Zinc

The most readily available form of zinc occurs in animal flesh, particularly red meats and poultry. Meat intake is frequently low among preschoolers, occasionally because of personal preferences or socioeconomic reasons, but usually because meats are displaced by cereal foods, milk and milk products that children tend to prefer. Observation led to the fortification of infant and children’s foods, especially cereals, with zinc. Milk is a good source of zinc, but high intakes of calcium from milk may interfere with the absorption of iron and zinc. The phytates from a whole grains in unleavened breads may limit zinc absorption in some populations. 

Deficiencies are less likely to be a problem in Western nations, where breads, breakfast, foods, and other cereal-based foods are made primarily from refined grains and are typically fortified.

‘’Nutritionally dwarfed’’ boys, characterized by short stature, iron deficiency anemia, and delayed sexual maturity, showed remarkable improvements with zinc supplementation. Some grew as much as 5 inches in 1 year and had parallel progression in gonadal development. The primary cause of zinc deficiency in these boys was identified as an impoverished diet consisting mainly of fibrous, unleavened bread. Although the whole grains used to make the bread were relatively high in zinc, they also contained phytates, which are known to form insoluble complexes with zinc and iron.

Children with severe zinc deficiency, as measured by plasma zinc concentrations, have been found to be at increased risk for diarrhea and respiratory diseases. Therefore adequate zinc status plays a central role not only in growth and health promotion but also in disease prevention.

Zinc is abundantly distributed throughout the human body and is second only to iron among trace elements. The human body has approximately 2 to 3 g of zinc, with the highest concentrations in the liver, pancreas, kidney, bone, and muscles. Other tissues with high concentrations include various parts of the eye, prostate gland, spermatozoa, skin, hair, fingernails, toenails.

Low zinc intakes are associated with low concentrations of insulin-like growth factor 1 in postmenopausal women. If calcium supplements are taken by postmenopausal women, it is possible that zinc absorption becomes suppressed, reducing insulin-like growth factor 1, which normally supports tissue growth. Problems caused by low zinc intakes seem to be increasing, partly because of the low bioavailability of zinc. Athletes may also have an increased risk for developing zinc deficiency. Physical activity may increase mobilization of zinc from bones stores for cellular needs. 

Dietary reference intake

Infants 2-5 mg/day

Children 5-8 mg/day

Adolescents 8-11 mg/day

Adults 8-11 mg/day

Pregnant 11-13 mg/day

Lactating 12-14 mg/day

Zinc content of selected foods

Baked beans, with pork, ½ cup (6.9 mg)

Ground beed, lean, 3 oz (5.3 mg)

Beef liver, fried, 3 oz (4.5 mg)

Oysters, eastern, 3 oz (3.9 mg)

Turkey, dark meat, baked, 3 oz (3.8 mg)

Pork, cooked, 3 oz (3.5 mg)

Ham, cooked, 3 oz (2.2 mg)

Wild rice, cooked, ½ cup (2.2 mg)

Peas, green, cookes, 1 cup (1.2 mg)

Yogurt, plain, 8 oz (1.3 mg)

Pecans, 1 oz (1.3 mg)

Deficiency

Growth retardation

Delayed sexual maturation

Hypogonadism and hypospermia

Alopecia

Delayed wound healing

Skin lesions

Impaired appetite

Immune deficiencies

Behavioral disturbances

Eye lesions, including photophobia and night blindness

Impaired taste (hypogeusia)

Toxicity

Anemia

Fever

Central nervous system disturbances

GI irritation and vomiting