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Trace Minerals Lecture 18 Readings: Chapter 13: pages 429 – 453 (Omit “Molybdenum”, “Other Trace Minerals” and “Contaminant Minerals” on pages 450 and 451) Next lectures: Highlights 10, 11, and 13 Overview • trace minerals required only in miniscule amounts • content contained in foods dependant on soil content, water composition, and processing of foods • interactions among trace minerals are common • include: – iron – zinc – iodine – selenium – copper – fluoride – chromium Iron • exists in two forms: – “reduced” or ferrous iron (Fe2+) – “oxidized” or ferric iron (Fe3+) Functions • forms part of electron carriers called ______________ in the electron transport chain • forms part of proteins ________________ and ________________ enabling these proteins to accept, carry and release oxygen • required by enzymes that synthesize collagen, hormones, neurotransmitters, and amino acids Iron Absorption and Metabolism • iron is not readily excreted from the body • iron balance is maintained by adjusting absorption Types of Iron a) _____ • from food derived from animal food sources • 25% absorption b) _________ • from both animal and plant derived foods • only 10% is absorbed Iron Sources Iron Sources Others • broccoli, spinach, dried fruits, eggs, legumes, enriched grains and cereals Contamination Iron • iron found in foods as the result of contamination by inorganic iron salts form iron cookware or iron containing soils Recommendations Men: Women: Iron Factors Enhancing Absorption Factors Inhibiting Absorption Figure 13-1, page 431 Iron Transport and Storage • the intestine absorbs iron and stores it in protein called – iron that is not needed is lost when intestinal cells are shed • when body needs iron, it is moved to another protein called • transferrin transports iron to the rest of the body where it is needed e.g. bone marrow where red blood cells are synthesized Figure 13-1, page 431 Iron Transport and Storage • surplus is stored in ___________ in the liver, bone marrow and spleen • even greater concentrations of iron lead to storage of iron in another protein called ______________ • storage is important to: Iron Deficiency • most common nutrient deficiency world wide • prevalence is higher in less developed countries • greatest risk for women in reproductive years, pregnant women, infants and young children, and teenagers Ways Iron is Lost from the Body… • some iron is lost daily from the digestive tract • only tiny amounts lost through feces, urine, sweat and shedding skin • lost with ___________ Iron Deficiency cont. Stages in the Development of Deficiency 1. – measured by assessing serum ferritin 2. – decreased serum iron – levels of serum transferrin to enhance absorption 3. – insufficient iron to produce hemoglobin – accumulation of erythrocyte protoporphyrin – decrease in hematocrit Iron Deficiency cont. Symptoms a) • red blood cells are small and pale • results in fatigue, weakness, headaches, pallor, poor resistance to cold b) • appear first • unmotivated, apathetic, physically unfit • “pica” = appetite for ice, clay, paste and non-food substances Iron Toxicity • extra dietary consumption generally poses no extra risk because iron absorption decreases when body needs decrease • excess iron is referred to as “iron overload” • hereditary disorder characterized by enhanced iron absorption • results from long-term overconsumption of iron • characterized by deposits of hemosiderin in tissues Iron Toxicity cont. Symptoms & Consequences • tissue damage, deposits of iron • apathy, lethargy and fatigue • increased risk of infections • increased risk of heart disease: – free iron acts as an oxidant – may oxidize LDL and contribute to the development of atherosclerosis • increased risk of cancer – increased free radical formation may contribute to DNA damage • poisoning in children if ingest supplements Zinc Functions • acts as a cofactor for many enzymes Example: • assists in • important for growth and development – required for DNA and RNA synthesis • synthesis of heme in hemoglobin • releases Vitamin A from stores and converts to its active form (retinal) in the retina • forms part of an antioxidant enzyme that protects from free radicals Zinc Functions cont. • stabilizes cell membranes and helps protect them from free radical attack • interacts with platelets in blood clotting • required for the synthesis, storage, and release of the hormone insulin • regulates thyroid hormone function • influences behaviour and learning performance • plays important role in protein synthesis • participates in carbohydrate, fatty acids and alcohol metabolism • others: sperm production, fetal development, taste Zinc Absorption and Metabolism • absorption rate varies between 15 - 40% – dependant on zinc status – absorption inhibited by fibers and phytates • after absorption may be stored by the protein • transported in the blood by two proteins: – albumin – transferrin Zinc Interactions • an excess of dietary iron may reduce zinc absorption – a dietary iron : zinc ratio > 2 : 1 decreases zinc absorption • large doses of zinc: – inhibit iron absorption – interferes with copper absorption Zinc Sources • richest sources are protein rich foods Examples Recommendations Men = 11 mg/day Women = 8 mg/day Zinc Deficiency • most vulnerable are pregnant women, young children, the elderly, and the poor Symptoms • severe growth retardation and arrested sexual development during growth Zinc Deficiency Symptoms cont. • diarrhea • symptoms of a Vitamin A deficiency • impaired thyroid function • altered taste perception • anorexia • impaired glucose tolerance • slowed wound healing • impaired immune function Zinc Toxicity • excessive doses may result in vomiting, diarrhea, headaches • may interfere with ______ and _________ absorption and metabolism Iodine • iodine in foods is converted to its ionic form iodide by the body Functions • an integral part of ________________ • thyroid hormone has many important functions including: – regulation of _______ – regulation of body temperature – necessary for reproduction and growth Iodine Sources • iodized salt, ocean fish, plants grown in iodine rich soil • average intake of North Americans is above recommendation but below toxic levels Iodine Deficiency • results in hypothyroidism and causes an enlargement of the thyroid gland called a ____________ • maternal iodine deficiency during pregnancy leads to _____________ in the developing fetus – affects 6 million people worldwide – characterized by severe physical and mental retardation Iodine Toxicity • also enlarges the thyroid gland causing a __________ • poses risk of suffocation for a fetus is excess consumed during pregnancy – goiter may block airways • upper limit is 1000 mg per day Note • a goiter may also develop from excess consumption of ___________, an anti-thyroid substance found in plants of the cabbage family Selenium Functions • forms part of the enzyme _______________________ – acts as an ___________ Deficiency • associated with a predisposition to a type of heart disease – Keshan disease, also linked to a viral infection • may be associated with an increased incidence of some cancers Toxicity • high doses produce vomiting, diarrhea, hair loss, skin lesions and neurological problems Copper Functions • forms part of several enzymes including __________ ______________ – an _________________ • important for the synthesis of ____________ Sources • legumes, whole grains, nuts, shellfish, organ meats, seeds, water Copper Deficiency • rare, may be associated with excess Vitamin C which interferes with absorption • symptoms include _________________ • in animals leads to increased blood cholesterol and damage to blood vessels Toxicity • rare • may interfere with iron and zinc metabolism Fluoride Functions • forms ____________________ in teeth – replaces the hydroxyl (OH) in hydroxyapatite crystals Deficiency • associated with _____________ • _______________________________ confers best protection against dental caries • primary source of fluoride is drinking water; also in tea and seafood Fluoride Toxicity • ____________ – damage to teeth that pits and stains the enamel • also leads to nausea, vomiting, diarrhea, chest pain, and itching Chromium Functions • regulates carbohydrate and lipid metabolism • enhances _______________ Sources • present in a wide variety of foods • rich sources include liver, brewer’s yeast, whole grains, nuts and seeds Deficiency • produces a ____________________ marked by an inability to use glucose normally