ZINC IN NUTRITION

1509, recognized as element Essentiality demonstrated

Plants: 1869 Animals: 1934

Deficiency Considered unlikely until 1955

conditioned human deficiency demonstrated in 1956

1961, hypogonadal dwarfism suggested to be zinc deficiency

sources

Relatively abundant mineral Good sources: shellfish, beef and other red meats Slightly less good: Whole-grains

most in bran and germ portions 80% lost to milling phytates, hexa & penta phosphates depress

absorption P/Zn ratios of 10 or more

Relatively good sources: nuts and legumes Eggs, milk, poultry & fish diets lower than

pork, beef, lamb diets High meat diets enhance absorption

280g or 10 oz fits right into food pyramid guide cys & met form stable chelate complexes

Zinc absorption is greater from a diet high in animal protein than a diet rich in plant proteins . Phytates, which are found in whole grain breads, cereals, legumes and other products, can decrease zinc absorption .

Distribution

Whole body: 1.5g (female)-2.5g (male) Skeletal Muscle 57% Bone 29% Skin 6% Liver 5% Brain 1.5% Kidneys 0.7% Heart 0.4% Hair ~0.1% Blood Plasma ~0.1

sources

Foods contain element zinc, much of it bound to protein or DNA.

Oysters (> 70 mg per

serving).

Meats (2-3 mg/100g).

Shellfish (2.7 mg/100g)

Other good food sources include: beans, nuts, certain seafood,

whole grains, fortified breakfast cereals, and dairy products .

Role of Zinc

Required for growth in children and infants.

absorption

GIT modulates the quantity of exogenous dietary zinc absorbed and the quantity of endogenous zinc excreted

More than 70% of a small zinc dose (less than 3 mg) is absorbed from the small intestine.

Maximum absorption occurs in duodenum

There is sustained release from enterocytes into portal circulation for ~ 9h

Zinc absorption mainly achieved by 2 families of zinc transporters;

1. ZIP Family2. ZnT Family

Excretion

Routes: intestine, kidneys, integument, and semen

After a meal, maximum zinc secretion occurs through pancreatobiliary secretions

Maximum reabsorption occurs from mid-jejunum and ileum

Total amount excreted = Amount secreted – Amount reabsorbed

Excretion of endogenous zinc by the intestine depends on the ‘zinc status’ of the body.

Zinc deficiency

Causes; Malnutrition Alcoholism Malabsorption Burns Chronic renal disease Acrodermatitis enteropathica

Signs Growth retardation Delayed sexual maturation & impotence

Impaired testicular development Hypogonadism & hypospermia Alopecia Acroorifical skin lesions

Other, glossitis, alopecia & nail dystrophy Immune deficiencies Behavioral changes

Night blindness Impaired taste (hypoguesia) Delayed healing of wounds, burns, decubitus

ulcers Impaired appetite & food intake Eye lesions including photophobia & lack of

dark adaptation

Zinc deficiency

1. Severe dermatitis, alopecia, diarrhea, emotional disorder,

weight loss, infections, hypogonadism in males2. Moderate

growth retardation and delayed puberty in adolescents, hypogonadism in males, rough skin, poor appetite, mental lethargy, delayed wound healing, taste abnormalities and abnormal dark adaptation

3. Mild oligospermia, slight weight loss and

hyperammonaemia

Deficiency during pregancy

Zn deficient rats failed to conceive Abnormalities of blastocyst development Offspring had high incidence of

abnormalities Deformities of brain, skull, limbs, eyes, heart,

lungs Low Zn intake during the third trimester

may not have such profound effects Main stages of differentiation are already

complete Can result in low birth weight, and prolonged

and difficult parturition

(Left) This boy has a zinc deficiency, and his hair is very thin and sparse; (right) after treatment his hair is

growing more strongly)

Zinc toxicity

Excess accumulation within cells may disrupt functions of biological molecules Protein, enzymes, DNA

Leads to toxic consequences Anemia

Impaired copper availability Acute excessive intakes

Local irritant to tissues and membranes GI distress, nausea, vomiting, abdominal cramps,

diarrhea Relatively non-toxic

Sources of exposure – drinking water, feed, polluted air

Acrodermatitis enteropathica

Genetic disorder of zinc absorption. Presents during infancy. Characterized mainly by a triad

consisting of1. Acral dermatitis2. Alopecia3. diarrhea

Age

In infants bottle fed with bovine milk, days to week, breast fed infants soon after feeding

In older children its acquired zinc deficiency.

Etiology

Acrodermatitis enteropathica; autosomal recessive trait resulting in failure to absorb zinc.

Acquired zinc deficiency; secondary to reduced dietary intake , malabsorption, increased urinary loss, etc.

Clinical evaluation

Skin mucous membrane and hair are involved.

Lesions are pink and later become brightly erythematous.

Impaired wound healing. Irritable with depressed mood Growth failure

Other symptoms

Loss of weight Sensitivity to light Diarrhea Conjuctivitis Red glossy tongue and mouth ulcers

Investigations

Complete blood count Serum/ plasma zinc levels Urine; zinc excretion is reduced Dermatopathology; intraepidermal clefts

and blisters

treatment

1mg/kg body weight of oral zinc supplementation per day of life.

Zinc gluconate better tolerated than sulfate.

Dietary or iv supplementation with zinc salts with two or three times , the RDA restores normal zinc status in days or week.

5 days of zinc replacement

Treatment of diarrhea

All children above 6months should receive a uniform dose of 20mg elemental zinc as soon as diarrhoea starts and continue for 14 days.

2 to 6mnths- 10mg/day for 14 days.