Zinc is one of the essential trace elements required by the human body, second only to iron in terms of abundance. Zinc plays a crucial role in fetal development, cognitive functions in children, growth and development, metabolism, and tissue repair. Zinc deficiency arises from insufficient intake or metabolic disturbances, leading to clinical manifestations such as loss of appetite, growth retardation, dermatitis, and pica, and is classified as a nutritional deficiency disorder.
Etiology
Insufficient Intake
Animal-based foods are rich in zinc and are easily absorbed, while nuts (e.g., walnuts, chestnuts, peanuts) also contain significant amounts of zinc. However, plant-based foods generally contain less zinc, making vegetarians more susceptible to deficiency. Total parenteral nutrition without zinc supplementation can also result in zinc deficiency.
Absorption Impairment
Diarrhea, resulting from various causes, can impede zinc absorption. Cereal-based foods containing high levels of phytates and dietary fiber can bind to zinc, reducing its absorption. Cow's milk has a zinc content similar to human milk but exhibits lower absorption rates. Acrodermatitis enteropathica, an autosomal recessive genetic disorder, causes severe zinc deficiency due to impaired intestinal zinc absorption.
Increased Demand
Increased demand for zinc occurs during rapid growth phases in infants, tissue repair processes, or recovery from malnutrition. Failure to replenish zinc adequately under such conditions can result in deficiency.
Excessive Loss
Conditions such as recurrent bleeding, hemolysis, extensive burns, chronic kidney disease, long-term dialysis, proteinuria, and the use of metal chelators (e.g., penicillamine) can lead to excessive zinc loss, resulting in deficiency.
Clinical Manifestations
Digestive Dysfunction
Zinc deficiency affects the renewal of taste bud cells and the activity of salivary phosphatases, leading to hyperplasia and parakeratosis of the tongue's mucosa. This results in reduced sensitivity of taste perception, causing poor appetite, anorexia, and pica.
Growth and Developmental Delays
Zinc deficiency hinders the function of the growth hormone axis and the maturation of the gonadal axis, manifesting as growth retardation, short stature, and delayed sexual development.
Impaired Immune Function
Zinc deficiency can lead to T lymphocyte dysfunction, increasing susceptibility to infections.
Cognitive Developmental Delay
Zinc deficiency disrupts DNA and protein synthesis in brain cells and reduces glutamate concentrations in the brain, resulting in delayed cognitive development.
Other Symptoms
Hair loss, rough skin, dermatitis, geographic tongue, recurrent oral ulcers, delayed wound healing, reduced retinol-binding protein levels leading to night blindness, and anemia may occur.
Laboratory Analysis
Serum zinc levels are a reliable and widely used laboratory indicator. Mild to moderate zinc deficiency may not immediately reflect in serum zinc concentrations. The current lower limit for serum zinc in children under ten years of age is recommended to be 65 μg/dL.
Diagnosis
The diagnosis is primarily based on medical history, clinical manifestations, and serum zinc levels. Experimental zinc supplementation in children with high-risk factors for zinc deficiency can provide diagnostic confirmation through therapeutic response.
Treatment
Treating the Underlying Cause
Addressing the primary condition causing zinc deficiency is essential.
Dietary Intervention
Emphasis is placed on the intake of zinc-rich animal-based foods, such as liver, fish, lean meat, poultry, eggs, and shellfish (e.g., oysters). Colostrum is also rich in zinc.
Zinc Supplementation
Zinc supplementation options include zinc gluconate or zinc sulfate. A daily dosage of 0.5–1.0 mg/kg of elemental zinc, with a maximum of 20 mg per day, is typically administered for a course of three months.
Zinc supplementation is relatively safe, but excessive doses can lead to gastrointestinal discomfort, such as stomach upset, nausea, vomiting, diarrhea, or symptoms of dehydration and electrolyte imbalance. Zinc toxicity may cause copper deficiency, anemia, neutropenia, and reduced cytochrome oxidase activity in liver cells.
Prevention
Promoting breastfeeding and maintaining a balanced diet are key measures for preventing zinc deficiency. Strategies also involve avoiding picky eating, selective eating, and excessive snacking. For at-risk conditions such as preterm birth, formula feeding, malnutrition, chronic diarrhea, or extensive burns, appropriate zinc supplementation is recommended.