Notes on Trace Minerals

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Food Science and Human Nutrition
HUN 2201
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HUN 2201 – Trace Minerals • Interactions affect bioavailability • Iron o Iron-containing protein hemoglobin. Deficiency of iron decreases hemoglobin production • Iron in the Diet o Comes from plant and animal sources o Animal iron: heme iron  Found in hemoglobin in blood and myoglobin in muscle  Meat, poultry, fish  10-15% dietary iron in meat eaters o Plant iron: nonheme  Leafy greens, legumes, whole and enriched grains  Iron from cooking utensils leaches into acidic foods • Iron in the Digestive Tract o Absorbed into intestinal mucosal cells o Heme absorbed more efficiently than nonheme, not affected by factors that affect nonheme absorption  When foods containing heme proteins are consumed, iron-containing heme group released by protein digesting enzymes. Heme binds to receptors on surface of mucosal cells, where iron is released.  When foods containing nonheme iron are consumed, stomach acid converts ferric to ferrous, which is more soluble. Absorption enhanced by acid, maintains ferrous form. Meat can also enhance nonheme absorption • Dietary factors that interfere with absorption include fiber, phytates in cereal, tannins in tea, oxalates in spinach. Bind to iron in GI tract. Calcium consumed in the same meal decreases absorption. • Iron in the body o How iron homeostasis is regulated  Controlled at intestine  Increased hepcidin leads to anemia, since it inhibits iron release , decreased hepcidin produces iron overload  Iron in mucosal cells can be bound to storage protein ferritin (excreted in feces) or transferred into blood and picked up by iron transport protein transferrin (to liver, bones, tissues) • Iron converted to ferric form by copper-containing protein before it binds to transferrin  Amount of iron transported from mucosal cells to the rest of the body depends on iron needs • Regulated by hepicidin, released by the liver. When body iron is low, little hepicidin is released, allowing intestinal mucosal cells to transfer iron into the blood, where it binds to transferrin. High levels of iron cause hepcidin release, which inhibits iron from being released into the blood when bound to ferritin in body cells such as liver cells and macrophages  Iron losses and recycling • No physiological mechanism for regulating iron losses o Most occurs through blood loss and shedding of cells from intestine, skin, and urinary tract o When cells die, iron is recovered and attached to transferrin for transport back to body tissues • Iron stores o When transported from mucosal cells into blood in excess of needs, can be stored in protein ferritin [liver, spleen, bone marrow] o High ferritin concentrations cause some to be converted into insoluble storage protein hemosiderin • How iron functions in the body o Oxygen-carrying proteins hemoglobin and myoglobin o Essential for ATP production, immune function, drug metabolism, and part of enzyme catalase that functions as antioxidant  Iron deficiency • Most common • No hemoglobin produced; microcytic and hypochromic anemia = last stage of iron deficiency o Symptoms include fatigue, headache, inability to maintain body temp, changes in behavior, decreased immunity, adverse pregnancy and fetal development, and increased risk of lead poisoning o Adolescents, toddlers and women, especially minorities o Athletes at risk as well, EAR may be higher o Separate RDA for menstruating women, pregnant women, and vegetarians  Iron toxicity • PROMOTES FORMATION OF FREE RADICALS AND CAUSES EXCESS OXIDATION OF CELLULAR COMPONENTS. Can be acute or chronic [iron overload] • Acute toxicity o Single large dose can damage intestinal lining and cause changes in blood pH, shock, and liver failure • Iron overload o Accumulation in tissues, abnormal red blood cell synthesis o Most common cause is hemochromatosis  Inherited, caused by defect in gene for hepicidin, common in Caucasians  Symptoms appear in middle age, weight loss, fatigue, abdominal pain, then heart and liver damage, diabetes, cancer, darkening skin  Recessive gene, but people with one allele absorb iron better than those who don’t have the gene o Rate at which iron accumulates depends on amount consumed and other factors such as menstruation and blood donations o Regular blood withdrawl is treatment option o People with high iron stores are at risk for some of the same problems that occur with hemochromatosis o Can promote heart disease by increasing formation of LDL cholesterol, and can promote diabetes because it promotes formation of free radicals, which contributes to insulin resistance and eventually decreased insulin secretion.  Supplements NOT recommended for adult men and postmenopausal women • Meeting iron needs o Red and organ meats, although good nonheme sources include legumes, dried fruit, leafy greens, and fortified grain products. o fed vitamin C and decreased dairy promotes absorption o Ferrous form in supplements better absorbed than ferric  Zinc • Absorption hindered by phylates • Zinc in the diet o Both plant and animal sources o Animal sources are better; red eat, liver, eggs, dairy, veggies, some seafood, whole grains o Refine grains are POOR source, not added back in enrichment. Products leavened with yeast are better than unleavened because yeast reduces the phytate content • Zinc in the digestive tract o GI tract is major site for regulation of homeostasis o Zinc transport proteins regulate the amount of zinc in the cytosol of the mucosal cells  Promote transport of zinc from lumen into cells, and reduce amount of zinc in cytool by transporting zinc back into lumen or into storage vesicles  Regulated by increased/decreased production of zinc transport proteins o Amount of zinc that passes from mucosal cell into the blood Is also regulated by metal-binding protein metallothionein  Synthesis increases when zinc is high, slows transfer into the blood. Also, binds copper..high levels can inhibit copper absorption • Zinc in the body o MOST ABUNDANT INTRACELLULAR TRAE ELEMENT o INCYTOSOL, ORGANELLES, NUCLEUS, pancreatic and intestinal juices o When zinc levels in the body are low, zinc in GI tract can be absorbed and recycled. When levels are high, more is eliminated in the feces • How zinc functions in enzymatic reactions o Involved in functioning of enzymes such as superoxide Dismutase SOD  Vital for protecting cells from free radical damage  Needed to maintain levels of metallothionein, which also scavenge free radicals  Essential for activity of enzymes that function in synthesis of proteins, DNA, RNA, in carb metabolism, pH balance, and reaction that is necessary for the absorption of folate from food  Plays a role in the storage and release of insuling, and the mobilization of vitamin A from the liver, stabilization of cel membranes  Influences hormonal regulation of cell division and needed for growth/repair of tissues, immunity, and development of sex organs and bone • How zinc regulates gene expression o Binds to regulatory factor and activates transcription o Proteins containing zinc fold around the zinc atom to form a loop, allowing nuclear receptor proteins to bind to regulatory regions on DNA, stimulating the transcription of specific genes and therefore the synthesis of the proteins for which they code o Without zinc, certain vitamins and hormones cannot interact with DNA to increase or decrease gene expression and synthesis of certain proteins  Zinc deficiency • Seen in individuals with acrodermatitis enteropathica, in those fed total parenteral nutrition solutions lacking zinc, and in consuming diets low in protein and high in phytates, individuals with kidney disease, sickle cell anemia, alcoholism, cancer, or AIDS • Symptoms: o Poor growth and development, skin rashes, hair loss, diarrhea, neurological changes, inpaired reproduction, skeletal abnormalities, reduced immune function o Uncommon in north America due to supplements and fortified foods o Common in pregnant women, elderly, and vegans  Recommended Zinc intake • RDA INCREASED DURING LACTATION AND PREGNANCY  Zinc Toxicity • Gi IRRITATION, VOMITING, LOSS OF APPETITE, DIARRHEA, CRAMPS, HEADACHES • Can decrease immune function, reduce HDL [good cholesterol], interfere with copper absorption  Zinc supplements • MARKETED AS A SUPPLEMENT TO IMPROVE IMMUNE FUNCTION AND FERTILITY, SEXUAL PERFORMANCE • No evidence, although mildsupplementation can improve wound healing, immunity, and appetite, and in children, growth and learning. Genetic diseases  Do zinc lozenges relieve cold symptoms? • Evidence is mostly in support, although overdose can cause GI issues and oral irritation • Too much zinc can also suppress the immune system, lower HDL cholesterol, and impair copper absorption  Supplemental Zinc to Treat Genetic Disorders • Acrodermatitis enteropathica: inherited defect in absorption that results in zinc deficiency o Causes skin lesions, eye damage, increased risk of infection o Can be treated with high levels of zinc, patients just must be monitored to ensure that they don’t suffer copper deficiency • Wilson’s disease: inherited defect in excretion of copper, which accumulates in the body o Supplemental zinc acetate blocks absorption of copper and increase excretion in the stool • Copper o Can treat certain types of anemia o Menkes disease or kinky hair disease: defect in intestinal copper absorption o Copper in the diet  Organ meats [liver and kidney]  Seafood, nuts and seeds, whole grains, chocolate  Soil content affects food content in plants o Copper in the digestive tract  30-40% in diet is absorbed, affected by presence of other minerals in the diet • High zinc content stimulates synthesis of metallothionein in mucosal cells • Metallothionein binds copper and prevents it from leaving mucosal cells, so phytates increase absorption and utilization of copper • Copper absorption also reduced by high intakes of iron, manganese, molybdenum, vitamin C, antacids o How copper functions in the body  Binds to albumin in blood and travels to liver, where it binds to ceruloplasmin • Must be transported bound to these proteins because free copper ions can trigger oxidation and cellular damage  Can be removed in bile and feces  Functions in i
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