Chapter 1 nutrition - Lecture notes 1 PDF

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Chapter 1 nutrition - Lecture notes 1 Fall of 2021...

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Chapter 7: LO 7.1 List the fat-soluble and water-soluble vitamins, and describe how solubility affects the absorption, transport, and excretion of each type. LO 7.2 Discuss the characteristics and functional aspects of fat-soluble vitamins. LO 7.3 Discuss the functional aspects, food sources, precursor, and effects of deficiency and toxicity of vitamin A. LO 7.4 Discuss the functional aspects, sources, and effects of deficiency and toxicity of vitamin D. LO 7.5 Discuss the functional aspects, food sources, and effects of deficiency and toxicity of vitamin E. LO 7.6 Discuss the functional aspects, food sources, and effects of deficiency and toxicity of vitamin K. LO 7.7 Summarize the characteristics and functional aspects of water-soluble vitamins. LO 7.8 Discuss the functional aspects, food sources, and effects of deficiency and toxicity of vitamin C. LO 7.9 Discuss the collective functional aspects of B vitamins in metabolism and the effects of their deficiencies. LO 7.10 Discuss the functional aspects, food sources, and effects of deficiencies and toxicities of each of the eight B vitamins. LO 7.11 Describe how to choose foods to meet vitamin needs. LO 7.12 List some valid reasons why vitamin supplements may be required by some people and should not be taken by others. vitaminsorganic compounds that are vital to life and indispensable to body functions but are needed only in minute amounts; noncaloric essential nutrients. Today, research hints that two of the major scourges of humankind, cardiovascular disease (CVD) and cancer, may be linked with low intakes of vitamins. the only disease a vitamin will cure is the one caused by a deficiency of that vitamin. As for chronic disease prevention, the evidence is still emerging. 7-1Definition and Classification of Vitamins 7-1 a vitamin is defined as an essential, noncaloric, organic nutrient needed in tiny amounts in the diet. The role of many vitamins is to help make possible the processes by which other nutrients are digested, absorbed, and metabolized or built into body structures. Although small in size and quantity, the vitamins accomplish mighty tasks. Table 7–1 Vitamin Names Fat-Soluble Vitamins Vitamin A Vitamin D Vitamin E Vitamin K Water-Soluble Vitamins

Fat-Soluble Vitamins Vitamin A B vitamins Thiamin (B1) Riboflavin (B2) Niacin (B3) Folate Vitamin B12 Vitamin B6 Biotin Pantothenic acid Vitamin C Certain vitamins occur in foods in a form known as precursors, or provitamins. Once inside the body, these are transformed chemically to one or more active vitamin forms. Thus, to measure the amount of a vitamin found in food, we often must count not only the amount of the true vitamin but also the vitamin activity potentially available from its precursors precursors, or provitaminscompounds that can be converted into active vitamins. The vitamins fall naturally into two classes: fat soluble and water soluble (listed in Table 7–1). Solubility confers on vitamins many of their characteristics. It determines how they are absorbed into and transported around by the bloodstream, whether they can be stored in the body, and how easily they are lost from the body. In general, like other lipids, fat-soluble vitamins are absorbed into the lymph, and they travel in the blood in association with protein carriers. Fat-soluble vitamins can be stored in the liver or with other lipids in fatty tissues, and some can build up to toxic concentrations. The water-soluble vitamins are absorbed directly into the bloodstream, where they travel freely. Most are not stored in tissues to any great extent; rather, excesses are excreted in the urine. Thus, the risks of immediate toxicities are not as great as for fat-soluble vitamins. This chapter examines the fat-soluble vitamins first and then the water-soluble ones. The tables at the end of the chapter sum up the basic facts about all of them. Furthermore, Health Canada recently announced the approval of new “nutrient function claims” for biotin and vitamin K, along with additional claims for vitamin A, vitamin C, Vitamin , and folate Ke Key y Po i n t

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Vitamins are essential, noncaloric nutrients that are needed in tiny amounts in the diet and help drive cell processes in the body. The fat-soluble vitamins are vitamins A, D, E, and K; the water-soluble vitamins are vitamin C and the B vitamins. 7-2The 7-2 The F Fatatat-Soluble Soluble Vitamins LO 7. 2 Discuss the characteristics and functional aspects of fat-soluble vitamins. The fat-soluble vitamins—A, D, E, and K—are found in the fats and oils of foods and require bile for absorption. Once absorbed, these vitamins are stored in the liver and fatty tissues until the body needs them. The body can survive weeks of consuming foods that lack these vitamins as long as the diet as a whole provides average amounts that approximate the recommended intakes. This capacity to be stored also sets the stage for toxic buildup if you take in too much. Excesses of vitamins A and D from supplements can reach toxic levels especially easily. Deficiencies of the fat-soluble vitamins are likely when the diet is consistently low in them. We also know that any disease that produces fat malabsorption (such as liver disease that prevents bile production) can cause the loss of vitamins dissolved in undigested fat and so bring about deficiencies. In the same way, a person who uses mineral oil (which the body can’t absorb) as a laxative risks losing fat-soluble vitamins because they dissolve in the oil and are excreted. Deficiencies are also likely when people eat diets that are extraordinarily low in fat because such diets interfere with absorption of these vitamins. Fat-soluble vitamins play diverse roles in the body. Vitamins A and D may act somewhat like hormones, directing cells to convert one substance to another, to store this, or to release that. Many of their effects are exerted at the level of the genes, influencing protein production. Vitamin E flows throughout the body, preventing oxidative destruction of tissues. Vitamin K is necessary for blood to clot. Each is worth a book in itself.

7-2aVitamin 7-2a Vitamin A LO 7. 3 Discuss the functional aspects, food sources, precursor, and effects of deficiency and toxicity of vitamin A. Vitamin A has the distinction of being the first fat-soluble vitamin to be recognized. Today, after a century of research, preformed vitamin A (e.g., retinol) and its plant-derived precursor, beta-carotene, are still very much a focus of research. Three forms of vitamin A are active in the body; one of the active forms, retinol, is stored in the liver. The liver makes retinol available to

the bloodstream and thereby to the body’s cells. The cells convert retinol to its other two active forms, retinal and retinoic acid, as needed. A Jack of All T Trad rad rades—V es—V es—Vitamin itamin A Vitamin A is a versatile vitamin, with roles in gene expression, vision, maintenance of body linings and skin, immune defences, growth of bones and of the body, and normal development of cells, and it is of critical importance for reproduction. In short, vitamin A is needed everywhere DRI R Recommended ecommended Intak Intakes: es: Men: 900 µg/d Women: 700 µg/d CCHS 2.2 Mean Intak Intake: e: Men: 590 RAE/d Women: 703 RAE/d Tolera olerable ble Upper Intake Lev Level: el: Adults: 3,000 µg vitamin A/d Chief Functions: Vision; maintenance of cornea, epithelial cells, mucous membranes, skin; bone and tooth growth; regulation of gene expression; reproduction; immunity Deficiency: Night blindness, corneal drying (xerosis), and blindness (xerophthalmia); impaired bone growth and easily decayed teeth; keratin lumps on the skin; impaired immunity Toxicity: Vitamin A: Increased activity of bone-dismantling cells causing reduced bone density and pain; liver abnormalities; birth defects Beta-carotene: Harmless yellowing of skin

Regulation of Gene Expression Vitamin A exerts considerable influence on body functions through its regulation of the activities of the genes. Genes direct the synthesis of proteins, including enzymes, and enzymes perform the metabolic work of the tissues (see Chapter 6). Hence, factors that influence gene expression also affect the metabolic activities of the tissues and the health of the body. Hundreds of genes have been suggested as regulatory targets of the retinoic acid form of vitamin A. Researchers have long known that simply possessing the genetic equipment needed to make a particular protein does not guarantee that the protein will be produced, any more than owning a car guarantees you a trip across town. To get the car rolling, you must also use the right key to trigger the events that start up its engine or turn it off at the appropriate time. Some dietary components, including the retinoic acid form of vitamin A, are now known to be such keys—they help activate or deactivate certain genes and thus affect the production of specific proteins. Eyesight The most familiar function of vitamin A, however, is in eyesight. Vitamin A plays two indispensable roles: in the process of light perception at the retina and in the maintenance of a healthy, crystal-clear outer window, the cornea (see the margin drawing). When light falls on the eye, it passes through the clear cornea and strikes the cells of the retina, bleaching many molecules of the pigment rhodopsin contained within those cells. Vitamin A is a part of the rhodopsin molecule. When bleaching occurs, the vitamin is broken off, initiating the signal that conveys the sensation of sight to the optic centre in the brain. The vitamin then reunites with the pigment, but a little vitamin A is destroyed each time this reaction takes place, and fresh vitamin A must regenerate the supply. If the supply begins to run low, a lag occurs before the eye can see again after a flash of bright light at night (see Figure 7–1). This lag in the recovery of night vision, termed night blindness, may indicate a vitamin A deficiency. A bright flash of light can temporarily blind even normal, well-nourished eyes, but if you experience a long recovery period before vision returns, your healthcare provider may want to check your vitamin A intake. A more profound deficiency of vitamin A is exhibited when the protein keratin accumulates and clouds the eye’s outer vitamin A–dependent part, the cornea. The condition is known as keratinization, and if the deficiency of vitamin A is not corrected, it can worsen to xerosis (drying) and then progress to thickening and permanent blindness, xerophthalmia. Tragically, a half million of the world’s vitamin A-deprived children become blind each year from this often preventable condition. If the deficiency is discovered early, capsules providing 60,000 micrograms of vitamin A taken twice each year can reverse it. Better still, a child fed fruits and vegetables regularly is virtually ensured of protection.

Skin and Body Linings Vitamin A is needed by all epithelial tissue (external skin and internal linings), not just by the cornea. The skin and all the protective linings of the lungs, intestines, vagina, urinary tract, and bladder serve as barriers to infection or damage from other sources. An example of vitamin A’s work behind the scenes at the genetic level is the process of cell differentiation, in which each type of cell develops to perform a specific function. When goblet cells (cells found in linings of the small intestine) mature, for example, they specialize in synthesizing and releasing mucus to protect delicate tissues from toxic particles or bacteria and other microbial invaders. If vitamin A is deficient, the cell differentiation and maturing process is impaired. Goblet cells, among others, fail to mature, then fail to make protective mucus, and eventually die off. Some of the cells in these areas are displaced by cells that secrete keratin, the protein mentioned earlier. Keratin is the same protein that provides toughness in hair and fingernails, but in the wrong place, like the skin, keratin makes the tissue surfaces dry, hard, and cracked. As dead cells accumulate on the surface, the tissue becomes vulnerable to infection (see Figure 7–2). In the cornea, keratinization leads to xerophthalmia; in the lungs, the displacement of mucusproducing cells makes respiratory infections likely; in the vagina, the same process leads to vaginal infections. The process of cell differentiation also has links to cancer. Cancer researchers are investigating the roles of retinoic acid in regulating genes that control cell differentiation because such genes may suppress or even reverse malignant cell changes leading to cancer. Immunity Vitamin A has gained a reputation as an “anti-infective” vitamin because so many of the body’s defences against infection depend on an adequate supply. Much research supports the need for vitamin A in the regulation of the genes that produce proteins involved in immunity. Without sufficient vitamin A, these genetic interactions produce an altered response to infection that weakens the body’s defences against disease. Using new technologies, researchers are close to developing a vitamin A-rich rice to serve as a staple food for the world’s children who lack vitamin A. See the Controversy section of Chapter 12 for details. When the defences are weak, especially in vitamin A-deficient children, an illness such as measles can become severe. A downward spiral of malnutrition and infection can set in. The child’s body must devote its scanty store of vitamin A to the immune system’s fight against the measles virus, but the infection causes vitamin A to be lost from the body. As vitamin A dwindles, the infection worsens. Even if the child survives the measles infection, blindness is likely. The corneas, already damaged by the chronic vitamin A shortage, degenerate rapidly as the child’s meager supply of vitamin A is diverted to the immune system.

Growth Vitamin A also assists in the growth of bone (and teeth). Normal children’s bones grow longer, and the children grow taller, by remodelling each old bone into a new, bigger version. To do so, the body dismantles the old bone structures and replaces them with new, larger bone parts. Growth cannot take place just by adding on to the original small bone; vitamin A is needed in the critical dismantling steps. In children, failure to grow is one of the first signs of poor vitamin A status. Restoring vitamin A to such children is imperative, but correcting dietary deficiencies may be more effective than giving vitamin A supplements alone because other nutrients from nutritious food are also needed for children to gain weight and grow taller. World hunger is a topic of Chapter 15. Vitamin A Deficien Deficiency cy around the W World orld Vitamin A deficiency presents a vast problem worldwide, placing a heavy burden on society. Between 3 million and 10 million of the world’s children suffer from signs of severe vitamin A deficiency—not only xerophthalmia and blindness but also diarrhea and reduced food intake that rapidly worsen their condition. A staggering 275 million more children suffer from milder deficiency that impairs immunity and promotes infections. In some areas of the world, vitamin A and other deficiencies seem to be the rule rather than the exception among new mothers and infants. In countries where children receive vitamin A supplements, childhood death rates have declined by half. Even in the United States, vitamin A supplements are recommended for certain groups of infants and for children with measles. Vitamin A supplementation also offers some protection against the complications of other lifethreatening infections, including malaria, lung diseases, and HIV. The World Health Organization (WHO) and United Nations International Children’s Emergency Fund (UNICEF) are working to eliminate vitamin A deficiency; achieving this goal would improve child survival throughout the developing world. Vitamin A T Toxicity oxicity Figure 7–3 shows that toxicity in people who take excess vitamin A in supplements or fortified foods compromises the tissues just as deficiency does and is equally dangerous. The many symptoms of vitamin A toxicity include abdominal pain, hair loss, joint pain, stunted growth, bone and muscle soreness, cessation of menstruation, nausea, diarrhea, rashes, damage to the liver, and enlargement of the spleen. The earliest symptoms of overdoses are loss of appetite, blurred vision, growth failure in children, headache, itching of the skin, and irritability. Over the years, even relatively small excesses may weaken the bones and contribute to hip fractures. Some foods contain substantial amounts of vitamin A (see Table 7–2). Some experts suggest that vitamin A supplements be reserved for treatment of true deficiencies caused by malabsorption or malnutrition.

Vitamin A from fortified foods and other rich sources can add up. The Tolerable Upper Intake Level (UL) for vitamin A is 3,000 µg/d. High-potency vitamin pill- 3,000 µg Calf’s liver, 30 g cooked- 2,300 µg Regular multivitamin pill- 1,500 µg Chicken liver, 30 g cooked- 1,400 µg “Complete” liquid supplement drink, 1 serving- 350–1,500 µg Cod-liver oil (1 tsp)- 1,350 µg Milk, 1 c- 150 µg Margarine, 1 tsp- 55 µg Pregnant women, especially, should be wary—chronic use of vitamin A supplements providing three to four times the amount recommended for pregnancy and prescription levels of a popular acne medication have caused malformations of the fetus. Even a single massive vitamin A dose (100 times the need) may do so. Children, who often mistake chewable vitamin pills for candy, are also likely to be hurt by vitamin A excesses because they need less and are more sensitive to overdoses. Adolescents may take massive vitamin A doses in the mistaken belief that vitamin A can correct acne. An effective acne medicine, Accutane, is derived from vitamin A, but it is chemically altered and given in carefully controlled dosages—vitamin A itself has no effect on acne. The effects of excessive vitamin A intakes during pregnancy are discussed in Chapter 13. Healthy people can eat foods naturally rich in vitamin A in large amounts without risking toxicity, with the possible exception of liver. When laboratory pigs eat chow made from salmon parts, including the livers, the animals stop growing and fall ill from vitamin A toxicity. Inuit people and Arctic explorers know that polar bear livers are a dangerous food source because the bears eat fish whole with the livers and concentrate large amounts of vitamin A. One ounce of ordinary liver offers three times the Dietary Reference Intakes (DRI) committee recommended intake of preformed vitamin A along with abundant nutrients of many kinds, and eating it occasionally can boost nutrient status. Daily use invites vitamin A toxicity, however, especially in young children and pregnant women who eat other fortified foods or take supplements. The Canadian and U.S. standard for vitamin A intake is the DRI recommended intake, listed on the DRI table. 

1 IU = 0.3 µg retinol Vitamin A R Recommendat ecommendat ecommendations ions The ability of vitamin A to be stored in the tissues means that although the vitamin A intake recommendation is given as a daily amount, you need not consume the vitamin every day. An average intake that meets the daily need over several months is sufficient. The amount of vitamin A you need

is proportional to your body weight. According to the DRI committee, a man needs a daily average of about 900 micrograms; a woman needs about 700 micrograms. During lactation, her need is higher. Children need less. A regular balanced diet that includes the recommended servings of vegetables and fruit each day supplies more than adequate amounts. Vitamin A recommendations are expressed in micrograms, but most food tables and supplement labels still express vitamin A contents using a different unit, the IU (international unit). Be careful to notice whether food tables or supplement labels use micrograms or IU. See the Aids to Calculations (Appendix B) for help in converting many kinds of units. When comparing vitamin A in foods, make sure that the amounts are all expressed in the same units. As for vitamin A supplements, the DRI committee and other nutrition agencies recom...