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ParT Two Nutrition: A Functional Approach 280 Contemporary 280 THEENERGY NUTRIENTS AND ENERGYBALANCE # 100121 Cust: war75543_overview_280_293.indd 280 McGraw Hill Au: Wardlaw www.mhhe.com/wardlawcontfa1 Pg. No. 280 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:56:57 AM overview of The MicronuTrienTs Overview of the Micronutrients 281 overview of The MicronuTrienTs Can food be medicine? Consider the following examples: • Fatigue, bleeding gums, bruising, and scaly skin . . . these are the symptoms of scurvy, which plagued seamen during long ocean voyages until 1753, when James Lind, a physician in the British Navy, identified that consumption of citrus fruits could prevent this disease. • Imagine the epidemic of rickets that occurred among children in post-Industrial Revolution Britain during the late eighteenth century. They suffered from bone pain; frequent fractures; weakness; and deformities, such as bowed legs. In 1922, cod liver oil was determined to be an effective treatment for rickets. • First noted in medical literature in the mid-sixteenth century, chlorosis was a disorder characterized by a green skin color, extreme weakness, and poor appetite. Chlorosis was mainly described among adolescent women, so some physicians of the era declared it to be a hysterical condition. In the early 1700s, the British physician Thomas Sydenham prescribed that afflicted women should drink “mineral water impregnated with the Iron Mine.” How do citrus fruits, cod liver oil, and mineral water prevent or cure such serious ailments? As nutrition science has evolved, the discovery of essential compounds in the foods we eat has overturned old misconceptions about the origins of some diseases. These essential compounds are collectively known as micronutrients. Citrus fruits, sure cures for scurvy, contain vitamin C. Cod liver oil, a preventive treatment for rickets, is an excellent source of vitamin D. The mineral water prescribed by Sydenham supplied iron for his patients suffering from chlorosis, a form of irondeficiency anemia. Vitamin C, vitamin D, and iron are a few examples of micronutrients. In Chapters 4, 5, and 6, you learned about carbohydrates, lipids, and proteins. Along with water, these energy-yielding nutrients are known as macronutrients. These are essential components needed in relatively large amounts (grams) in the human diet. On the other hand, micronutrients yield no energy and are required in small amounts (milligrams or micrograms). However slight its requirement, each micronutrient is necessary for one or more functions in the body (Overview Fig. 1). Too little or too much of any specific micronutrient leads to deterioration of physical health. The micronutrients can be chemically grouped based upon the presence of carbon atoms bonded to hydrogen atoms in their chemical structures. Organic micronutrients are classified as vitamins and inorganic micronutrients are classified as minerals. By definition, vitamins are essential organic (carbon-containing) substances needed in small amounts in the diet for normal function, growth, and maintenance of the body. In general, humans require a total of about 1 ounce (28 grams) of vitamins for every 150 pounds (70 kilograms) of food consumed. Vitamins can be divided into two broad classes based on solubility. Vitamins A, D, E, and K are # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 281 characterized by weakness, fatigue, slow wound healing, opening of previously healed wounds, bone pain, fractures, sore and bleeding gums, diarrhea, and pinpoint hemorrhages on the skin. rickets A disease characterized by poor mineralization of newly synthesized bones because of low calcium content. Arising in infants and children, this deficiency is caused by insufficient amounts of the vitamin D hormone in the body. chlorosis In traditional medical terminology, a form of iron-deficiency anemia characterized by pale or greenish skin, weakness, fatigue, and shortness of breath. In modern medical literature, chlorosis is termed hypochromic anemia. micronutrient A nutrient needed in milligram or microgram quantities in a diet. vitamin Compound needed in small viTaMins: viTal DieTarY coMPonenTs war75543_overview_280_293.indd 281 scurvy The vitamin C deficiency disease C/M/Y/K amounts in the diet to help regulate and support chemical reactions and processes in the body. mineral Element used in the body to promote chemical reactions and to form body structures. DESIGN SERVICES OF carlisle 1/23/08 9:57:01 AM 282 Contemporary Nutrition: A Functional Approach www.mhhe.com/wardlawcontfa1 overview figure 1 c Micronutrients contribute to many functions in the body. Bone Health Energy Metabolism Vitamin C Vitamin D Vitamin K Calcium Phosphorus Magnesium Fluoride Boron Silicon Thiamin Riboflavin Niacin Pantothenic acid Biotin Vitamin B-12 Iodide Chromium Manganese Molybdenum Fluid and Electrolyte Balance Antioxidant Systems Vitamin A Vitamin C Vitamin E Carotenoids Selenium Zinc Copper Manganese Sodium Potassium Chloride Phosphorus Blood Health Vitamin B-6 Vitamin B-12 Folate Vitamin K Iron Zinc Copper fat-soluble vitamin Vitamins that dissolve in fat and such substances as ether and benzene but not readily in water. These vitamins are A, D, E, and K. water-soluble vitamins Vitamins that dissolve in water. These vitamins are the B vitamins and vitamin C. # 100121 Cust: war75543_overview_280_293.indd 282 fat soluble (Overview Table 1), whereas the B vitamins and vitamin C are water soluble (Overview Table 2). The B vitamins include thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin B-6, folate, and vitamin B-12. Choline is a related nutrient, but is not classified as a vitamin. Vitamins are generally essential in human diets because they can’t be synthesized in the human body or because their synthesis can be decreased by environmental factors. Notable exceptions to having a strict dietary need for a vitamin are vitamin A, which we can synthesize from certain pigments in plants; vitamin D, synthesized in the body if the skin is exposed to adequate sunlight; niacin, synthesized from the amino acid tryptophan; and vitamin K and biotin, synthesized to some extent by bacteria in the intestinal tract. To be classified as a vitamin, a compound must meet the following criteria: (1) the body is unable to synthesize enough of the compound to maintain health; and (2) absence of the compound from the diet for a defined period produces deficiency symptoms that, if caught in time, are quickly cured when the substance is resupplied. A substance does not qualify as a vitamin merely because the body can’t make it. Evidence must suggest that health declines when the substance is not consumed. As scientists began to identify various vitamins, related deficiency diseases such as scurvy and rickets were dramatically cured. For the most part, as the vitamins were discovered, they were named alphabetically: A, B, C, D, E, and so on. Later, many substances originally classified as vitamins were found not to be essential for humans and were dropped from the list. Other vitamins, thought at first to be only one chemical turned out to be several chemicals, so the alphabetical names had to be broken down by numbers (B-6, B-12, and so on). McGraw Hill Au: Wardlaw Pg. No. 282 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:05 AM Overview of the Micronutrients 283 overview Table 1 Summary of the Fat-Soluble Vitamins Vitamin Major Functions RDA or Adequate Intake Dietary Sources Deficiency Symptoms Toxicity Symptoms Vitamin A • Promote vision: Females: 700 Preformed Vitamin A: • Night blindness • Fetal (preformed night and color micrograms RAE • Liver • Xerophthalmia malformations vitamin A and • Promote growth • Fortified milk • Poor growth • Hair loss provitamin A) • Prevent drying Males: 900 • Fortified • Dry skin • Skin changes of skin and eyes micrograms RAE breakfast • Bone pain • Promote cereals • Fractures resistance to 2300–3000 IU if bacterial infection as preformed Provitamin A: Upper Level is and overall immune (vitamin A) • Sweet potatoes 3000 micrograms system function • Spinach of preformed • Greens vitamin A • Carrots (10,000 IU) based • Cantaloupe on the risk birth • Apricots defects and liver • Broccoli toxicity Vitamin D • Increase 5–15 micrograms • Vitamin D • Rickets in • Growth absorption of fortified milk children retardation calcium and (200–600 IU) • Fortified • Osteomalacia • Kidney damage phosphorus breakfast in adults • Calcium • Maintain optimal cereals deposits in blood calcium • Fish oils soft tissue and calcification • Sardines of bone • Salmon Upper Level is 50 micrograms (2000 IU) based on the risk of elevated blood calcium Vitamin E • Antioxidant 15 milligrams • Plant oils • Hemolysis of • Muscle prevents alpha-tocopherol • Products made red blood cells weakness breakdown of from plant oils • Nerve • Headaches vitamin A and 22 IU natural • Some greens degeneration • Nausea unsaturated form, 33 IU • Some fruits • Inhibition of fatty acids (synthetic form) • Nuts and seeds vitamin K • Fortified metabolism breakfast cereals Upper Level is 1000 milligrams (1100 IU synthetic form, 1500 IU natural form) based on the risk of hemorrhage Vitamin K • Activation of Females: 90 • Green blood-clotting micrograms vegetables factors • Liver • Activation of Males: 120 • Some plant oils proteins micrograms • Some calcium involved in supplements bone metabolism • Hemorrhage • Fractures No Upper Level has been set Abbreviations: RAE = retinol activity equivalents; IU = international units war75543_overview_280_293.indd 283 # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 283 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:05 AM 284 Contemporary Nutrition: A Functional Approach www.mhhe.com/wardlawcontfa1 OVERVIEW Table 2 Summary of the Water-Soluble Vitamins and Choline Vitamin Major Functions RDA or Adequate Intake Dietary Sources* Thiamin • Coenzyme of 1.1–1.2 • Sunflower seeds carbohydrate milligrams • Pork metabolism • Whole and • Nerve function enriched grains • Dried beans • Peas Deficiency Symptoms Toxicity Symptoms Beriberi • Nervous tingling • Poor coordination • Edema • Heart changes • Weakness None Riboflavin† • Coenzyme of 1.1–1.3 carbohydrate milligrams metabolism • Milk • Inflammation of the • Mushrooms mouth and tongue • Spinach • Cracks at the corners • Liver of the mouth • Enriched grains • Eye disorders None Niacin • Coenzyme of 14–16 energy milligrams metabolism (niacin • Coenzyme of equivalents) fat synthesis • Coenzyme of fat breakdown • Mushrooms • Bran • Tuna • Salmon • Chicken • Beef • Liver • Peanuts • Enriched grains Upper Level is 35 milligrams from supplements, based on flushing of skin Pantothenic acid • Coenzyme of 5 milligrams energy metabolism • Coenzyme of fat synthesis • Coenzyme of fat breakdown • Mushrooms • No natural • Liver deficiency • Broccoli disease or • Eggs symptoms Biotin • Coenzyme of 30 micrograms glucose production • Coenzyme of fat synthesis • Cheese • Egg yolks • Cauliflower • Peanut butter • Liver Pellagra • Diarrhea • Dermatitis • Dementia • Death None Most foods have some • Coenzyme of 1.3–1.7 • Animal protein Vitamin B-6† protein milligrams foods metabolism • Spinach • Neurotransmitter • Broccoli synthesis • Bananas • Hemogloblin • Salmon synthesis • Sunflower seeds Many other functions • Dermatitis • Tongue soreness • Anemia • Depression Unknown • Headache • Anemia • Convulsions • Nausea • Vomiting • Flaky skin • Sore tongue Upper Level is 100 milligrams, based on nerve destruction • Green leafy • Megaloblastic None likely Folate (folic acid)† • Coenzyme involved 400 micrograms in DNA synthesis (dietary folate vegetables anemia equivalents) • Orange juice • Inflammation Upper Level for Many other functions • Organ meats of tongue adults set at • Sprouts • Diarrhea 1000 micrograms • Sunflower seeds • Poor growth for synthetic folic • Depressionacid (exclusive of food folate), based on masking of B-12 deficiency # 100121 Cust: war75543_overview_280_293.indd 284 McGraw Hill Au: Wardlaw Pg. No. 284 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:06 AM Overview of the Micronutrients 285 Vitamin Major Functions RDA or Adequate Intake Dietary Sources* Deficiency Symptoms Toxicity Symptoms Vitamin B-12† • Coenzyme of 2.4 micrograms • Animal foods • Macrocytic folate metabolism (not natural in plants) anemia • Nerve function Older adults and • Organ meats • Poor nerve vegans should use • Oysters function Many other functions fortified foods or • Clams supplements. • Fortified, ready-to-eat breakfast cereals None Vitamin C • Connective tissue 75–90 • Citrus fruits • Scurvy synthesis milligrams • Strawberries • Poor wound • Hormone synthesis • Broccoli healing • Neurotransmitter Smokers should • Greens • Pinpoint synthesis add 35 hemorrhages • Possible antioxidant milligrams • Bleeding gums activity Upper Level is 2 grams, based on development of diarrhea Choline† • Neurotransmitter 425–550 synthesis milligrams • Phospholipid synthesis Can also alter some diagnostic tests Widely distributed No natural Upper Level is 3.5 in foods and deficiency grams per day synthesized by based on devel- the bodyopment of fishy body odor and reduced blood pressure *Fortified ready-to-eat breakfast cereals are good sources for most of these vitamins and a common source of B vitamins for many of us. These nutrients also participate in homocysteine metabolism, which in turn may reduce the risk of developing cardiovascular disease. † In addition to their use in correcting deficiency diseases, a few vitamins have also proved useful in treating several nondeficiency diseases. These medical applications require administration of megadoses, well above typical human needs for the vitamins. For example, megadoses of a form of niacin can be used as part of blood cholesterol-lowering treatment for certain individuals. Still, any claimed benefits from use of vitamin supplements, especially intakes in excess of the Upper Level (if set), should be viewed critically because unproved claims are common. Plant and animal foods supply vitamins in the human diet. Vitamins isolated from foods or synthesized in the laboratory are the same chemical compounds and work equally well in the body. Contrary to claims in the health-food literature, “natural” vitamins isolated from foods are, for the most part, no more healthful than those synthesized in a laboratory, but there are exceptions. Vitamin E is much more potent in its natural form. In contrast, synthetic folic acid, the form of the vitamin added to ready-to-eat breakfast cereals and flour, is 1.7 times more potent than the natural vitamin form. megadose Intake of a nutrient beyond estimates of needs to prevent a deficiency or what would be found in a balanced diet; two to 10 times human needs is a starting point for such a dosage. Absorption and Storage of Vitamins in the Body The fat-soluble vitamins A, D, E, and K are absorbed along with dietary fat. These vitamins then travel with dietary fats as part of chylomicrons through the bloodstream to reach body cells. Special carriers in the bloodstream help distribute some of these vitamins. Fat-soluble vitamins are stored mostly in the liver and fatty tissues. When fat absorption is efficient, about 40% to 90% of the fat-soluble vitamin is absorbed. Anything that interferes with normal digestion and absorption of fats, however, also interferes with fat-soluble vitamin absorption. For example, people with cystic fibrosis, a disease that often hampers fat absorption, may develop deficiencies of fat-soluble vitamins. Some medications, such as the weight-loss drug orlistat (Xenical), discussed in Chapter 7, also interfere with fat absorption. Unabsorbed fat carries these vitamins to the war75543_overview_280_293.indd 285 # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 285 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:07 AM 286 Contemporary Nutrition: A Functional Approach www.mhhe.com/wardlawcontfa1 bioavailability The degree to which an ingested nutrient is absorbed and thus is available to the body. large intestine, where they are excreted in the feces. People with such conditions are especially susceptible to vitamin K deficiency because body stores of vitamin K are lower than those of the other fat-soluble vitamins. Vitamin supplements, taken under a physician’s guidance, are part of the treatment for preventing a vitamin deficiency associated with fat malabsorption. Finally, people who use mineral oil as a laxative at mealtimes risk fat-soluble vitamin deficiencies. The intestine does not absorb mineral oil, so fat-soluble vitamins are eliminated with the mineral oil in the feces. Water-soluble vitamins are handled much differently than fat-soluble vitamins. After being ingested, the B vitamins are first broken down from their active coenzyme forms into free vitamins in the stomach and small intestine. The vitamins are then absorbed, primarily in the small intestine. Typically, about 50% to 90% of the B vitamins in the diet are absorbed, which means they have relatively high bioavailability. Water-soluble vitamins are transported to the liver via the portal vein and are distributed to body tissues. Once inside cells, the active coenzyme forms are resynthesized. There is no need to consume the coenzyme forms. Some vitamins are sold in their coenzyme forms but these are broken down during digestion and we activate them when needed. Except for vitamin K, the fat-soluble vitamins are not readily excreted from the body. In contrast, excesses of the water-soluble vitamins are rapidly lost from the body, partly because the water in cells dissolves these vitamins and excretes them out of the body via the kidneys. Water-soluble vitamins B-6 and B-12 are exceptions; these are stored much more readily than the other water-soluble vitamins. The limited storage of many vitamins dictates that they should be consumed in the diet daily, although an occasional lapse in the intake of even water-soluble vitamins causes no harm. Symptoms of a vitamin deficiency occur only when that vitamin is lacking in the diet and the body stores are essentially exhausted. For example, an average person must consume no thiamin for 10 days or no vitamin C for 20 to 40 days before developing the first symptoms of deficiency of these vitamins. Vitamin Toxicity Intakes in excess of daily needs for the water-soluble vitamins are rapidly lost from the body because the kidneys efficiently filter the excess from the blood and excrete these compounds in urine. Notable exceptions are vitamin B-6 and vitamin B-12, stored in the liver. Although they are water-soluble, these two B vitamins may accumulate to toxic levels. In contrast to the water-soluble vitamins, fat-soluble vitamins are not readily excreted, so some can easily accumulate in the body and cause toxic effects. Although a toxic effect from an excessive intake of any vitamin is theoretically possible, toxicity of the fat-soluble vitamin A is the most frequently observed. With long-term intake, Vitamin A causes toxicity in as little as two times human need. Vitamin E and the water-soluble vitamins niacin, vitamin B-6, and vitamin C can also cause toxic effects, but only when consumed in large amounts (15 to 100 times human needs or more). vvitamins are unlikely to cause toxic effects unless taken in supplement (pill) form. Some people believe that consuming vitamins far in excess of their needs provides them with extra energy, protection from disease, and prolonged youth. They seem to think that if a little is good, then more must be better. A “one-a-day” type of multivitamin and mineral supplement usually contains less than two times the Daily Values of the components, so daily use of these products is unlikely to cause toxic effects in men and nonpregnant women. But consuming many vitamin pills, especially potent sources of vitamin A, can cause problems. Today, concentrated vitamin A supplements are widely available in grocery, drug, and health-food stores and pose risks for toxicity when used inappropriately. Preservation of Vitamins in Foods Good sources of vitamins can be found in all food groups, especially fruits and vegetables (Overview Figure 2). Substantial amounts of vitamins can be lost from the time a fruit or vegetable is picked until it is eaten. The water-soluble vitamins, particularly # 100121 Cust: war75543_overview_280_293.indd 286 McGraw Hill Au: Wardlaw Pg. No. 286 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:07 AM Overview of the Micronutrients 287 MyPyramid: Sources of Vitamins and Choline Grains • Thiamin • Riboflavin • Niacin • Folic acid Vegetables • Vitamin A • Vitamin K • Folate • Vitamin C Fruits • Vitamin A • Vitamin C Oils • Vitamin E Milk • Vitamin D • Riboflavin • Vitamin B-12 • Choline overview figure 2 c Certain groups of MyPyramid are especially rich sources of various vitamins and choline. This is true for those listed. Each may be also found in other groups in the pyramid but in lower amounts. Pantothenic acid is also present in moderate amounts in many groups. Meat & Beans • Thiamin • Riboflavin • Niacin • Biotin • Vitamin B-6 • Vitamin B-12 • Choline thiamin, vitamin C, and folate, can be destroyed with improper storage and excessive cooking. Heat, light, exposure to the air, cooking in water, and alkalinity are factors that can destroy vitamins. The sooner a food is eaten after harvest, the less chance of nutrient loss. Frozen vegetables and fruits are often as nutrient-rich as freshly picked ones because fruits and vegetables are often frozen immediately after harvesting. As part of the freezing process, vegetables are quickly blanched in boiling water. This destroys the enzymes that would otherwise degrade the vitamins. If a food is not eaten within a few days, freezing is the best preservation method to retain nutrients. Minerals: An Overview Whereas vitamins are compounds consisting of many elements (e.g., carbon, oxygen, and hydrogen), minerals are individual chemical elements. The mineral content of foods is sometimes called “ash” because it is all that remains after the whole food has been destroyed by high temperatures or chemical degradation. In humans, minerals make up about 4% of adult body weight (Overview Figure 3). A mineral is essential for humans if a dietary inadequacy results in a physiological or structural abnormality, and its addition to the diet prevents such illness or reinstates normal health. Sixteen minerals are known to be essential in the diet. Minerals are categorized based on the amount we need per day. Recall from Chapter 1 that if we require greater than 100 milligrams (1/50 of a teaspoon) of a mineral per day, it is considered a major mineral (Overview Table 3). These include calcium, phosphorus, magnesium, sulfur, sodium, potassium, and chloride. Trace minerals are required at levels less than 100 milligrams per day (Overview Table 4). Nine essential trace minerals (iron, zinc, copper, iodine, selenium, molybdenum, fluoride, manganese, and chromium) have been identified for humans. There are several additional trace minerals (sometimes called ultratrace minerals) found in the human war75543_overview_280_293.indd 287 # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 287 C/M/Y/K major mineral Vital to health, a mineral required in the diet in amounts greater than 100 milligrams per day. trace mineral Vital to health, a mineral required in the diet in amounts less than 100 milligrams per day. ultratrace mineral A mineral present in the human diet in trace amounts but that has not been shown to be essential to human health. DESIGN SERVICES OF carlisle 1/23/08 9:57:08 AM 288 Contemporary Nutrition: A Functional Approach www.mhhe.com/wardlawcontfa1 overview figure 3 c Approximate 1200 1200 1100 Some trace minerals Major minerals 1000 Grams in Human Body amounts of various minerals present in the average human body. Other trace minerals of nutritional importance not listed include chromium, fluoride, molybdenum, selenium, and zinc. 900 800 700 650 600 500 400 300 100 100 ide er pp Co ese an 0.03 Iod 0.12 0.16 ng esi gn 10 n um ide Ma Ch lor m diu So r lfu Su m siu tas Po ho osp Ph Ca lciu m rus 30 Iro 180 100 Ma 200 200 Minerals body, but many of them have no known requirements. These include arsenic, boron, nickel, silicon, and vanadium. Absorption and Storage of Minerals in the Body oxalic acid (oxalate) An organic acid found in spinach, rhubarb, and other leafy green vegetables that can depress the absorption of certain minerals present in the food, such as calcium. phytic acid (phytate) A constituent of plant fibers that binds positive ions to its multiple phosphate groups. # 100121 Cust: war75543_overview_280_293.indd 288 Foods offer us a plentiful supply of many minerals, but the ability of our bodies to absorb and use them varies. The bioavailability of minerals depends on many factors, including many nonmineral components of foods. Age, gender, genetic variables, nutritional status, and diet will affect mineral absorption and bioavailability. Numerous prescription drugs also adversely affect mineral absorption. The mineral content listed in a food composition table for the amount of a mineral in a food is a starting point for estimating the contribution the food will make to our mineral needs. Components of fiber, such as phytic acid (phytate) and oxalic acid (oxalate), can limit absorption of some minerals by binding to them. Spinach, for example, contains plenty of calcium, but only about 5% (compared to the typical 25% bioavailability of calcium from foods) of it can be absorbed because of the vegetable’s high concentration of oxalic acid, which binds calcium. High-fiber diets—particularly those in excess of current recommendations of 25 (adult women) to 38 (adult men) grams of fiber per day—can decrease the absorption of iron, zinc, and possibly other minerals. Many minerals, such as magnesium, calcium, iron, and copper, are of similar sizes and electrical charges. Having similar sizes and the same electrical charge causes these minerals to compete with each other for absorption, and therefore they affect each other’s bioavailabilty. An excess of one mineral decreases the absorption and metabolism of other minerals. For example, a large intake of zinc decreases copper absorption. Therefore, people should avoid taking individual mineral supplements unless a dietary deficiency or medical condition specifically warrants it. Food sources, however, pose little risk for these mineral interactions, giving us another reason to emphasize foods in meeting nutrient needs. McGraw Hill Au: Wardlaw Pg. No. 288 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:10 AM Overview of the Micronutrients 289 OVERVIEW Table 3 Summary of the Major Minerals Mineral Major Functions RDA, or Adequate Intake Dietary Sources Deficiency Symptoms Toxicity Symptoms Sodium • Major positive ion Age 19–50 years: • Table salt • Muscle cramps • Contributes to of the extracellular 1500 milligrams • Processed foods hypertension in fluid Age 51–70 years: • Condiments susceptible • Aids nerve impulse 1300 milligrams • Sauces individuals transmission Age > 70 years • Soups • Increases • Water balance 1200 milligrams • Chips calcium loss in urine • Upper Level is 2300 milligrams Potassium • Major positive ion 4700 milligrams of intracellular fluid • Aids nerve impulse transmission • Water balance • Spinach • Irregular heart beat • Slowing of the • Squash • Loss of appetite heartbeat, as • Bananas • Muscle cramps seen in kidney • Orange juice failure • Milk • Meat • Legumes • Whole grains Chloride • Major negative ion 2300 milligrams • Table salt • Convulsions in • Linked to of extracellular • Some infants hypertension in fluid vegetables susceptible • Participates in acid • Processed people when production in foods combined with stomach sodium • Aids nerve impulse • Upper Level is transmission 3600 milligrams • Water balance Calcium • Bone and tooth Age 9–18 years: • Dairy products • Increased risk • May cause kidney structure 1300 milligrams • Canned fish of osteoporosis stones and other • Blood clotting • Leafy problems in • Aids in nerve impulse Age > 18 years: vegetables susceptible people transmission 1000–1200 milligrams • Tofu • Upper Level is • Muscle contractions • Fortified orange 2500 milligrams • Other cell functions juice (and other fortified foods) • Dairy products • Possibility of • Impairs bone Phosphorus • Major ion of Age 9–18 years: intracellular fluid 1250 milligrams • Processed foods poor bone health in people • Bone and tooth • Fish maintenance with kidney failure strength • Soft drinks • Poor bone • Part of various Age > 18 years: • Bakery mineralization if metabolic 700 milligrams products calcium intakes compounds • Meats are low • Acid/base balance • Upper Level is 3 to 4 grams Magnesium • Bone formation Men: • Wheat bran • Weakness • Causes diarrhea and • Aids enzyme 400–420 milligrams • Green • Muscle pain weakness in people function vegetables • Poor heart with kidney failure • Aids nerve and Women: • Nuts function • Upper Level is heart function 310–320 milligrams • Chocolate 350 milligrams, but • Legumes refers to nonfood sources (e.g., supplements) only Sulfur • Part of vitamins and amino acids • Aids in drug detoxification • Acid/base balance war75543_overview_280_293.indd 289 None • Protein foods # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 289 • None observed C/M/Y/K • None likely DESIGN SERVICES OF carlisle 1/23/08 9:57:10 AM OVERVIEW Table 4 A Summary of Key Trace Minerals Mineral Major Functions RDA, or Adequate Intake Dietary Sources Deficiency Symptoms Toxicity Symptoms Iron • Components of Men: • Meats • Fatigue • Liver and heart hemoglobin and 8 milligrams • Seafood • Anemia damage other key compounds • Broccoli • Low blood (extreme used in respiration Premenopausal • Peas hemoglobin cases) • Immune function Women: • Bran values • GI upset • Cognitive 18 milligrams • Enriched • Upper Level is development breads 45 milligrams Zinc • Required for nearly Men: • Seafood • Skin rash • Reduced copper 200 enzymes 11 milligrams • Meats • Diarrhea absorption • Growth • Greens • Decreased • Diarrhea • Immunity Women: • Whole grains appetite and • Cramps • Alcohol metabolism 8 milligrams sense of taste • Depressed immune • Sexual development • Hair loss function • Reproduction • Poor growth and • Upper Level is • Antioxidant protection development 40 milligrams • Poor wound healing Selenium • Part of an 55 micrograms • Meats • Muscle pain • Nausea antioxidant system • Eggs • Weakness • Vomiting • Fish • Form of heart • Hair loss • Seafood disease • Weakness • Whole grains • Liver disease • Upper Level is 400 micrograms Iodide • Component of 150 micrograms • Iodized salt • Goiter • Inhibition of thyroid hormones • White bread • Mental thyroid gland • Saltwater fish retardation function • Dairy products • Poor growth in infancy • Upper Level is when mother is iodide 1.1 milligrams deficient during pregnancy Copper • Aids in iron 900 micrograms metabolism • Works with many antioxidant enzymes • Involved with enzymes of protein metabolism and hormone synthesis • Liver • Anemia • Vomiting • Cocoa • Low white • Nervous • Beans blood cell count system • Nuts • Poor growth disorders • Whole grains • Upper Level is • Dried fruits 8–10 milligrams Fluoride • Increases Men: • Fluoridated water • Increased risk • Stomach upset resistance of tooth 3.8 milligrams • Toothpaste of dental caries • Mottling (staining) of enamel to dental • Tea teeth during development caries Women: • Seaweed • Bone pain 3.1 milligrams • Dental treatments • Upper Level is 10 milligrams for adults Chromium • Enhances insulin 25–35 action micrograms • Egg yolks • High blood • Whole grains glucose after • Pork eating • Nuts • Mushrooms • Beer Caused by industrial contamination, not dietary excesses, so no Upper Level has been set Manganese • Cofactor of some 1.8–2.3 • Nuts None observed in • Nervous system enzymes, such as milligrams • Oats humans disorders those involved in • Beans • Upper Level is carbohydrate • Tea 11 milligrams metabolism • Works with some antioxidant systems Molybdenum • Aids in action of 45 micrograms some enzymes # 100121 Cust: war75543_overview_280_293.indd 290 McGraw Hill Au: Wardlaw Pg. No. 290 • Beans None observed in • Poor growth in • Grains healthy humans laboratory animals • Nuts • Upper Level is 2 milligrams C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:11 AM Overview of the Micronutrients 291 Several beneficial vitamin-mineral interactions occur during nutrient absorption and metabolism. When consumed in conjunction with vitamin C, absorption of certain forms of iron—such as that in plant products—improves. The active form of vitamin D hormone improves calcium absorption. Many vitamins require specific minerals to act as components in their structure and function. For example, the thiamin coenzyme requires magnesium or manganese to efficiently function. The average North American diet derives minerals from both plant and animal sources. Overall, minerals from animal products are better absorbed than those from plants because binders such as fiber are not present to hinder absorption. The mineral content of plants greatly depends on mineral concentrations of the soil in which they are grown. Vegans must be aware of the potentially poor mineral content of some plant foods and choose some concentrated sources of minerals. Soil conditions have less of an influence on the mineral content of animal products because livestock usually consume a variety of plant products grown from soils of differing mineral contents. Like vitamins, the majority of the minerals are absorbed in the small intestine. Minor amounts may be absorbed in the stomach, and some sodium and potassium is absorbed in the large intestine. After minerals are absorbed, some travel freely in the bloodstream, but many are carried by specific transport proteins to their site of action or storage. Calcium is one example of a mineral that can travel as an ion in the blood or bound to a blood protein called albumin. Iron, on the other hand, has damaging effects in its unbound form, so it is transported bound to proteins, such as transferrin. Minerals are stored in various tissues throughout the body. Some minerals must remain in the bloodstream to maintain fluid balance and supply body functions. Others, such as calcium, phosphorus, magnesium, and fluoride, are stored mainly in bones. Iron, copper, zinc, and many trace minerals are stored in the liver. Still others are stored in muscle tissue, organs, or glands. Mineral Toxicities An excessive mineral intake, especially of trace minerals such as iron and copper, can have toxic results. For many trace minerals, the gap between just enough and too much is small. Taking minerals as supplements poses the biggest threat for mineral toxicity, whereas food sources are unlikely culprits. Mineral supplements exceeding current standards for mineral needs—especially those that supply more than 100% of the Daily Values on supplement labels—should be taken only under a physician’s supervision. The Daily Values are for the most part higher than our current standards (e.g., Recommended Dietary Allowances [RDA]) for mineral needs. Without close monitoring, doses of minerals should not exceed any Upper Level set on a long-term basis. The potential for toxicity is not the only reason to carefully consider the use of mineral supplements. Harmful interactions with other nutrients are possible. Also, contamination of mineral supplements—with lead, for example—is a possibility. Use of brands approved by the United States Pharmacopeia (USP) lessens this risk. Even with the best intentions, people may harm themselves using mineral supplements. Preservation of Minerals in Foods Minerals are found in plant and animal foods (Overview Figure 4), but as you previously read, the bioavailability of minerals varies widely. Minerals are not typically lost from animal sources during processing, storage, or cooking, but for plant sources, significant amounts may be lost during food processing. When grains are refined, the final products have lost the majority of their vitamin E, many B vitamins, and trace minerals. The more refined a plant food, as in the case of white flour, the lower its mineral content. During the enrichment of refined grain products, iron is the only mineral added, whereas the selenium, zinc, copper, and other minerals lost during war75543_overview_280_293.indd 291 # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 291 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:12 AM 292 Contemporary Nutrition: A Functional Approach www.mhhe.com/wardlawcontfa1 MyPyramid: Sources of Minerals Grains • Sodium chloride • Calcium (fortified products) • Phosphorus • Magnesium • Iron • Zinc • Copper • Selenium • Chromium Vegetables • Potassium • Magnesium Fruits • Potassium • Boron Oils • None Milk • Calcium • Phosphorus • Zinc Meat & Beans • Sodium chloride (processed foods) • Potassium • Phosphorus • Magnesium • Selenium • Iron • Zinc • Copper overview figure 4 c Certain groups of MyPyramid are especially rich sources of various minerals. This is true for the minerals listed. Each mineral may also be found in other groups, but in lower amounts. Other trace minerals are also present in moderate amounts in many groups. With regard to the grains group, whole-grain varieties are the richest sources of most trace minerals listed. refinement are not replaced. Following the recommendation of the 2005 Dietary Guidelines for Americans to “make half your grains whole” will effectively preserve the mineral content of foods. The Functional Roles of Micronutrients The next four chapters will explore the vitamins and minerals from a functional perspective. The micronutrients will be grouped and discussed as they apply to various metabolic roles in the body. Keep in mind that each vitamin and mineral has multiple roles in metabolism. For example, calcium, best known for its role in bone formation, is also crucial for the transmission of nerve impulses through the body and plays a role in blood clotting. Vitamin C contributes to cellular antioxidant function, bone health, and metabolism of proteins. At all levels – cellular, tissue, organ, and whole body – vitamins and minerals clearly play important and interrelated roles in maintaining healthy body functions. Chapter 8 focuses on the roles of the micronutrients in fluid and electrolyte balance. Water balance requires sodium, potassium, chloride, and phosphorus. Levels of these minerals in the blood are tightly regulated by the body and imbalances can have dire consequences. In addition to maintaining the delicate balance between intracel- # 100121 Cust: war75543_overview_280_293.indd 292 McGraw Hill Au: Wardlaw Pg. No. 292 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:13 AM Overview of the Micronutrients 293 lular and extracellular water, these minerals participate in the transmission of nerve impulses and acid-base balance. Chapter 9 will enhance your understanding of the body’s antioxidant systems and how various vitamins and minerals take part in protecting tissues from oxidative damage. Vitamin E, vitamin C, vitamin A and its precursor carotenoids, as well as selenium are discussed in this chapter. In addition, the roles of beneficial plant chemicals in protection of human health will be explored. Before moving ahead in your study of vitamins and minerals as they participate in antioxidant systems (and energy metabolism, discussed in Chapter 11), it is important to understand how enzymes work. Enzymes are catalysts for biochemical reactions in living organisms. A catalyst is a compound that speeds the rate of a reaction but is not altered by the reaction. Most of the chemical reactions in the body would not occur, or would occur only at very slow rates, in the absence of catalysts. Enzymes allow for the breakdown of carbohydrates, lipids, and proteins to generate energy. They also catalyze synthetic reactions, such as the assembly of triglycerides for storage in adipose tissue. Enzymes are crucial players in antioxidant reactions, which neutralize damaging free radicals in the body. Beyond these few roles, thousands of other enzymes have been identified and studied. Typically, enzymes are made of proteins, but many such proteins require the aid of another compound (a cofactor, such as a coenzyme) for biological activity (Overview Figure 5). Frequently, the assisting compound is a vitamin or mineral, such as copper or selenium. In some reactions, numerous vitamins and minerals are required as coenzymes. Requirements for an enzyme and its coenzymes are specific, with little or no enzymatic activity observed if another coenzyme is substituted for the required one. Minerals are required for activation of about 30% of coenzyme all known enzymes. In Chapter 10, you will learn how micronutrients are vital to bone health. When we think of bone, we often imagine the hard, lifeless architecture of a skeleton hanging in the back of our high school science classroom. However, bone is a living and dynamic tissue that supports growth, houses nerves and blood vessels, produces blood cells, and helps regulate blood levels of certain minerals. This chapter explores the roles of calcium, phosphorus, vitamin D, vitamin K, magnesium, fluoride, and some other vitamins and ultratrace minerals in bone health. Chapter 11 delves into the roles of vitamins and minerals in energy metabolism and blood health. Although vitamins and minerals yield no energy to the body, they often participate as coenzymes in energy-yielding reactions. All of the B vitamins are involved in metabolism of the macronutrients, as are many trace minerals. Blood health encompasses immune function; clotting ability; and transport of oxygen, nutrients, and waste products. Blood health is influenced by vitamin K, iron, zinc, copper, and various B vitamins. Micronutrients are vital to every aspect of human health. Although requirements for vitamins and minerals are small, depriving the body of any one of these important dietary factors can be debilitating or deadly. For most healthy children and adults, foods are safe, effective, and enjoyable sources of vitamins and minerals, although dietary supplements may be useful under some circumstances. As you study the next four chapters, prepare to be amazed by the intricate interplay of micronutrients and human health. Inactive enzyme Vitamin coenzyme Active enzyme overview figure 5 c Coenzymes, such as those formed from B vitamins, aid in the function of various enzymes. Without the coenzyme, the enzyme cannot function, and deficiency symptoms associated with the missing vitamin eventually appear. Healthfood stores sell the coenzyme forms of some vitamins. These more expensive forms of vitamins are unnecessary. The body makes all the coenzymes it needs from vitamin precursors. enzyme A compound that speeds the rate of a chemical reaction but is not altered by the reaction. Almost all enzymes are proteins (some are made of genetic material). cofactor A substance that binds to a specific region on a protein, such as an enzyme, and is necessary for the protein’s function. coenzyme A compound (frequently a . vitamin or mineral) that combines with an inactive enzyme to form a catalytically active form. In this manner, coenzymes aid in enzyme function. war75543_overview_280_293.indd 293 # 100121 Cust: McGraw Hill Au: Wardlaw Pg. No. 293 C/M/Y/K DESIGN SERVICES OF carlisle 1/23/08 9:57:14 AM