What is zinc?
Zinc is a trace element essential (metal) that is found in almost every cell of the body. Zinc supports the activity of over 100 enzymes and is essential for growth and development and protein synthesis.
Where is zinc stored in the body?
Zinc is primarily stored intracellularly. High levels are found in choroidal tissue of the eyes, prostrate, kidneys, liver, muscles and bones.
What is the mechanism of action of zinc in the body?
The mechanism of action of zinc is not known but in children with diarrhea and respiratory infections, zinc supplementation increases growth and circulating insulin-like growth factor I (IGF-I).
What are the uses of zinc in children?
Currently zinc is in the treatment of acute diarrhea as adjunct to oral rehydration. A uniform dose of 20 mg of elemental zinc should be given during the period of diarrhea and for 7 days after cessation of diarrhea in children older than 3 months. Recommendations for below 3 months must await further research.
Zinc is also recommended as part of routine, standard case management in persistent diarrhea and in those with severe malnutrition.
Patients with pneumonia have been found to have lower blood zinc levels as compared to uninfected children. Even in well nourished children suffering from acute lower respiratory infection, serum zinc levels have been found to be lower.
It is also used in treatment of Wilson's disease. Wilson's disease is an autosomal recessive disorder characterized by failure of biliary excretion of excess copper. This excess copper causes liver or brain damage. Zinc blocks the absorption of copper and increases copper excretion in the stool.
Zinc has been found to be useful as an adjunct in patients with malaria, for better wound healing and also for treatment of pica but further evidence is required for qualifying its use in these conditions.
What are signs and symptoms of zinc deficiency?
Because zinc is required for many functions in the body, deficiency of zinc can lead to a wide variety of symptoms and clinical manifestations. Clinical features of zinc deficiency include growth retardation, hair loss, diarrhea, delayed sexual maturation and hypogonadism, eye and skin lesions, and loss of appetite. Continued deficiency can lead to delayed wound healing, immune dysfunction, thymic atrophy, acrodermatitis enteropathica and lymphopenia. Zinc deficiency in the pregnant woman can lead to intrauterine growth retardation.
Since many of these symptoms are general and are associated with other medical conditions, clinical diagnosis of zinc deficiency may be difficult.
How is zinc deficiency diagnosed?
There is no single laboratory test that adequately measures zinc nutritional status. Zinc deficiency can be suspected by estimating plasma zinc level. Normal serum zinc levels in children are 66 to 194 µg/10 ml.
What is acrodermatitis enteropathica?
It is an autosomal recessive condition and is characterized by failure of zinc absorption, growth retardation, hypogonadism, eczematoid skin lesions, diarrhea and poor appetite and alopecia. Daily zinc supplementation (20-40 mg/day) results in recovery. Untreated it progresses to severe malnutrition, recurrent intercurrent infections and eventually death.
Figure 1: Acrodermatitis enteropathica showing characteristic skin lesions
What is the required daily allowance (RDA) of zinc?
The RDA of zinc as per the age and gender of the child.
Which foods are rich in zinc?
||For infants till 6 months of age, 2mg/day of daily intake of zinc is required.
||In children from 7 months to 3 years, the RDA of zinc is 3 mg/day
||Between 4-8 years of age, the RDA of zinc is 5mg/day
||Between 9-13 years of age, the RDA of zinc is 8 mg/day
||After 14 years of age, the RDA of zinc is 11mg/day in males and 8-9mg/day in females.
||During pregnancy, RDA of zinc increases by 3mg/day and during lactation increases by 4mg/day
Zinc is found in a wide variety of foods. Oysters contain highest amount of zinc than any other food. Other good sources of zinc are red meat, poultry, beans, nuts, certain seafood, whole grains, fortified breakfast cereals, and dairy products.
Who is prone to get zinc deficiency?
Cereal diets rich in phytates decrease the absorption of zinc by binding to zinc. Thus zinc deficiency is more common in developing countries that have this kind of diet. Vegetarians are also prone to zinc deficiency. Diarrhea results in a loss of zinc. Individuals who have had gastrointestinal surgery or who have digestive disorders that result in malabsorption, including tropical sprue, Crohn's disease and short bowel syndrome, are at greater risk of a zinc deficiency.
Zinc losses can occur in the urine from use of diuretic drugs caffeine, ACE inhibitors, chelating agents, burns, trauma and hemolytic anemia. Sodium valproate, ethambutol also decrease the serum zinc levels. Genetic mutations can lead to zinc depletion by increasing zinc loss in the GI tract or through sweat. Cellular zinc may be depleted by stress or illness. Too much supplementary iron can interfere with zinc absorption.
How is zinc deficiency treated?
Zinc supplements in doses of 35-40 mg daily can be used for treatment of zinc deficiency. In patients with diarrhea, a uniform dose of 20 mg of elemental zinc should be given during the period of diarrhea and for 7 days after cessation of diarrhea in children older than 3 months.
What happens if too much zinc is ingested?
Excess intake of zinc can lead to zinc toxicity. Zinc toxicity can be acute or chronic. Zinc supplement in amounts of 2 gm/day can lead to acute toxicity leading to nausea, vomiting, abdominal pain, diarrhea, convulsions. Prolonged intake of over 150 mg of zinc per day can lead to low copper, altered iron function, reduced immune function and decreased level of high-density lipoprotein. Chronic toxicity can lead to lethargy, anemia, neutropenia and CNS disturbances predominantly due to lowering of copper levels.