Nutrition Iron Quiz

Iron & Porphyrin Metabolism

• Iron is the most abundant element on Earth but only trace amounts are found in living cells.
• Most iron in the human body is in the porphyrin ring of heme, incorporated into proteins like hemoglobin, myoglobin, catalase, peroxidases, and cytochromes.
• An average adult male/female has 4-5 grams of iron in their body.
• 65-70% of iron is in hemoglobin, 10% in myoglobin and other enzymes, and 20-25% is in storage form.
• Daily iron requirement depends on age, gender, and physiological status.
• Approximately 1 mg of iron is lost daily through shedding cells lining the gastrointestinal and urinary tracts.
• A small number of erythrocytes are lost in urine and feces.
• Men and postmenopausal women require approximately 1 mg of iron absorption per day.
• Women of childbearing age need 2 mg per day to compensate for menstrual blood loss.
• Pregnant and lactating women have increased iron demands (3-4 mg).
• The growing fetus, blood loss during delivery, and feeding an infant increase the daily iron demand in pregnant women.

Types of Iron

• Two types of absorbable dietary iron exist: heme and non-heme.
• Heme iron, derived from hemoglobin and myoglobin in animal products (meat, seafood, poultry), is the most easily absorbed (15-35%) and contributes significantly to total iron absorption (10% or more).
• Non-heme iron is derived from plants and fortified foods and is less readily absorbed.
• A healthy diet contains 10-20 mg of iron per day.
• Only 5-10% of this amount is absorbed, primarily in the duodenum and upper small intestine.
• Most dietary iron is ferric (Fe³⁺) and must be converted to ferrous (Fe²⁺) to enter epithelial cells.
• The brush border enzyme, ferric reductase, converts ferric iron to ferrous iron.

Iron Absorption & Transport

• Ferrous iron is transported into cells by a divalent metal transporter (DMT1).
• Substances like phosphates (eggs, cheese, milk), oxalates, phytates (vegetables), and tannates (tea) form insoluble complexes with iron, reducing absorption.
• Heme iron is absorbed separately, directly by cells.
• In epithelial cells, iron is incorporated into ferritin for storage or transferred to the blood.
• Iron is toxic in free form, so it is bound to transferrin.
• Each transferrin has two binding sites, typically 20-50% saturated with iron.
• Transferrin carries iron to cells via specific surface receptors.
• The holo-transferrin-receptor complex is internalized by endocytosis.
• The acidic environment in the endocytic vesicle releases iron from transferrin.
• Released iron is used for heme synthesis or stored as ferritin.
• Iron stores in tissues are primarily ferritin (readily mobilized) and hemosiderin (insoluble, a derived form from ferritin, not as readily mobilized).
• One-third of body iron reserves are in the liver, one-third in the bone marrow, and the remainder in the spleen and other tissues.

Iron Balance Control

• Iron loss is continuous and largely not controllable; iron absorption is controlled by changes in absorption.
• Major factors affecting iron absorption are body iron stores and red blood cell production rate.
• Iron absorption and tissue distribution of iron is mainly controlled by the hepatic hormone hepcidin's interaction with ferroportin.
• Ferroportin is expressed in iron-storing and transport tissues; it's also the sole cellular exporter of elemental iron in multicellular organisms.

Pathological Conditions: Iron Deficiency

• Iron deficiency is the most common nutritional disorder and cause of anemia in humans.
• It is more frequent in women, individuals with low socioeconomic status, those with gastrointestinal surgery, and patients with chronic diarrhea.
• Iron deficiency develops in stages when iron reserves become exhausted; biochemical tests of iron metabolism become abnormal even if anemia isn't yet apparent.
• Next steps in development are a decrease in hemoglobin concentration and paler red blood cells (hypochromic).
• In full iron-deficiency anemia, MCV, MCH, and MCHC are also decreased.
• Examination of peripheral blood smears shows hypochromic, microcytic, and anisocytosis (abnormal size and shape of erythrocytes).
• Laboratory tests to diagnose differentiate iron deficiency from other types of hypochromic, microcytic anemia include serum iron (low), total iron-binding capacity (TIBC) (high), transferrin saturation (low), serum ferritin (low), and free erythrocyte protoporphyrin (FEP). (high).

Pathological Conditions: Iron Overload

• Hereditary hemochromatosis is a genetic disease characterized by progressive iron store increase, leading to organ impairment.
• Patients with hereditary hemochromatosis may absorb 4 mg or more of iron per day, even on a typical diet.
• Excessive iron deposits in the liver, pancreas, heart, skin, and other organs are a hallmark.
• Iron overload can also be acquired from ineffective erythropoiesis (e.g., beta-thalassemia major), blood transfusions, or medicinal iron supplements.

Lab Tools for Iron Metabolism

• Clinically, three iron compartments account for 90% of total iron: hemoglobin (largest pool, measured via CBC), serum iron/transferrin, and serum ferritin.
• The combination of these tests helps identify iron metabolism disorders.

Complete Blood Count (CBC)

• A complete blood count provides the number of erythrocytes, hemoglobin concentration, and red blood cell indices.
• The World Health Organization (WHO) defines anemia as hemoglobin concentrations less than 13 g/dL in men, <12 g/dL in women, and <11 g/dL in pregnant women.
• Iron deficiency causes hypochromic, microcytic anemia, reducing values of MCV, MCH, and MCHC.
• Hypochromic, microcytic anemias are often characteristic of thalassemia trait, sideroblastic anemia, and anemia of chronic disease.
• RBC parameters indicate the presence of anemia but not necessarily the cause.

Serum Iron, TIBC, and Transferrin Saturation

• Serum iron concentration fluctuates significantly, even among healthy individuals and across the day.
• Diurnal variations limit the diagnostic usefulness of individual serum iron values.
• Iron values should always be evaluated with TIBC (measures the max amount of iron serum proteins can bind).
• Transferrin saturation is calculated by dividing serum iron by TIBC and provides an estimate of occupied transferrin binding sites.

Serum Ferritin

• A small amount of ferritin circulates in plasma as iron-free apoferritin.
• Serum ferritin levels accurately reflect the amount of storage iron.
• Low serum ferritin values typically indicate iron deficiency (before serum iron and transferrin saturation show a significant change).
• Elevated serum ferritin levels are a sign of iron overload.

Heme Synthesis and Porphyrias

Porphyrias

• Porphyrias are genetically determined disorders affecting heme synthesis.
• Deficiencies in seven enzymes involved in heme synthesis have been recognized.
• Most porphyrias are inherited as autosomal dominant traits.
• Excess porphyrins and their precursors accumulate behind the deficient enzyme, and these excesses are excreted in bodily tissues and fluids.
• This excretion is a basis for diagnosing porphyrias.

Neurological Porphyrias

• Four porphyrias are linked to acute episodes of abdominal pain, neurological issues, and/or psychiatric disturbances.
• These include acute intermittent porphyria, variegate porphyria, hereditary coproporphyria, and ALA dehydratase deficiency.
• Attacks commonly involve elevated ALA and PBG excretion.

Cutaneous Porphyrias

• Three porphyrias primarily affect the skin, involving excess porphyrins, photosensitivity, and skin lesions.
• The most common cutaneous porphyria is porphyria cutanea tarda (PCT).
• PCT results from partial deficiencies in uroporphyrinogen decarboxylase.
• Other cutaneous porphyrias include protoporphyria and congenital erythropoietic porphyria.

Delta-Aminolevulinic Acid (ALA)

• Urinary ALA values are elevated in all neurological porphyria cases.
• ALA excretion also increases in lead poisoning.

Test your knowledge on iron's role in the human body with this quiz. Questions cover iron absorption, dietary sources, and physiological needs across different life stages. Perfect for anyone studying nutrition or health sciences.