein, and other nutrients causes measurable adverse effects on tissue structure and function with untoward clinical outcomes. A consensus statement by the Academy of Nutrition and Dietetics and the American Society of Parenteral and Enteral Nutrition published in May 2012 defines malnutrition as the presence of two or more of the following characteristics²¹:

• Insufficient energy intake

• Weight loss

• Loss of muscle mass

• Loss of subcutaneous fat

• Localized or generalized fluid accumulation that may sometimes mask weight loss

• Diminished functional status as measured by handgrip strength

• Normal wound healing progresses through four overlapping phases^22,23:

• Coagulation

• Inflammation

• Migration-proliferation (including matrix deposition)

• Remodeling

Acute wounds, such as those created by trauma or surgery, occur suddenly and heal in a relatively predictable time frame. A chronic wound is a wound that fails to progress through the normal phases of healing in an orderly and timely manner.²⁴ Persistent inflammation is a hallmark of the chronic wound microenvironment.²⁵ Some of the major underlying causes of impaired healing include diabetes mellitus, vascular disease, and prolonged mechanical pressure. Of note, the risk of developing chronic illnesses and physiologic limitations increases with aging.²⁶

Malnutrition is known to increase the risk of infection, impaired wound healing, and reduced tensile strength.27, 28, 29, 30 Depletion of protein and minerals has been associated with increased risk of developing chronic ulcers, hair loss, and nail dystrophies.31, 32, 33 A few examples of skin diseases owing to nutritional deficiencies include beriberi (vitamin B1 deficiency) and acrodermatitis enteropathica (zinc deficiency).

Nutrient deficiencies have been found in some patients with cutaneous wounds; however, the role of nutritional supplementation is unclear. In part, this may be attributed to the fact that nutrition is not an exact science. There are significant variations owing to health status, age, and sex, as well as geographic, socioeconomic, and racial factors.³² Unfortunately, there remains a paucity of good data on appropriate screening of patients, supplementation protocols, and their efficacies. This contribution reviews available data for the roles of nutrients required for biologic processes in the skin and their involvement in wound healing (Table 1).