Chapter 13
Heme and nonheme iron
2 main types of iron: heme iron = bound to protein (as hemoglobin, myoglobin) -found in animal foods -high bioavailability; 25% absorbed nonheme iron = iron not bound to proteins -found in plant and animal foods; 17% absorbed -ferritin is one form of nonheme iron and is primarily found in legumes; it is better absorbed than other nonheme iron forms such as ferrous sulfate
Iron transport and storage (cont.)
Balance: iron is highly regulated -regulating hormone: hepcidin -produced by liver, maintains iron in blood by controlling absorption and release from storage -hepcidin is decreased in iron deficiency: low levels of hepcidin result in increased iron absorption hepcidin is increased in iron overload: high levels of hepcidin result in decreased iron absorption
Zinc deficiency
Deficiency -widespread in developing world -middle eastern diets inhibit zinc absorption (low in meat, staple foods are phytate-containing foods ... unleavened bread is not fermented with yeast which breaks down phytates) Effects -growth retardation, immature sexual development -promotes malabsorption of other nutrients -impaired immune response -central nervous damage
Selenium deficiency/toxicity
Keshan disease -type of heart disease in regions of China where soil lacks selenium Cancer -may be protective factor -supplements have not proved effective Toxicity -high doses toxic: hair and nail brittleness and loss, nervous system abnormalities
Zinc transport
Recycling -pancreatic secretions are rich in Zn -small intestine receives 2 doses of zinc: 1 from food, 1 from pancreatic enzymes -enteropancreatic circulation of Zn: circulation from small intestines to pancreas, small intestines may reabsorb or Zn in excreted -transport in blood bound to albumin or transferring
Manganese (Mn2+)
Roles in body -cofactor for enzymes that facilitate metabolism -bone formation -conversion of pyruvate to a compound for TCA -defense against oxidative damage: superoxide dismutase in mitochondria
Chromium
Roles in body -participates in carbohydrate and lipid metabolism -helps maintain glucose homeostasis, enhances insulin activity -diabetes-like condition may result if chromium lacking; but supplementing doesn't seem to help Sources -liver, brewer's yeast, whole grains -the more refined foods in diet, the less chromium in diet
Iodine
-GI tract converts iodine in food to iodide (I-); iodide is readily absorbed by the body Roles in body -part of thyroid hormones that regulate: body temp metabolic rate reproduction and growth blood cell production nerve and muscle function
Heme and nonheme iron in foods
-about 40% of the iron in meat/fish/poultry is bound into heme; the other 60% is nonheme iron -heme accounts for about 10% of the avg daily iron intake, but it is well absorbed (about 25%) -nonheme iron accounts for the remaining 90%, but it is less well absorbed (about 17%) -all of the iron in foods derived from plants is nonheme iron
Results from iron deficiency pt. 2
-behavioral symptoms appear before blood is affected -energy metabolism impaired; oxygen needed for metabolic reactions in mitochrondria -neurotransmitter synthesis is altered; reduces work capacity and mental productivity, motivational problems -sometimes misinterpreted as behavioral problems in children
Copper deficiency and toxicity
-deficiency linked to cardiovascular disease in animal studies; not enough research in humans -US diets provide enough intake -excessive intakes (through supplements) may cause liver damage -foods will not result in toxicity
Assessment of iron deficiency
-even small blood losses can cause deficiency -deficiency develops in stages 1. iron stores diminish - serum ferritin 2. decrease in transport iron transferring - low iron but high transferrin circulating 3. hemoglobin and hematocrit values decline
Fluoride
-found in bones and teeth -makes bone, teeth stronger sources -tea and fish -drinking water; benefits = reduces prevalence of dental carries, risks = fluorosis, potential harms such as cancer but limited evidence and poorly conducted studies -fluoride is not in any human pathways
Phytochemicals
-found in plant-derived foods -have biological activity in the body: antioxidant, anti-inflammatory, antimicrobial, mimicking hormones, stimulating enzymes, promoting/suppressing gene expression physiological effects may prevent development of chronic disease -may have adverse effects if consumed in excess
Selenium sources
-found in soil; affects content of fruits and veg -meats, milk, eggs -brazil nuts Recommendations by RDA -amount needed to maximize glutathione peroxidase activity -generally met or exceeded in the US
Iron poisoning
-from larges doses of supplements -nausea, vomiting, diarrhea -rapid heartbeat, shock, confusion -free radical damage may play a role in heart failure/respiratory distress
Iodine deficiency; more severe consequences
-goiter is an early, obvious sign of deficiency -iodine deficiency is the most common preventable cause of mental retardation and brain damage in the world -deficiency during pregnancy = cretinism: congenital disease characterized by mental and physical retardation
Contaminant minerals
-impair body's growth, work capacity, and general health Heavy metals -Lead -indestructible; similar to Fe, Xa, Zn, Cu -displaces nutrient minerals from metabolic sites -children with iron deficiency esp vulnerable Mercury, Cadmium
Assessment of iron deficiency (cont.)
-iron deficiency = low stores but blood is not affected -iron deficiency anemia = depletion of stores that results in low hemoglobin concentration; results in microcytic, hypochromic RBCs, oxygen carrying capacity is compromised -not all anemia is from iron deficiency
Iron sources
-meats, fish, poultry, legumes, eggs -enriched flour and grain products -iron cookware; probably poorly absorbed, acidic foods will accumulate more iron RDA -men of all ages and women over 51: 8mg -women 19-50: 18 mg vegetarians multiply RDA by 1.8 -encourage legumes, veg, nuts, seeds, and absorption enhances like vit C
Iron deficiency*
-most common nutrient deficiency worldwide -associated w/ obesity, esp in children, correlation not understood -possibly due to inflammation interfering with iron absorption **Vulnerable stages in life -women in reproductive years: menstruation -pregnancy: increased demands, increased blood volume, blood loss during childbirth -infants and young children: milk in diet + rapid growth -adolescence: rapid growth, possible poor diet
Iron supplements
-not well absorbed, reason for amounts higher than RDA -usually as ferrous sulfate -best taken on empty stomach or between meals -best absorbed with plenty of water (not not milk/tea) -vit C does not seem to enhance absorption of iron from supplements, ferrous sulfate is already in reduced state -most common GI sympton is constipation but some supplements incorporate a gentle stool softener
Phytochemicals and cancer
-protect against DNA damage -phytoestrogens: found in soy, flax, F&V, whole-grains -antioxidant effects, mimic or modulate estrogen activity -consume soy in moderation lycopene: red/orange F&V -concentrated in tomato products, cooking makes molecule more readily available for absorption -protection against cancer? sulfur-containing molecules: sulforaphane, allicine from cruciferous veg, garlic, onion -antioxidant, anti-inflammatory: cancer-protective properties
Manganese deficiency and sources
-requirements are low, deficiencies are rare -factors that limit manganese absorption: -phytates -high intakes of iron or calcium -toxicity more likely from environmental exposure (mining) than food -sources: grain products, nuts, leafy greens, tea
Selenium
-substitute for sulfur in some amino acids: methionine, cysteine Roles in body -antioxidant -glutathione peroxidase: regenerates oxidized glutathione, prevents oxidative damage from free radicals -enzymes activate or inactivate thyroid hormone
Iodine deficiency
-thyroid hormone production declines with deficiency -increased secretion of thyroid-stimulating hormone (TSH) -cells of thyroid expand: goiter -goiter most often from iodine deficiency -some are dye to excess goitrogen: interfere with thyroid function -food sources: cassava, soy, peanuts, strawberries, cruciferous vegetables
Iron transport and storage
-transferring delivers iron to bone marrow and other tissues storage -ferritin: daily storage, readily accessible -hemosiderin: longer-term storage, slower release -stores when iron is in greater supply -prevents excess iron circulating and acting as a free radical
Copper (Cu2+)
-transport and balance depend on a system of proteins Many roles in the body -constituent of enzymes; reactions that consume oxygen or oxygen radicals -iron metabolism: release of stores, cofactor for hemoglobin synthesis -defends against oxidative damage (along with Zn): superoxide dismutase (SOD) in cytosol -also needed for collagen synthesis
Molybdenum
-working part of several metalloenzymes -dietary deficiencies are unknown sources: legumes, breads, grain products, leafy green veg; widespread -toxicity is rare: kidney damage, reproductive abnormalities
Iodine toxicity and sources
Toxicity -interferes with thyroid function -enlarges thyroid gland; just like deficiency Sources -the ocean: seafood kelp, see salt -iodized salt: 1/2 tsp provides RDA for iodine -iodized salt is used by restaurants and in baking industry but processed foods use regular salt
Zinc toxicity and sources
Toxicity: vomiting, diarrhea, headache -higher doses interfere with copper metabolism; UL set to prevent interference Sources -protein rich foods; shellfish/meats/poultry/milk +cheese Supplementation -zinc lozenges: may shorten duration of common cold
Which of the following is NOT known to affect iron bioavailability? a. caffeine b. phytates c. vit C d. MFP factor
a. caffeine
Enhancing Fe absorption**
absorption-enhances for nonheme iron **MFP Factor = meat, fish, poultry factor -used to be called 'meat effect' -eating spinach (nonheme source) with meat (heme source) enhances absorption bc amino acids bind iron and stabilize it for absorption **Vitamin C -keeps iron in the reduced state (Fe2+) which is better absorbed Some acids and sugars -acts similarily to vit C, stabilize iron so it is better absorbed
Which of the following individuals would most likely NOT need an iron supplement? a. 2 year old b. 55 year old female c. pregnant female d. adolescent female
b. 55 year old female
Which of the following minerals is a cofactor in the formation of hemoglobin? a. iodine b. copper c. selemium d. chromium
b. copper
Iron absorption
body conserves iron -balance maintained primarily through absorption because it is difficult to excrete -more iron is absorbed when stores are empty Ferritin: iron storage in small intestine -if body needs iron, then stores are releaed -if body does not need iron, it will be excreted when the cell is shed (remember, GI tract cells are replaced every 3-5 days) Transferrin: iron transport protein
Which of the following foods are known to contain goitrogens? a. shellfish b. whole grains c. cauliflower and broccoli d. blueberries and raspberries
c. cauliflower and broccoli
Which of the following foods provides the greatest amount of iron per serving? a. yogurt b. skim milk c. pinto beans d. american cheese
c. pinto beans
Which of the following is a major binding protein for zinc? a. ligand b. ferritin c. meosiderin d. metallothionein
d. metallothionein
Which of the following is NOT among the important roles for zinc? a. wound healing b. synthesis of retinal c. production of sperm d. oxidation of polyunsaturated acids
d. oxidation of polyunsaturated acids
Phytochemicals and heart disease
flavonoids: whole-grains, legumes, soy, F&V, herbs, spices, tea, chocolate, nuts, olive oil, red wine -antioxidant properties protect LDL cholesterol from oxidation, minimize inflammation carotenoids: beta-carotene, lutein, lycopene -lowers risk of heart disease and hypertension Lignans: flax and sesame seeds, cruciferous veg -reduce blood cholesterol, anti-inflammatory
Copper sources
food sources: more than 50% Cu in food is absorbed, plant sources possibly less -shellfish -legumes -whole grains -nuts/seeds -water delivered through copper plumbing
Results from iron deficiency
general symptoms -fatigue from exertion, weakness -convave 'spoon' nails -headaches -pallor = pale, unhealthy appearance -pale conjunctiva (lines eyelids) Pica -craving and consumption of nonfood substances -usually ice in large quantities
Copper genetic orders
genetic orders that effect copper status Menkes disease: intestinal cells absorb but don't release Cu; results in life threatening deficiency in rest of the body Wilson's disease: accumulates in brain and liver -can be treated with Zn supplements to interere with Cu absorption -characterized by Kayser-Fleischer ring (eye)
Iron and chronic diseases
heart disease -linked to excess iron -free radicals promote LDL oxidation in arteries; plaque formation cancer -also possibly due to free radical damage (limited evidence)
Iron overload
hereditary hemochromatosis -most common genetic disorder in US -excess iron is absorbed even though it is not needed by the body; most likely related to hepcidin -signs and symptons similar to deficiency: apathy, lethargy, fatigue -don't suggest iron supplements just bc someone feels tired -measure ferritin and transferrin saturation -iron in excess also acts as a free radical -vit C in high doses can act as a prooxidant and release iron from its stores
Iron (Fe3+/Fe2+)
switches back and forth between two forms -Ferrous iron = Fe2+ (reduced state) -Ferric iron = Fe3+ (oxidized state) -cofactor in oxidation-reduction reactions -part of electron carriers in the electron transport chain -most of the body's Fe is in: -hemoglobin: oxygen-carrying protein in RBCs -myoglobin: oxygen-carrying protein in muscle cells
Trace minerals overview
trace mineral contents of foods -vary with soil and water composition, and food processing toxicities -FDA does not regulate trace minerals in supplements; large doses are toxic -do not take supplements with over 100% DV dose
Iron recycled in the body
(see figure) RBC lifecycle is about 120 days; iron is recycled through new generations of RBCs Avg loss for men & women: about 1 mg/day Menstrual loss: about 0.5 mg/day 1. Transferrin carries iron in blood 2. some iron delivered to myoglobin of muscle cells 3. bone marrow incorporates iron into hemoglobin of RBCs and stores excess iron in ferritin (and hemosiderin) 4. iron-containing hemoglobin in RBCs carries oxygen (some losses if bleeding occurs) 5. liver (and spleen) dismantles RBCs, packages iron into transferrin, and stores excess iron in ferritin (and hemosiderin)
Factors that inhibit iron absorption**
**Phylates: legumes, whole-grains -greatest inhibitor -vegetable proteins proteins: soy, nuts -calcium: dairy products -polyphenols: tannic acid in tea, coffee, red wine -dietary factors combined make it difficult to estimate absorption; we estimate that a mixed diet provides about 6g per 1000kcal
Enteropancreatic circulation of zinc
Zinc in food: -mucosal cells in the intestine store excess zinc in metallothionein (If body does not need zinc) -Zinc is not absorbed and it is excreted in shed intestinal cells instead -thus, zinc absorption is reduced when the body does not need zinc (If the body does need zinc) -Metallothionein releases zinc to albumin and transferrin for transport to the rest of the the body -the pancreas uses zinc to make digestiv enzymes and secretes them into the intestine
Zinc absorption
rate varies depending on amount consumed -15-40% percent -rate decreases with increased intake -also affected by phylates -may be used or retained in intestinal cells -retained by important enzyme, metallothionein, until needed -methallothionein stores and transports Zn
Zinc (Zn2+)
required as cofactor for more than 100 enzymes in the body -synthesis of retinal, vit A metabolism -stabilizes cell membranes and DNA -immune function -growth and development -wound healing -synthesis, storage, release of insulin -blood clotting -thyroid hormone function -behavior and learning performance -fertilizer, particularly in sperm production
