Iron Absorption and Sources

Iron

• Iron exists in two forms in food: heme iron (animal source) and nonheme iron (animal and plant sources)
• Heme iron has high bioavailability and isn't affected by dietary factors
• Factors that enhance nonheme iron absorption include MFP factor, Vitamin C, citric acid, lactic acid, HCl from stomach, and sugars
• Factors that inhibit nonheme iron absorption include phytates, fibers, oxalates, calcium and phosphorus in milk, tannic acid, and EDTA
• Heme iron accounts for about 10% of daily iron intake and is well absorbed (about 25%)
• Nonheme iron accounts for the remaining 90% but is less well absorbed (about 17%)
• All iron in plant-derived foods is nonheme iron
• Iron absorption is regulated by mucosal cells in the intestine
• If the body needs iron, mucosal ferritin releases iron to mucosal transferrin which hands off iron to another transferrin to travel in the blood to the rest of the body
• If the body doesn't need iron, it's excreted in shed intestinal cells

Iron Absorption, Transport, & Recycling

• Some iron loss occurs via sweat, skin, and urine
• Transferrin carries iron in the blood
• Liver and spleen dismantle red blood cells, package iron into transferrin, and store excess iron in ferritin and hemosiderin
• Bone marrow incorporates iron into hemoglobin of red blood cells and stores excess iron in ferritin and hemosiderin
• Iron-containing hemoglobin in red blood cells carries oxygen
• Some iron is delivered to myoglobin in muscle cells
• Some iron is lost if bleeding occurs

Iron Deficiency and Anemia

• Iron deficiency is depleted iron stores
• Iron-deficiency anemia is a severe depletion of iron stores, also called microcytic hypochromic anemia
• Symptoms of iron deficiency include fatigue, weakness, headaches, apathy, pallor, and poor resistance to cold temperatures
• Iron deficiency impairs energy metabolism, neurotransmitter synthesis, physical work capacity, and mental productivity
• Pica (eating non-food substances) is a characteristic behavior of iron deficiency, and common in women and children from low-income groups

Iron Toxicity (Iron Overload)

• Known as hemochromatosis, often caused by a genetic disorder enhancing iron absorption
• Repeated blood transfusions and massive supplemental iron doses can also lead to iron overload
• Iron overload may cause hemosiderosis
• Symptoms of iron overload include apathy, lethargy, and fatigue

Zinc

• Zinc supports the work of metalloenzymes
• It's involved in DNA and RNA production, heme and hemoglobin synthesis, essential fatty acid metabolism, Vitamin A release from liver stores, and carbohydrate metabolism
• Zinc synthesizes proteins, affects platelets in blood clotting and wound healing, affects thyroid hormone function, influences behavior, learning performance, and taste perception
• Zinc is crucial in sperm development and fetal development
• Zinc absorption depends on the Zinc status in the body and phyates and fiber can reduce Zinc absorption

Zinc Deficiency and Toxicity

• Significant sources: protein-containing foods, red meats, shellfish, and whole grains
• RDA for Zinc: Men - 11 mg/day and Women - 8 mg/day
• Deficiency symptoms: growth retardation, delayed sexual maturation, impaired immune function, hair loss, eye and skin lesions, loss of appetite
• Toxicity symptoms: loss of appetite, impaired immunity, and copper and iron deficiencies

Iodine

• Iodine is a component of two thyroid hormones
• Iodine regulates growth, development, and metabolic rate
• Iodine deficiency leads to simple goiter (enlargement of the thyroid gland)
• Goiter can also result from malfunction of the thyroid, and from overconsumption of goitrogens
• Cretinism is a congenital disease, commonly caused by maternal iodine deficiency during pregnancy
• Iodine toxicity symptoms include underactive thyroid gland and goiter

RDA for Iodine

• RDA for adults: 150 µg/day
• Sources: iodized salt, seafood, bread and dairy products, plants grown in iodine-rich soils, and animals that feed on such plants

Copper

• Copper is a component of many enzymes, and some containing copper are antioxidants
• Copper deficiency can cause anemia and bone abnormalities, including Menkes disease
• Copper toxicity includes Wilson's disease
• RDA for copper in adults is 900 µg/day
• Sources include seafood, nuts, seeds, legumes, and whole grains

Other Trace minerals (Fluoride and Chromium)

• Fluoride - Roles: Formation of teeth and bones, helps make teeth resistant to decay - Deficiency: Tooth decay - Toxicity: Tooth damage (fluorosis) - RDA: Men: 4 mg/day, Women: 3 mg/day - Sources: Fluoridated water, seafood, tea
• Chromium - Roles: Enhances insulin action (through Glucose Tolerance Factors), involved in carbohydrate metabolism - RDA: Men: 35 µg/day, Women: 25 µg/day - Sources : Meat, liver, whole grains, brewer's yeast

Contaminant Minerals (Heavy Metals)

• Contaminant minerals (heavy metals) include mercury, lead, and cadmium
• These enter the food chain through soil, water, and air pollution
• They disrupt body processes and impair nutrition status
• Lead toxicity in children can cause learning disabilities, low IQ, behavior problems, slow growth, iron-deficiency anemia, dental caries, sleep disturbances, nervous system disorders, seizures, slow reaction time, and poor coordination, impaired hearing
• Lead toxicity in adults can cause hypertension and reproductive complications, and kidney failure