TRACE MINERALS :

The term trace when applied to minerals or elements

is still used and can be defined as minerals that make

up <0.01% of total body weight.

Alternately, trace may be applied to minerals needed

by the body in amounts <100 mg per day.

Iron•The human body contains 38 mg iron/kg body weight for

women and 50 mg iron/kg body weight for men.

•Over 65% of body iron is found in hemoglobin, up to

about 10% is found as myoglobin.

•The total amount of iron found in a person not only is

related to body weight but also is influenced by other

physiological conditions, including age, gender, pregnancy,

and state of growth.

SOURCES:

Heme iron represents iron that is contained with the

porphyrin ring.

Heme iron is derived mainly from hemoglobin and

myoglobin and thus is found in animal products ,especially

meat, fish, and poultry.

Nonheme iron is found primarily in plant foods (nuts,

fruits, vegetables, grains, tofu) and dairy products (milk,

cheese, eggs)

Foods high in iron, such as liver and organ meats, red

meats, oysters and clams, beans (lima, navy),dark green

leafy vegetables, and dried fruits.

Digestion & Absorption :

Heme Iron :

Heme iron must be hydrolyzed from the globin portion of

hemoglobin or myoglobin before absorption. This digestion is

accomplished by proteases in both the stomach and the small

intestine and results in the release of heme iron from the globin.

Heme, containing the iron bound to the porphyrin

ring remains soluble, especially in the presence of the

degradation products of globin, and is readily absorbed

intact across the brush border of the mucosal cell by heme

carrier protein 1.

Iron absorption occurs throughout the small intestine, but

it is most efficient in the proximal portion, particularly the

duodenum.

Within the mucosal cell, the absorbed heme porphyrin ring

is hydrolyzed by heme oxygenase into inorganic ferrous iron

and protoporphyrin.

The released iron may associate with proteins such as

mobilferrin that make up the paraferritin complex and can

be used by the intestinal mucosal cell, excreted with the

sloughing of the enterocytes, or, following transport out of

the enterocyte, used by other body tissues.

Nonheme Iron Digestion and Absorption :

Once released from food components, most nonheme iron is present

as ferric (Fe3+) iron in the stomach Ferric iron remains fairly soluble

as long as the pH of the environment is acidic.

In intestinal alkaline environment, ferric iron may complex to

produce ferric hydroxide (Fe(OH)3), a relatively insoluble compound

making the iron less available for absorption.

In contrast to ferric iron, ferrous iron remains fairly soluble at a

more alkaline pH, although some ferrous iron may be oxidized in the

alkaline pH of the intestine to the ferric form.

Ferrireductase, have been reduce ferric iron to the ferrous state.

Vitamin C is needed for reductaseactivity.

Enhancers of Iron Absorption

Some dietary factors that have been found to enhance

nonheme iron absorption include:

•sugars, especially fructose and sorbitol

•acids, such as ascorbic, citric, lactic, and tartaric

•meat, poultry, and fish or their digestion products mucin

Ascorbic acid (vitamin C), along with citric, lactic, and

tartaric acids, for example, acts as a reducing agent

andforms a chelate with nonheme ferric iron at an acid pH.

Inhibitors of Iron Absorption

Many dietary factors inhibit iron absorption, including:

•polyphenols such as tannin derivatives of gallic acid (in

tea and coffee)

•oxalic acid (in spinach, chard, berries, chocolate, and tea,

among other sources)

•phytates, also called phytic acid, inositol hexaphosphate,

or polyphosphate (in maize, whole grains, legumes)

•phosvitin, a protein containing phosphorylated serine

residues found in egg yolks

•nutrients such as calcium, calcium phosphate salts,

zinc,manganese, and nickel

Transport

Iron in its oxidized ferric state is transported in the

blood attached to the protein transferrin iron must first be

oxidized before it can bind to transferrin for transport

in the blood.

Hephaestin and ceruloplasmin, These proteins catalyze

the oxidation of ferrous iron to its ferric form so it can bind

to transferrin in the plasma.

Transferrin carries iron throughout the body, delivering

both new and recycled iron to tissues either for use or for

storage. Transferrin has a half-life of about 7 to 10 days.

Storage :

Iron not needed in a functional capacity is stored in

three main sites: the liver, bone marrow, and spleen.

Transferrin delivers iron to these sites, especially the

liver, which is thought to store about 60% of body’s iron.

The remaining 40% is found in reticuloendothelial (RE)

cells within the liver, spleen, and bone marrow (and

possibly between muscle fibers).

Ferritin is the primary storage form of iron in cells.

IRON RECYCLING

FUNCTIONS

Hemoglobin and Myoglobin

•The essentiality of iron is due in part to its presence in

heme, which functions as a prosthetic group for some

proteins.

•The atom of iron in the center of the heme molecule

enables oxygen transport to tissues (hemoglobin);

transitional storage of oxygen in tissues, particularly

muscle (myoglobin); and transport of electrons through the

respiratory chain (cytochromes).

Cytochromes and Other Enzymes Involved in Electron

Transport:

Heme-containing cytochromes in the electron transport

chain, such as cytochromes b and c, pass along single

electrons. The transfer of electrons along the chain is

made possible by the change in the oxidation state of iron.

Nonheme iron sulfur enzymes involved in electron

transport include NADH dehydrogenase, succinate

dehydrogenase,and ubiquinone–cytochrome c reductase.

Monooxygenases and Dioxygenases

Many additional enzymes involved in a variety of

processes besides the respiratory chain also require iron.

Many monooxygenases, for example, need iron.

Monooxygenases insert one of two oxygen atoms into a

substrate. Examples of iron containing monooxygenases

include:

•phenylalanine monooxygenase

•tyrosine monooxygenase

•tryptophan monooxygenase

Many dioxygenases also need iron. Dioxygenases catalyze

the insertion of two oxygen atoms into a substrate.

Many important dioxygenases in the body require iron,

including:

•tryptophan dioxygenase (amino acid metabolism)

•homogentisate dioxygenase (amino acid metabolism)

•trimethyl lysine dioxygenase and 4-butyrobetaine

•dioxygenase (carnitine synthesis)

•lysine dioxygenase and proline dioxygenase (procollagen

synthesis)

•nitric oxide synthase

Peroxidases

Other important reactions required to protect the body also

involve iron-containing enzymes.

•Catalase, with four heme groups, converts hydrogen

peroxide to water and molecular oxygen:

•Myeloperoxidase (also called chloroperoxidase), another

heme-containing enzyme, is found in the plasma as well as

in neutrophils (white blood cells)

•Thyroperoxidase, a heme-dependent enzyme, is necessary

for organification of iodide (a process in which 2 iodides

are added to tyrosine residues on thyroglobulin).

INTERACTIONS WITH OTHER NUTRIENTS :

Acorbic acid interact, enhancing iron absorption.

Without copper dependent ferroxidase activity, iron cannot be

mobilized out of tissues.

Excessive intake of nonheme iron, as may occur with supplements,

may have a detrimental effect on zinc absorption.

Reduced vitamin A status causes iron accumulation in selected

organs such as the spleen and liver.

Lead inhibits the activity of Δ-aminolevulinic acid dehydratase, a

zinc-dependent enzyme required in heme synthesis. Lead also inhibits

the activity of ferrochelatase, the enzyme that incorporates iron into

heme.

iron deficiency may affect selenium absorption or increase selenium

use in the body.

RDA: (mg/day)

•Man : 28•Women: 30•Pregnant: 38Lactation: 0 to 6 months : 38

6 to 12 months: 30

•Children :1-3 yrs :124-6 yrs: 187-9 yrs: 26

•Boys :10-12 yrs :3413-15 yrs:4116-18 yrs:50

•Girls :10-12 yrs :1913-15 yrs :2816-18 yrs:30

DEFICIENCY: IRON DEFICIENCY

WITH AND WITHOUT ANEMIA

Iron deficiency occurs most often due to inadequate iron intake.

Iron intake is frequently inadequate in four population groups:

•infants and young children (6 months to about 4 years), because of

the low iron content of milk and other preferred foods, rapid

growth rate, and insufficient body reserves of iron to meet needs

beyond about 6 months.

•adolescents in their early growth spurt, because of rapid growth

and the needs of expanding red blood cell mass.

•females during childbearing years, because of menstrual iron losses

•pregnant women, because of their expanding blood volume, the

demands of fetus and placenta, and blood losses to be incurred in

childbirth.

Conditions associated with increased iron losses include

hemorrhage, renal disease, renal replacement therapy,

decreased (faster than normal) gastrointestinal transit

time, steatorrhea, and parasites. Impaired iron

absorption may occur with protein energy malnutrition,

renal disease, achlorhydria (the absence of hydrochloricacid

in gastric juice), prolonged use of alkaline-based drugs such

as antacids, and parasites.

anemia doesnot occur until iron depletion is severe. Iron deficiency

can occur without anemia, however. Symptoms of iron deficiency,

mostly demonstrated

•In children, include pallor, listlessness, behavioral disturbances,

impaired performance in some cognitive tasks, some irreversible

impairment of learning ability, and short attention span .

•In adults, work performance and productivity are most commonly

impaired with iron deficiency. Iron deficiency may impair the

degradation of γ-aminobutyric acid (GABA), an inhibitory

neurotransmitter in the brain, or may inhibit dopamine-producing

neurons . Possible impairment of the immune system, decreased

resistance to infection,and impaired capacity to maintain body

temperature have also been seen.

TOXICITY:

Accidental iron overload (toxicity) has been observed inyoung

children following excessive ingestion of iron pills or

vitamin/mineral pills. Other people susceptible to iron overload have

a genetic disorder known as hemochromatosis-The condition is

characterized by increased (at least two times normal) iron

absorption

The absorbed iron is progressively deposited within joints and

tissues, especially the liver, heart, and pancreas, causing extensive

organ damage and ultimately organ failure.

EXCRETION

Daily iron losses for an adult male are ~0.9 to 1.0 mg/day

(12–14 mg/kg/day). Iron losses for women

(postmenopausal) are a bit lower, ~0.7 to 0.9 mg/day,

because of smaller surface area. premenopausal women are

estimated to be ~1.3 to 1.4 mg/day because of iron loss in

menses Losses of iron occur from three main sites:

1. the gastrointestinal tract

2. the skin

3. the kidneys

Zinc

The human body contains ~1.5 to 2.5 g of zinc. Zinc is

found in all organs and tissues (primarily intracellularly)

and in body fluids. Zinc, a metal, can exist in several

different valence states, but it is almost universally

found as the divalent ion (Zn2+).

Sources:

Zinc is found in foods complexed with amino acids that are part

of peptides and proteins and with nucleic acids.

Very good sources of zinc are red meats (especially organ meats)

and seafood

Other good animal sources of zinc include poultry, pork, and dairy

products. Whole grains (especially bran and germ) and vegetables

(leafy and root) represent good plant sources of zinc. Fruits and

refined cereals are poor

zinc sources.

DIGESTION, ABSORPTION, TRANSPORT, UPTAKE, AND STORAGE

Digestion

Zinc, like iron, needs to be hydrolyzed from amino acids and nucleic acids

before it can be absorbed.

Zinc is believed to be liberated from food during the digestive process, most

likely by proteases and nucleases in the stomach and small intestine.

Absorption

The main site of zinc absorption in the gastrointestinal tract is the proximal

small intestine, most likely the jejunum.

Zinc is absorbed into the enterocyte by a carrier-mediated process, with low

zinc intakes absorbed more efficiently than higher intakes. A protein carrier

called Zrt- and Irt-like protein (ZIP)4 is thought to be the primary

transporter of zinc across the brush border membrane of the enterocyte

High doses of zinc that can be absorbed by other means, especially by

diffusion.

Factors Influencing Zinc Absorption

Phytates, calcium and copper and iron interfere while small

peptides and amino acid promotes absorption.

Transport

Zinc passing into portal blood from the intestinal cell is

mainly transported loosely bound to albumin. Most zinc is

then taken to the liver, where the mineral is initially

concentrated. Zinc leaving the liver is transported in the

blood still bound to albumin, Albumin is thought to

transport up to ~60% of zinc in the blood.

Distribution and Storage

Zinc is found in all body organs, most notably the liver,

kidneys, muscle, skin, and bones.

Zinc is thought to be stored in most tissues as part of the

protein thionein, which when mineral bound is known as

metallothionein.

FUNCTIONS

•Zinc is essential components of several enzymes like Carbonic anhydrase,

found primarily in the erythrocytes and in the renal tubule, is essential for

respiration.

•Alkaline phosphatase contains four zinc atoms per enzyme molecule.

Alcohol dehydrogenase This enzyme is important in the conversion of alcohols

to aldehydes.

•Carboxypeptidase an exopeptidase secreted by the pancreas into the

duodenum, is necessary to digest protein

•Aminopeptidase is also involved in protein digestion

•Superoxide dismutase (SOD) found in the cell cytoplasm requires two atoms

each of zinc and copper for function; zinc appears to have a structural role in

the enzyme

•Collagenases help to digest collagen in the gastrointestinal tract. Zinc plays a

catalytic role in the enzyme’s function.

•Phospholipase C requires three zinc atoms for catalytic activity.

This enzyme hydrolyzes the glycerophosphate bond in phospholipids.

•Polyglutamate hydrolase, is a zinc-dependent enzyme necessary to

digest folate

•Polymerases, kinases, nucleases, transferases, phosphorylases,and

transcriptases all require zinc.

Other Roles:

Physiological functions of zinc include tissue or cell growth, cell

replication, bone formation, skin integrity,cell- mediated immunity,

and generalized host defense.

INTERACTIONS WITH OTHER NUTRIENTS

•zinc is necessary for the hepatic synthesis of retinol-binding

protein,which transports vitamin A in the blood

•Cadmium appears to bind to sites to which zinc would normally

bind and to disrupt normal zinc functions

•Diminished calcium absorption has been observed with ingestion of

zinc supplements when calcium intake is low (<300 mg calcium).

•There isdetrimental effect of excessive zinc intake on copper

absorption.

RDA:

The daily requirements for zinc for adult men and women were set

as:

•9.4 mg and 6.8 mg, respectively, and the RDAs were set at 11 mg

and 8 mg, respectively.

•The zinc recommendation for lactating women is 12 mg/day.

•RDA for zinc during pregnancy is 11 mg/day to cover the

calculated need for growth of the fetus and placenta.

EXCRETION

The three primary routes of zinc loss from the body are

through the:

1. gastrointestinal tract

2. kidneys

3. skin (integument and sweat)

Most zinc is lost from the body through the gastrointestinal

tract in the feces.

DEFICIENCY

Some population groups, especially the elderly and vegetarians, have been

found to consume less than adequate amounts of zinc. Conditions associated

with an increased need for intake include alcoholism, chronic illness,

stress, trauma, surgery, and malabsorption.

Signs and symptoms of zinc deficiency are growth retardation skeletal

abnormalities from impaired development of epiphyseal cartilage, defective

collagen synthesis or cross-linking, poor wound healing, dermatitis (especially

around body orifices), delayed sexual maturation in children, hypogeusia

(blunting of sense of taste), alopecia (hair loss), impaired immune function,

and impaired protein synthesis.

Acrodermatitis enteropathica is a rare inherited metabolic disease of zinc

deficiency caused by a defect in absorption of Zn from the intestine.

TOXICITY

Excessive intake of zinc can cause toxicity. An acute

toxicity with 1 to 2 g zinc sulfate (225–450 mg zinc) can

produce a metallic taste, nausea, vomiting, epigastric pain,

abdominal cramps, and bloody diarrhea [34]. Chronically

ingesting zinc in amounts of about 40 mg (lower for some

people) results in a copper deficiency [33,34]. The tolerable

upper intake level for zinc has been set at 40 mg daily based

on this interaction with copper.