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272
Chapter 13 – The Trace Minerals
Learning Objectives
After completing Chapter 13, the student will be able to:
1. Identify the functions of iron in the body.
2. Identify factors that increase and decrease iron absorption from the diet.
3. Describe the transport and storage of iron in the body.
4. Discuss populations at risk for iron deficiency and identify symptoms of iron deficiency and iron toxicity.
11. Identify food sources of iodine and the impact of iodization of salt.
12. Describe the uses of selenium in the body and the role of selenium in cancer protection.
13. Identify food sources of selenium and the amount needed daily.
14. Describe the role of copper in the body and major food sources of copper.
15. Describe the role of manganese in the body and the major sources of the trace mineral.
16. Explain the uses of fluoride in the body and its role in dental caries prevention.
Assignments and Other Instructional Materials
The following ready-to-use assignments are available in this chapter of the instructor’s manual:
• New! Case study
• Worksheet 13-1: Beyond the Goiter Belt1
Other instructional materials in this chapter of the instructor’s manual include:
• Answer key for How To (p. 432) activity
• Classroom activities
• Worksheet answer keys (as appropriate)
1 Worksheets 13-1, 13-2, and 13-4 contributed by Daryle Wane.
2 Contributed by Mary A. Wyandt, Ph.D., CHES
3 Handouts 13-1 and 13-2 contributed by Sharon Rady Rolfes
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Lecture Presentation Outline4
“Of special interest to...” symbol key: = Hot Topic = Personal Health
= Health Care Professionals = Science Majors
Key to instructor resource annotations (shown to the right of or below outline topics):
PL = Available on Power Lecture DVD-ROM (ISBN 0538797592): V = video
TRA = Transparency acetates: 12e TRA = 12th edition, 11e TRA = 11th edition, 10e TRA = 10th edition
I. The Trace Minerals—An Overview IM CI 13.1, 13.2
Trace minerals are needed in very small quantities in the human body. They perform many essential functions
important to health. Toxic levels can easily be reached with the use of supplements. Humans can get the
amounts of trace minerals needed by consuming a wide variety of foods.
A. Food Sources
1. Depends on soil and water composition.
B. Deficiencies
1. Severe deficiencies of some minerals are easy to recognize, while others can be difficult to diagnose.
2. Mild deficiencies are easily overlooked.
4. Deficiencies affect all ages, but in children, they can affect growth.
C. Toxicities 12e TRA 19
1. Do not exceed Tolerable Upper Intake Levels.
2. FDA does not limit amounts in supplements.
II. Iron
Iron is an essential nutrient found in the body as a part of hemoglobin and myoglobin. Iron is used for energy
metabolism and enzyme activity. Special proteins assist with iron absorption, transport, and storage. Both iron
deficiency and iron toxicity cause damage, so balance is important. Heme iron is better absorbed but nonheme
iron absorption can be enhanced.
A. Iron Roles in the Body
1. Ferrous iron is reduced and has a net positive charge of two.
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B. Iron Absorption and Metabolism 10e TRA 140
1. Iron Absorption
a. The protein ferritin stores iron in the mucosal cells lining the digestive tract.
2. Heme and Nonheme Iron 10e TRA 141
a. Heme iron
1. Found in foods that are from the flesh of animals (meat, poultry, and fish).
2. Represents only 10% of a day’s iron consumption, but has an absorption rate of 25%.
3. Absorption-Enhancing Factors
4. Absorption-Inhibiting Factors
a. Phytates from legumes, whole grains, and rice.
5. Dietary Factors Combined
6. Individual Variation
a. Dietary factors.
7. Iron Transport and Storage
a. Surplus is stored in bone marrow, spleen, and liver.
b. Hemosiderin is a storage protein used when concentrations of iron are extremely high.
c. Storing excess iron is a protective measure because iron can act as a free radical.
8. Iron Recycling 10e TRA 142
a. The liver and spleen dismantle red blood cells and package iron into transferrin.
9. Iron Balance
a. The absorption, transport, storage, recycling, and loss of iron must be regulated in order to
maintain iron balance.
b. Hepcidin is a hormone that inhibits the absorption and transport of iron to keep blood levels
within normal ranges.
C. Iron deficiency is the most common nutrient deficiency. 10e TRA 143; IM CI 13.3
1. Symptoms
a. Anemia: weakness, fatigue, headaches, and impaired work and cognitive performance.
2. Vulnerable Stages of Life – Iron-deficiency anemia can affect individuals in many stages of life.
a. Women in reproductive years due to menstruation.
3. Blood Losses
a. Can be from non-obvious sources such as a bleeding ulcer.
4. Assessment of Iron Deficiency
a. Stage 1 is when iron stores diminish and is measured by serum ferritin levels.
5. Iron Deficiency and Anemia
6. Iron Deficiency and Behavior
a. Energy metabolism is impaired.
7. Iron Deficiency and Pica
a. Generally found in women and children from low-income groups.
b. Eating ice, chalk, starch, and other nonfood substances.
c. Eating nonfood substances will not correct the deficiency.
D. Iron Toxicity
1. Iron Overload IM WS 13-2
a. Hemochromatosis is generally a genetic disorder that enhances iron absorption and may be
caused by a lack of hepcidin.
b. Iron overload can also be caused by:
1. Repeated blood transfusions.
2. Massive doses of supplemental iron.
h. Treated with chelation therapy.
2. Iron and Heart Disease – may be a link to high iron stores.
3. Iron and Cancer – may be a link with free radical activity resulting in damage to DNA.
4. Iron Poisoning
a. UL for adults: 45 mg/day.
b. Accidental supplement poisoning in children.
c. Symptoms include nausea, vomiting, diarrhea, rapid heartbeat, weak pulse, dizziness, shock, and
confusion.
E. Iron Recommendations and Sources
1. Recommended Iron Intakes
a. RDA Men: 8 mg/day for adults 19-50 years of age.
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d. Vegetarians need 1.8 times as much iron because of low bioavailability.
2. Iron in Foods 10e TRA 144
a. Red meats, fish, poultry, and shellfish.
3. Iron-Enriched Foods
4. Maximizing Iron Absorption
a. Bioavailability is high in meats, fish, and poultry.
d. Combined effect of enhancing and inhibiting factors.
F. Iron Contamination and Supplementation
1. Contamination Iron
2. Iron Supplements
a. Best absorbable form is ferrous sulfate or an iron chelate.
b. Take on empty stomach and with liquids other than milk, tea, or coffee.
III. Zinc
Zinc is important in a multitude of chemical reactions in the body. The best sources of dietary zinc are protein-
rich foods. Zinc from pancreatic secretions is also available for absorption. Phytates and fiber can bind zinc,
therefore limiting absorption. A special binding protein monitors the absorption of zinc. Zinc deficiency
symptoms include growth retardation and sexual immaturity.
A. Zinc Roles in the Body
1. Supports the work of metalloenzymes.
a. Helps to make parts of DNA and RNA.
b. Manufactures heme for hemoglobin.
2. Involved in growth, development, and immune function.
3. Affects platelets in blood clotting and wound healing.
4. Needed to produce the retinal form of vitamin A.
5. Affects thyroid hormone function.
B. Zinc Absorption and Metabolism
1. Zinc Absorption
a. Rate of absorption depends on zinc status; when more is needed, more will be absorbed.
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c. Metallothionein is a special protein that holds zinc in storage.
2. Zinc Recycling 10e TRA 145
C. Zinc Deficiency
1. Not widespread.
2. Occurs in pregnant women, young children, the elderly, and the poor.
3. Symptoms of deficiency
a. Growth retardation.
D. Zinc Toxicity
1. UL for Adults: 40 mg/day.
2. Symptoms
a. Loss of appetite.
b. Impaired immunity.
E. Zinc Recommendations and Sources
1. Recommended intakes
a. RDA Men: 11 mg/day.
b. RDA Women: 8 mg/day.
2. Zinc in foods 10e TRA 146
a. Protein-containing foods such as shellfish, meats, poultry, milk, and cheese.
IV. Iodine
Iodide is an essential component of the thyroid hormone that helps to regulate metabolism. Iodine deficiency
can cause simple goiter and cretinism. The iodization of salt has greatly reduced iodine deficiency in the United
States and Canada.
A. Iodide Roles in the Body
1. Component of two thyroid hormones (T3 and T4).
2. Regulates body temperature, growth, development, metabolic rate, nerve and muscle function,
rutabaga, soybeans, peanuts, peaches, and strawberries.
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3. Cretinism is a congenital disease characterized by mental and physical retardation and commonly
caused by maternal iodine deficiency during pregnancy.
C. Iodine Toxicity
1. UL 1100 g/day.
e. Animals that feed on plants grown in iodine-rich soils.
V. Selenium
Selenium is an antioxidant nutrient associated with protein foods. It may provide some protection against
certain types of cancer.
A. Selenium Roles in the Body
1. Defends against oxidation.
2. Regulates thyroid hormone.
3. Food sources are better than supplements.
D. Selenium Recommendations and Sources
1. Recommendations – Adults: 55 g/day.
2. Sources include seafood, meat, whole grains, and vegetables (depends on soil content).
E. Selenium Toxicity
1. UL for Adults: 400 g/day.
2. Symptoms
VI. Copper
Copper is a component of several enzymes associated with oxygen or oxidation. Copper deficiency is rare.
There are some diseases associated with excessive intakes. Food sources of copper include legumes, whole
grains, and seafood.
A. Copper Roles in the Body
1. Absorption and use of iron in the formation of hemoglobin.
B. Copper Deficiency and Toxicity
1. Deficiency is rare in the U.S.; however, symptoms include anemia and bone abnormalities.
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c. Excessive intake from supplements can cause liver damage.
C. Copper Recommendations and Sources
1. Recommendations – Adults: 900 g/day.
VII. Manganese
Manganese is a cofactor for several enzymes involved in bone formation and various metabolic processes.
Deficiencies are rare and toxicities are associated with environmental contamination. Manganese is found in
many foods.
A. Manganese Roles in the Body
1. Cofactor for several enzymes.
2. Assists in bone formation.
3. Pyruvate conversion.
B. Manganese Deficiency and Toxicity
1. Deficiency symptoms are rare.
5. Toxicity symptoms include nervous system disorders.
C. Manganese Recommendations and Sources
1. Recommendations
a. AI Men: 2.3 mg/day.
VIII. Fluoride
Fluoride makes bones stronger and teeth more resistant to decay. A deficiency of fluoride increases
susceptibility to tooth decay. The use of fluoridated water can reduce dental caries. Excess fluoride causes
fluorosis—the pitting and discoloration of teeth.
A. Fluoride Roles in the Body
1. Formation of teeth and bones.
b. Leads to nutritional problems due to issues with chewing.
B. Fluoride and Toxicity
1. Tooth damage called fluorosis – irreversible pitting and discoloration of the teeth.
2. UL for Adults: 10 mg/day.
3. Prevention of fluorosis
a. Monitor fluoride content of local water supply.
C. Fluoride Recommendations and Sources
1. Recommendations
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IX. Chromium
Chromium is an essential nutrient that enhances insulin’s action. It is widely available in unrefined foods. A
deficiency of chromium can result in the development of a diabetes-like condition. There are no reported
toxicities.
A. Chromium Roles in the Body
1. Enhances insulin action and may improve glucose tolerance.
B. Chromium Recommendations and Sources
1. Recommendations
a. AI Men: 35 g/day.
X. Molybdenum
Molybdenum is a cofactor in several enzymes. It is needed in minuscule amounts. It is available in legumes,
grains, and organ meats.
A. Molybdenum functions as a cofactor for several enzymes.
B. No known deficiency symptoms.
XI. Other Trace Minerals
Much of the research on other trace minerals is from animal studies. Humans need very small amounts.
Determining exact needs, functions, deficiencies, and toxicities is difficult. Some key roles of these other trace
minerals have been identified.
A. Nickel is a cofactor for certain enzymes.
XII. Contaminant Minerals
Contaminate minerals are also called heavy metals. These include mercury, lead, and cadmium. These minerals
enter the food supply through soil, water, and air pollution. They disrupt body processes and impair nutrition
status.
A. Lead can have a severe impact on growth and development.
B. Lead interferes with other nutrients.
XIII. Highlight: Phytochemicals and Functional Foods IM WS 13-4, CI Highlight
Phytochemicals are nonnutrient compounds. Only a few of the thousands of phytochemicals have been
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1. Defending against Cancer
a. Phytoestrogens mimic estrogen
1. Found in soybeans, legumes, flaxseeds, whole grains, fruits, and vegetables.
b. Lycopene
1. Powerful antioxidant.
watermelon.
c. Five servings of fruits and vegetables are recommended every day.
2. Defending against Heart Disease
a. Flavonoids in foods
1. Powerful antioxidants.
b. Carotenoids in foods, especially lutein and lycopene
1. Lower risk of heart disease.
2. Found in fruits and vegetables.
c. Phytosterols
1. May protect against heart disease.
2. Inhibit cholesterol absorption.
6. Lignans, found in flax seed and whole grains.
3. The Phytochemicals in Perspective
a. Difficult to assess one food and its benefits alone.
b. Actions of phytochemicals are complementary and overlapping.
B. Functional Foods PL V “‘Superfoods’ for Good Health,” “Good for You Foods”
1. Foods as Pharmacy
a. Margarine enhanced with a phytosterol may lower cholesterol.
2. Unanswered Questions
a. Research is lagging behind food manufacturers.
b. Consumer questions to ask
1. Does it work?
2. How much does it contain?
3. Is it safe?
4. Is it healthy?
C. Future Foods
1. Use of gene research.
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Case Study5
Belinda is a 10-year-old elementary school student who has come in for a physical examination. She is 4 feet 7
inches tall and weighs 120 pounds. Her doctor calculates her BMI at 27.9 (98th% for her age). Concerned about her
obesity, Belinda’s doctor asks about her diet and her physical activity. Her mother reports that Belinda has become
“lazy” and does not like to play outside with her friends after school. She says she is more irritable than usual and
complains about helping with household chores. Her mother worries that she may be depressed, although she can
think of no family issues that may be responsible for this behavior. Belinda sometimes skips breakfast or has cereal
and toast in the morning; she takes chips, a juice drink, and a cheese sandwich made with white bread for lunch; and
has a toaster pastry or cookies with milk for a snack after school. She doesn’t particularly like meat and frequently
asks for buttered pasta with cheese for dinner. Belinda says she eats vegetables “when my mom buys them.” A
blood test reveals a normal hemoglobin test with a low serum iron, a moderately elevated transferrin level, and a low
transferrin saturation.
1. Based on her history, what nutrient deficiencies would you suspect may contribute to Belinda’s symptoms?
Explain your answer.
2. What stage of iron deficiency do the results of her laboratory test indicate?
3. What are some meal planning changes that Belinda’s mother could make to improve Belinda’s intake of iron
and zinc?
4. What are some lunch and snack ideas that would improve Belinda’s intake of essential elements mentioned in
this chapter?
5. If her doctor prescribes an iron supplement, what practical advice would you give Belinda about when and how
to take it?
6. What cautions would you give Belinda’s mother regarding excessive supplementation of iron?
Answer Key:
1. Iron: common in growing children and adolescents; symptoms include fatigue, apathy, and irritability, and can
appear as behavior problems; often seen in overweight children; usual diet is low in good iron sources; lab
Suggested Classroom Activities
This chapter offers students the opportunity to learn many exciting things about the trace minerals. There is far too
much material for instructors to expect students to grasp in-depth information on all of them. Some instructors prefer
to encourage students to learn a great deal about iron. Because we do know so much about iron, it can be used to
illustrate many nutrition principles that may be more valuable than memorized details about individual nutrients.
