Classification of Minerals

1/1/2019 Classification of minerals — Minerals represent approximately 4% to 5% of body weight — The mineral nutrients most are traditionally divided into: — Macrominerals (major minerals): ≥ 100mg/day required — Microminerals or trace elements (minor minerals) : (<15 mg/ day required). 4 5 2 1/1/2019 15 Microminerals — Microminerals are required less than 20 mg/day — Nine essential trace elements: § Iron, manganese, molybdenum, selenium, zinc, and fluoride, chromium, copper, iodine, 16 3 1/1/2019 Iron — Iron has been recognized as an essential nutrient for more than a century. — Iron-deficiency anemia is the world's most common nutritional deficiency disease. — The adult human body contains iron in two major pools: • (1) functional iron in hemoglobin, myoglobin, and enzymes • (2) storage iron in ferritin, hemosiderin, and transferrin. vHealthy adult men have approximately 3.6 g of total body iron, v whereas women have approximately 2.4 g 23 Iron — Adult women store lower amounts of iron than do men. — Iron is highly conserved: § approximately 90% is recovered and reused every day § the rest is excreted, primarily in bile. vIf dietary iron is not available to meet this 10% gap, iron deficiency results. 25 4 1/1/2019 27 Two concerns about iron nutritional status § the incidence of iron-deficiency anemia § the role of excessive iron intake in coronary heart disease and cancer. v Because of food fortification and the use of iron supplements by so many individuals, high iron intakes by men and postmenopausal women may be contributing to the risk of these chronic diseases. 28 5 1/1/2019 Iron Absorption — Dietary iron exists as : — heme iron: § found in hemoglobin, myoglobin, and some enzymes — nonheme iron: § § found predominantly in plant foods, but also in some animal foods as nonheme enzymes and ferritin. 29 30 6 1/1/2019 Heme Iron Absorption — Heme iron is digested from animal sources. — It is absorbed across the brush border of intestinal absorbing cells. — The ferrous iron is enzymatically removed from the ferroporphyrin complex. — The free iron ions combine immediately with apoferritin. — Ferritin is an intracellular store, a "ferry" that carries bound iron from the brush border to the basolateral membrane of the absorbing cell. — The final step of absorption by which iron ions are moved into the blood involves an active transport mechanism. 32 Figure 3-22 33 7 1/1/2019 34 Heme Iron Absorption (cont.) — The absorption of heme iron is affected only minimally by the composition of meals and GI secretions. — Heme iron represents only 5% to 10% of the dietary iron in a mixed diet, — absorption may be as high as 25%, § compared with only 5% for nonheme iron. v Because vegans consume only plant foods, sufficient amounts of nonheme iron must be ingested and absorbed to meet body requirements or supplements would be needed. 35 8 1/1/2019 Non-Heme Iron Absorption qNonheme iron must be digested from food sources. qThe acid of gastric secretions enhances the solubility and changes iron to the ionic state-either as ferric (+3 oxidation state) or ferrous (+2 oxidation state) iron-within the gut luminal contents. qIron in the reduced, ferrous state is preferred for the entry step of absorption. § Ferric iron may be reduced by a brush border enzyme, ferric reductase, for absorption. qThe brush border iron transporter, divalent metal transporter 1 (DMT1), transports ferrous iron. vIron is absorbed in duodenum and upper jejunum. 37 41 9 1/1/2019 43 Iron absorption 44 10 1/1/2019 Control of Iron Absorption q The efficiency of nonheme iron absorption seems to be controlled by the intestinal mucosa, which allows certain amounts of iron to enter the blood from the cytosolic ferritin pool according to the body's needs. § A small peptide hormone known as hepcidin is the main iron regulatory hormone. q Hepcidin production in the liver is responsive to : § liver iron levels § inflammation § hypoxia § anemia. q Hepcidin major action is to act on the mucosa cell and inhibit iron absorption. 45 Control of Iron Absorption (cont.) — Other signals from the body to the absorbing cells may be transferrin saturation, or the percentage of iron bound to transferrin § Normally transferrin saturation is 30% to 35% in healthy, iron-consuming individuals. § The percentage can vary greatly, depending on iron intake and bioavailability. § A low percentage (e.g., 15%) of the total iron-binding capacity (TIBC) of transferrin would stimulate the absorbing cells to transport iron by the exit step at the basolateral membrane to the blood. § Conversely, if the iron concentration in the body is excessive, absorbing cells would be down regulated, and less iron would be absorbed. § The latter situation occurs during iron overloads to protect the body against toxicity. 46 11 1/1/2019 The efficiency of iron absorption — In individuals who persistently consume inadequate levels of iron, especially — — — — — women in their childbearing years, the number of receptors may consistently be upregulated to maximize iron absorption. The efficiency of iron absorption by adults with normal hemoglobin values averages 5% to 15% of the iron, heme and nonheme, from food and supplements. Although absorption may be as high as 50% in those with iron deficiency anemia, this level is not common. Most women with an iron deficiency, but not anemia, probably have absorption efficiencies of 20% to 30%. From 2% to 10% of nonheme iron in vegetables is absorbed, from 10% to 30% of iron heme and nonheme from animal sources is typically absorbed. 48 Several factors affect the intestinal absorption of iron — Ascorbic acid, the most potent enhancer of iron absorption; § reduces ferric to ferrous iron § forms a chelate with iron that remains soluble at the alkaline pH of the lower small intestine. — Other food molecules, such as sugars and sulfur-containing amino acids, may also enhance iron entry by: § forming chelates with ionic iron. — animal proteins from beef, lamb, liver, fish, and chicken enhance absorption. § The substance responsible for this improved absorption-the meat-fish-poultry (MFP) factor-remains unknown, but specific amino acids or dipeptide digestion products may enhance iron absorption. 49 12 1/1/2019 Several factors affect the intestinal absorption of iron (cont.) — Although the iron content of human milk is very low, — it is highly bioavailable because of the presence of milk lactoferrin, which enhances iron absorption. — Infants retain more iron from human milk than from cow's milk or infant formulas because of the presence of lactoferrin in breast milk. — Whey protein (lactalbumin), which constitutes a greater percentage of the total protein in human milk than in cow's milk, may also improve iron absorption. 50 Several factors affect the intestinal absorption of iron (cont.) — The degree of gastric acidity enhances solubility and therefore bioavailability of iron derived from foods. § Therefore achlorhydria, hypochlorhydria, or administration of alkaline substances such as antacids can interfere with nonheme iron absorption • by not permitting the solubilization of iron in gastric and duodenal fluids. — Gastric secretions also seem to increase the absorption of heme iron. 51 13 1/1/2019 Several factors affect the intestinal absorption of iron (cont.) — Certain physiologic states such as pregnancy and growth that involve increased blood formation stimulate iron absorption. — In addition, more iron is absorbed during iron deficiency states because of adaptive mechanisms that enhance nonheme iron absorption. 52 Iron absorption decreases by: — Foods with high phytate content have low iron bioavailability, but whether phytate is the cause is not clear. — Oxalates can inhibit absorption. — Tannins, which are polyphenols, in tea also reduce nonheme iron absorption. — 53 14 1/1/2019 Several factors affect the intestinal absorption of iron (cont.) — the presence of an adequate amount of calcium helps to: § remove phosphate, oxalate, and phytate § that would otherwise combine with iron and inhibit its absorption. 54 55 15 1/1/2019 Iron absorption: — Pathologic states: — Hypoxia, anemia, inflammation, Iron deficiency — Physiologic sates § Iiver Iron levels, body needs, pregnancy, TIBC saturation — Enhancers and inhibitors of absorption — Hem/nonheme Iron and Iron compound 57 58 16 1/1/2019 59 60 17 1/1/2019 IronTransport — Iron (nonheme) is transported: § bound to transferrin from the intestinal absorbing cells to various tissues to meet their needs. § It rarely exists in the free ionic state in serum. 62 Iron Storage — Between 200 and l500 mg of iron is stored in the body : § as ferritin and hemosiderin • 30% is in the liver • 30% is in the bone marrow • and the rest is in the spleen and muscles. — Up to 50 mg/day can be mobilized from storage iron: § 20 mg of which is used in hemoglobin synthesis — The amounts of circulating ferritin in blood correlate closely with total body iron stores, which makes this measurement valuable for evaluation of iron status. 64 18 1/1/2019 Excretion — Iron is lost from the body only through: § bleeding § and in very small amounts through defecation, sweat, and the normal exfoliation of hair and skin. v Most of the iron lost in the feces could not be absorbed from food. The remainder comes from bile and the cells exfoliated from the GI epithelium. vAlmost no iron is excreted in the urine. vDaily iron loss is approximately 1 mg . 65 66 19 1/1/2019 Iron Function — The functions of iron relate to its ability to participate in oxidation and reduction reactions. — Chemically, iron is a highly reactive element that can interact with oxygen to form intermediates with the potential of damaging cell membranes or degrading DNA. — Iron must be tightly bound to proteins to prevent these potentially destructive oxidative effects. 67 68 20 1/1/2019 Iron Function — Hemoglobin in the blood carries oxygen from the lungs to tissues throughout the body. — Myoglobin holds oxygen for the muscles to use when they contract. — As part of many enzymes, iron is vital to the processes by which cells generate energy. — Iron is also needed to make new cells, amino acids, hormones, and neurotransmitters. 69 An adequate iron intake is especially important qWomen are especially prone to iron deficiency during their reproductive years. qPregnancy places further iron demands on women: § iron is needed to support the added blood volume, the growth of the fetus, and blood loss during childbirth. q Infants (6 months or older) and young children receive little iron from their high-milk diets, yet they need extra iron to support their rapid growth and brain development. q The rapid growth of adolescence, especially for males, and the blood losses of menstruation for females also demand extra iron that a typical teen diet may not provide. 70 21 1/1/2019 Causes of Iron Deficiency — The cause of iron deficiency is usually inadequate intake resulting from iron-poor food choices . — Blood loss is the primary nonnutritional cause, especially in poor regions of the world where parasitic infections of the GI tract may lead to blood loss. 71 Stages of iron deficiency qFirst stage : qnegative iron balance (i.e., iron depletion). — In these stages iron stores are low and there is no dysfunction. — Serum ferritin ↓ 72 22 1/1/2019 Stages of iron deficiency (cont.) qSecond stage : qinadequate body iron — Transferrin ↑ — Serum Iron↓ 73 Stages of iron deficiency (cont.) qThird stage : qHb ↓, Hct ↓ qIron deficiency anemia 74 23 1/1/2019 Iron deficiency q Less severe iron deficiency : — ↓physical work capacity — ↓mental productivity — unmotivated, apathetic — Children :irritable, restless, and unable to pay attention q severe depletion of iron stores: — Microcytic hypochromic anemia — fatigue, weakness, headaches, apathy, pallor, and poor resistance, to cold temperatures. 75 Iron Deficiency and Pica — Pica is the craving for and consumption of ice, chalk, starch, and other nonfood substances. — It is seen in some iron-deficient (and sometimes zinc-deficient) people, especially in women and children of low-income groups. — These substances contain no iron and cannot remedy a deficiency; — Clay actually inhibits iron absorption, which may explain the iron deficiency that accompanies such behavior. — Researchers hypothesize that it may be motivated by hunger, nutrient deficiencies, or an attempt to protect against toxins or microbes 76 24 1/1/2019 Caution on Self-Diagnosis — Low hemoglobin may be due to other nutrient deficiency, disease, or agent that interferes with hemoglobin synthesis, disrupts hemoglobin function, or causes a loss of red blood cells. — Thus, feeling fatigued, weak, and apathetic is a sign that something is wrong and that a person should consult a physician, not an indication that he or she should take supplements. — In fact, iron supplements can mask a serious medical condition, such as hidden bleeding from cancer or an ulcer. — Furthermore, a person can waste precious time by not — seeking treatment. Remember, don’t self-diagnose. 77 Iron Overload — Iron levels in the body are closely regulated and absorption normally decreases when iron stores are full. — Iron overload, known as hemochromatosis, is usually caused by a genetic failure to prevent unneeded iron in the diet from being absorbed. — A deficiency of or (rarely) resistance to hepcidin causes hemochromatosis. — Other causes of iron overload include repeated blood transfusions, massive doses of supplementary iron, and other rare metabolic disorders. 78 25 1/1/2019 Signs and symptoms of iron overload — are similar to those of iron deficiency: apathy, lethargy, and fatigue. — Iron overload assessment tests measure transferrin saturation and serum — — — — — ferritin. Iron overload is characterized by free-radical tissue damage, especially in ironstoring organs such as the liver. Infections are likely because bacteria thrive on iron-rich blood. Untreated hemochromatosis aggravates the risk of diabetes, liver cancer, heart disease, and arthritis. Iron overload is much more common in men than in women and is twice as prevalent among men as iron deficiency. 79 Iron Poisoning — The rapid ingestion of massive amounts of iron can cause sudden death. — Iron-containing supplements can easily cause accidental poisonings in young children. 80 26 1/1/2019 Dietary Reference Intakes — The RDA for men and postmenopausal women is 8 mg/day. — The RDA for women of childbearing age (to replace iron loss from menstruation and provide for iron stores sufficient to support a pregnancy) is 18 mg/day. — For teenage boys (ages 14 to 18) the iron RDA is 11 mg/day. — 90 Food Sources and Intakes — The best source of dietary iron is § liver, followed by seafood, kidney, heart, lean meat, and poultry. — Dried beans and vegetables are the best plant sources. — Some other foods that provide iron are egg yolks, dried fruits, dark molasses, whole-grain and enriched breads, wine, and cereal. vOld fashioned iron skillets used for cooking add to the total iron intake.. 92 27