Nutrition chapter 12

Chromium

•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. (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.

Zinc fingers and gene expression

Finger-like structures called zinc fingers allow nuclear protein receptors that bind to vitamin A, vitamin D, and hormones to interact with the regulatory region of a gene and thus affect gene expression.

Molybdenum (Mo)

Function •Co-factor for enzymes involved in: -metabolism of sulfur-containing amino acids and nitrogen-containing compounds (DNA, RNA). -production of uric acid -oxidation/reduction of other compounds

Selenium spares vitamin E

Selenium is a part of the enzyme glutathione peroxidase, which neutralizes peroxides before they form free radicals. Fewer free radicals means less vitamin E is needed to eliminate them.

Selenium deficiency

The soil content of selenium affects the selenium content of crops grown in the soil. Because the diet in rural China consists predominantly of locally grown foods, the incidence of Keshan disease corresponds to the belt of selenium-deficient soil that crosses China from the northeast to the southwest.

Iodine and thyroid hormones

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.

Copper

•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.

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.

Fluoride

•Fluoride is important for dental health. •Present in small amounts in almost all soil, water, plants, and animals. •Most common sources of fluoride: fluoridated water, tea, marine fish eaten with their bones, and topical toothpaste. •Calcium-rich foods reduce the bioavailability of fluoride. •43% of the Canadian population receive fluoridated water, but there are substantial regional differences. •Fluoride intake has also increased due to 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.

Iron

•Hemoglobin: 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.

Iron toxicity and overload

•Iron is essential for cellular metabolism, but too much can be toxic. •UL = 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 liver. •Most common form of iron overload is hemochromatosis.

Other trace elements

•Lead, arsenic, boron, nickel, silicon, vanadium. •Found in minute amounts in the human body. •Arsenic: Organic form found in food is non-toxic. oDeficiency linked to nervous system disorders, blood vessel diseases, cancer •Boron: Involved in vitamin D and estrogen metabolism. •Nickel: Enzymes involved with amino and fatty acid metabolism. •Silicon: Synthesis of collagen and calcification of bone. •Vanadium: Insulin-like actions, stimulation of cell proliferation and differentiation. •Other trace elements: aluminum, bromine, cadmium, germanium, lead, lithium, rubidium, tin

Selenium

•Selenium content of plant foods (e.g., 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 between diets low in selenium and higher incidences of cancer (still being researched).

Iodine

•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 dietary iodine comes from iodized salt (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. •When iodine supply is adequate, the body can produce the needed thyroid hormones. •RDA for iodine for adult men and women = 150 mcg/day. •RDA is higher during pregnancy and lactation. •Consuming diets high in goitrogens (e.g., cabbage, cassava, millet) limits iodine bioavailability. •Iodine deficiency may result in hereditary cretinism. •Iodine toxicity is possible. •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.

Trace elements

•Trace elements include iron, zinc, copper, manganese, selenium, iodine, fluoride, chromium, and molybdenum. •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.

Zinc in the Canadian diet

•Vegetarians are more vulnerable to having inadequate zinc intakes. •Vegans may be 50% more vulnerable due to the lower bioavailability of zinc from vegan sources. •Wise food choices are necessary. •Canadian regulations require some foods (e.g., simulated meat products, beverages derived from legumes, nuts, cereal grains, and potatoes) to be zinc-fortified. This information will be listed in the Nutrition Facts Table.

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 (iron deficiency anemia). •Estimated 80% of the world's population may be iron deficient and 30% suffer from iron deficiency anemia. -Iron deficiency anemia is the final stage of iron deficiency. Inadequate iron first causes a decrease in the amount of stored iron, followed by low iron levels in the plasma. It is only after plasma levels drop that there is no longer enough iron available to maintain adequate hemoglobin in red blood cells.

Zinc

•Zinc is essential in the diet for growth and development. •Better absorbed from animal sources than plant sources. •Can be bound by phytates, affecting bioavailability. •Most abundant intracellular trace element. •Involved in the functioning of over 300 different enzymes, including superoxide dismutase, important for protecting cells from free radical damage. •Can be toxic if taken in excess.