1. Chapter 12 THE TRACE ELEMENTS

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Trace Elements Talk
The trace elements include iron, zinc, copper, manganese, selenium, iodine, fluoride, chromium and molybdenum.
They are required in amounts less than 100 mg per day.
Trace elements have been difficult to study, as they are difficult to remove from the diet.
Rate of bioavailability is a concern for trace elements.
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Iron in the Diet
Figure 12.1 Iron content of Canada’s Food Guide food groups
Both plant and animal foods are good sources of iron. The dashed lines represent the RDA for women of child-bearing age and for men and post-menopausal women.
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Iron Talk
Hemoglobin is the iron-containing component of the blood.
Iron from animal products is heme iron.
Iron from plant products is nonheme iron.
Iron cookware can be a source of nonheme iron in the diet.
Heme iron is more efficiently absorbed than nonheme iron.
Iron from the diet is absorbed into the intestinal mucosal cells.
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Heme Iron Absorption
1 Heme iron is absorbed as part of the heme group. Nonheme iron is absorbed in the ferrous form (Fe2+).
2 Once inside the mucosal cells, some iron may be bound to ferritin for storage.
3 When the mucosal cells die, iron that remains bound to ferritin is excreted in the feces.
4 Iron that enters the blood is converted to ferric iron (Fe3+) by a copper-containing protein in the cell membrane. The Fe3+ binds to transferrin for transport.
5 Transferrin transports iron to liver, bone, and other body cells.
6 When red blood cells die, they are broken down by cells in the liver, spleen, or bone marrow and the iron is released for reuse.
7 Excess iron is stored primarily in the liver, bound to ferritin.
8 Most iron loss is due to blood loss.
Figure 12.3 Iron absorption, transport, storage, and loss
The amount of iron that leaves the mucosal cells for transport to liver, bone, and other tissues is carefully regulated because little iron is lost from the body.
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Iron in the Body
Ferritin is the major iron storage protein.
Transferritin is an iron transport protein in the blood.
Hemosiderin is an insoluble iron storage compound produced by the body when iron exceeds the storage capacity of ferritin.
Iron is essential for the delivery of oxygen to cells. Two oxygen-containing proteins, hemoglobin and myoglobin, contain iron.
Most of the iron in the body is part of hemoglobin.
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DRIs for Iron
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DRIs for Iron
aThis value is an AI; all other values are RDAs. bValue is RDA X 1.8.
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Iron Deficiency
When iron is deficient, hemoglobin cannot be produced.
When there is insufficient hemoglobin, red blood cells are microcyctic and hypochromic and unable to deliver sufficient oxygen to the tissues. This is known as iron deficiency anemia.
It is estimated that as much as 80% of the world’s population may be iron deficient and 30% suffer from iron deficiency anemia.
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10. Iron and Zinc in the Canadian Diet
Source: Canadian Community Health Survey cycle 2.2, nutrition (2004). Available online at
nutrition/commun/index-eng.php. Accessed Sept 23, 2010.
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11. Iron Toxicity and Overload
Iron is essential for cellular metabolism, but too much can be toxic.
A UL has been set at 45 mg/day from all sources.
Iron poisoning can be life-threatening. It can damage the intestinal lining and cause abnormalities in body pH, shock and liver failure.
Iron overload can happen over time and accumulates in tissues such as the heart and the liver.
The most common form of iron overload is hemochromatosis.
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12. Zinc in the Canadian Diet
Figure 12.8 Zinc content of Canada’s Food Guide food groups
Meat, seafood, dairy products, and fortified foods are good sources of zinc; the dashed lines represent the RDA for adult men and women.
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13. Zinc in the Canadian Diet
CCHS suggests that a number of Canadians are not meeting their zinc requirements. The richest sources of zinc are found in animal products
Source: Health Canada. Canadian Nutrient File version Available online at Accessed August 21, 2011.
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Zinc in the Diet
Vegetarians are more vulnerable to having inadequate zinc intakes. Vegans my be 50% more vulnerable due to the lower bioavailability of zinc from vegan sources. Wise food choices are necessary.
Canadian regulations also require some foods, such as simulated meat products and beverages derived from legumes, nuts, cereal grains and potatoes, to be fortified with zinc. This information will be listed in the Nutrition Facts Table.
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Zinc Talk
Zinc is essential in the diet for growth and development.
Zinc from animal sources is better absorbed than zinc from plant sources.
Zinc can be bound by phytates, affecting bioavailability.
Zinc is the most abundant intracellular trace element.
Zinc is involved in the functioning of over 300 different enzymes, including superoxide dismutase, important for protecting cells from free radical damage.
Zinc can be toxic if taken in excess.
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Copper Talk
Copper may be important in helping to prevent certain types of anemia.
The richest dietary source of copper is organ meat. Seafood, chocolate, nuts, seeds and whole-grain foods are also good sources.
Zinc can decrease the bioavailability of copper.
The RDA for copper for adults is 900 micrograms per day.
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Manganese Talk
The best sources of manganese are whole grains and nuts.
Manganese is a constituent of some enzymes and an activator of other enzymes.
Manganese-requiring enzymes are involved in amino acid, carbohydrate and cholesterol metabolism, cartilage formation, urea synthesis and antioxidant protection.
Manganese, like copper and zinc, is needed for the activity of a form of superoxide dismutase.
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Selenium in the Diet
Figure Selenium content of Canada’s Food Guide food groups
Both plant and animal foods are good sources of selenium. The dashed line represents the RDA for adult men and women.
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Selenium Talk
The selenium content of plant foods, such as grains and seeds, depends on the selenium content of the soil in which they are grown.
Selenium deficiency can lead to Keshan disease, affecting the heart muscle.
Symptoms of selenium deficiency include muscular discomfort and weakness.
There may be a connection, still being researched, between diets low in selenium and higher incidences of cancer.
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Iodine Talk
The iodine content of food depends on the soil where plants are grown or where animals graze.
Soil near the ocean or sea is higher in iodine than soil inland.
Most of the iodine in the diet comes from iodized salt. Iodized salt is salt fortified with iodine. “Natural” sea salt may be very low in iodine.
More than half the iodine in the body is found in the thyroid gland.
Iodine is an essential component of thyroid hormones, including thyroxine.
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Thyroid Hormones
1 Thyroid hormones (T4 and T3) circulate in the blood bound to plasma proteins.
2 T4 and T3 enter the cell where a selenium-containing enzyme converts T4 to T3.
3 T3 enters the nucleus and binds to a nuclear protein receptor.
4 The T3-protein receptor complex then binds to a regulatory region of a target gene.
5 Transcription of the gene is turned on, increasing the amount of mRNA made.
6 mRNA directs translation, increasing the synthesis of the protein coded by this gene.
7 There is an increase in the amount of protein and hence the cellular functions and body processes affected by this protein.
Figure Role of thyroid hormones in gene expression
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22. Iodine and Thyroid Hormones
Figure Regulating thyroid hormone levels
When thyroid hormone levels drop too low, thyroid-stimulating hormone is released and stimulates the thyroid gland to take up iodine and synthesize more hormones. If iodine is not available (brown arrows), thyroid hormones cannot be made and the stimulation continues, causing the thyroid gland to enlarge.
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Iodine Talk
When the supply of iodine is adequate, the body can produce the needed thyroid hormones.
The RDA for iodine for adult men and women is 150 micrograms per day. The RDA for iodine is higher during pregnancy and lactation.
Consuming diets high in goitrogens, such as cabbage, cassava and millet, limits the bioavailability of iodine.
Iodine deficiency may result in hereditary cretinism.
The UL for adults is 1100 micrograms of iodine per day. Iodine toxicity is possible.
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Iodine Talk
All salt sold for household use in Canada, including sea salt, must be iodized (trace element iodine added).
Since the introduction of iodized salt in Canada, iodine intake has been adequate and iodine deficiency rare.
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Chromium Talk
Dietary sources of chromium include brewer’s yeast, liver, nuts and whole grains.
Cooking in stainless steel can increase food’s chromium content.
Chromium is involved in
carbohydrate
and lipid metabolism.
Figure Chromium and insulin function
a) When chromium is present, a small peptide inside cells becomes active and enhances the action of insulin by binding to the insulin receptor, which increases glucose uptake. b) When chromium is deficient, the active peptide is not formed and thus cannot bind the insulin receptor. The result is that insulin is less effective and less glucose can enter the cell.
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Fluoride Talk
Fluoride is important for dental health.
Fluoride is present in small amounts in almost all soil, water, plants and animals.
The most common sources of fluoride are fluoridated water, tea, marine fish eaten with their bones, such as canned salmon or sardines, and topical toothpaste.
Calcium-rich foods reduce the bioavailability of fluoride.
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27. Fluoride Talk (continued)
43% of the Canadian population receive fluoridated water, but there are substantial regional differences.
Fluoride intake has also increased due to the widespread use of fluoride toothpaste and fluoridated water in foods and beverages that are distributed in nonfluoridated areas.
Dental caries remain a public health problem. However, increased fluoride intake and advances in dental care have dramatically improved the dental health of the public.
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28. Fluoride Talk (continued)
Fluoridated water by region
Source: Health Canada. Fluoride in drinking water. Available online at Accessed May 4, 2011.
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29. Fluoride Talk (continued)
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Fluoride Toxicity
Figure 12.25
Too much dietary fluoride causes staining and pitting of the teeth. These photos compare normal teeth (left) and teeth showing enamel fluorosis (right). [cE.H. Gill/Custom Medical Stock Photo, Inc. (right) cNIH/Custom Medical Stock Photo, Inc.]
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31. Summary of Trace Elements
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32. Summary of Trace Elements (continued)
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33. Benefits and Risks of Trace Element Supplements
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34. Benefits and Risks of Trace Element Supplements
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