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Water-Soluble Vitamins Chapter 8
Terms in this set (90)
What are vitamins?
-Vitamins are organic compounds that are essential in the diet in small amounts to promote and regulate the processes necessary for growth, reproduction, and the maintenance of health.
-When a vitamin is lacking in the diet, deficiency symptoms occur. When the vitamin is restored to the diet, the symptoms resolve. Vitamins have traditionally been grouped based on their solubility in water or fat. This chemical characteristic allows generalizations to be made about how they are absorbed, transported, excreted, and stored in the body
-WATER-SOLUBLE VITAMINS=Vitamins B and C
-FAT-SOLUBLE VITAMINS= Vitamins A, D, E, and K
B Vitamins (water-soluble)
Vitamin B6 and Vitamin B12 are referred to by their numbers
Vitamins in Our Diet
Despite the variety of options for obtaining vitamins, it is still possible to consume too little of some vitamins, and the popularity of supplements has increased the likelihood that certain vita-mins will be consumed in excess.
Natural Food Sources of Vitamins
- Almost all foods contain some vitamins.
- Cooking and storage methods can cause vitamin loses.
Fortified Foods and Enriched Foods
- Fortification is the general term used to describe the process of adding nutrients to food, extending beyond government-mandated programs. (i.e. vitamin D being added to milk or orange juice with vitamin C)
- Enriched refers to a food that has had nutrients added to restore those lost in processing to a level equal to or higher than originally present.
-Refers to a food that has had nutrients added to restore those lost in processing to a level equal to or higher than originally present.
Dietary Supplements (could be an essay question) vs. Food
-While dietary supplements provide specific nutrients and can help some people meet their nutrient needs, they do not provide all of the benefits of a diet containing a wide variety of foods.
-Could be an essay question to come up with the reasons why food is better than supplements
Absorption, Storage, and Excretion of Vitamins
About 40 to 90% of the vitamins in food are absorbed primarily in the small intestine.
-A general term describing how well a nutrient can be absorbed and utilized by the body.
-The bioavailability of a vitamin depends on how much can be absorbed and used by the body and is influenced by a number of factors, such as the amount of fat in the diet, transport proteins, and form of vitamin (active provitamin or inactive precursor).
Storage and Excretion
-With the exception of vitamin B12, the water-soluble vitamins are easily excreted from the body in the urine whereas the fat-soluble vitamins are stored in the liver and fatty tissues and cannot be excreted in the urine.
What Vitamins Do
-Vitamins promote and regulate body activities, and each vitamin has one or more important functions
-Vitamins are needed to promote and regulate body processes that are essential for growth, reproduction, and tissue maintenance.
- Each vitamin has one or more functions: many are coenzymes and some are antioxidants
- More than one vitamin is typically needed to ensure the health of a particular organ or system.
-Vitamins do not provide energy. However many of the B vitamins are coenzymes essential for the proper functioning of enzymes involved in the metabolism of the energy-yielding nutrients. Without these coenzymes, the reactions that produce ATP cannot proceed
Meeting Vitamin Needs
Vitamin deficiencies remain a major health problem worldwide, but severe deficiencies are rare in developed countries.
Recommended Vitamin Intakes
- Recommended intakes for vitamins are expressed as RDAs or AIs with ULs expressing the high-est dose that is unlikely to cause toxicity.
-The label doesn't tell everything about the vitamin content of foods because vitamins can be lost by exposure to light or oxygen, washed away during preparation, or destroyed by cooking (Figure 8.8). Vitamin losses can be minimized through food preparation methods that reduce exposure to heat and light
-Frozen foods are frozen to minimize nutrient losses and thus may supply more vitamins than fresh foods
Vitamins on Food Labels
Food labels can help identify packaged foods that are good sources of vitamins.
-Thiamin was the first of the B vitamins to be identified and is therefore sometimes called vitamin B1.
- Beriberi, the disease that results from a thiamin deficiency
Thiamin in the Diet
-The best food sources of thiamin are lean pork, legumes, and whole or enriched grains.
- Thiamin in foods may be destroyed during cooking or storage as it is sensitive to heat, oxygen, and low-aid conditions.
How Thiamin Functions in the Body
-Thiamin is a vitamin, so it does not provide energy, but it is important in energy metabolism
- Thiamin, in its coenzyme form thiamin pyrophosphate, is required for the formation of acetyl-CoA from pyruvate and for a reaction in the citric acid cycle. Therefore, it is particularly important for the production of ATP from glucose.
- Thiamin deficiency, or beriberi, causes nervous system abnormalities and is common in alcohol-ics.
- Thiamin deficient alcoholics may develop a neurological condition known as Wernicke-Korsakoff syndrome which is characterized by mental confusion, psychosis, memory disturbances, and coma.
Recommended Thiamin Intake
The RDA is based on the amount of thiamin needed to achieve and maintain normal activity of a thiamin-dependent enzyme found in red blood cells and normal urinary thiamin excretion.
Thiamin Toxicity and Supplements
- No toxicity has been identified, so a UL for thiamin has not been established.
- Thiamin supplements containing up to 50 mg/day are widely available and are marketed with the promise that they will provide "more energy."
While searching for a cure for beriberi (i.e. Thiamin deficiency), scientists isolated riboflavin and several other B vitamins.
Riboflavin in the Diet
-Milk, meat, and enriched grain products are the best food sources of riboflavin.
- Riboflavin is destroyed by exposure to light, which is why milk doesn't come in glass bottles anymore
How Riboflavin Functions in the Body
- One of riboflavin's coenzymes, flavin adenine dinucleotide (FAD) functions in the citric acid cycle and is important for the breakdown of fatty acids.
- Flavin mononucleotide (FMN) and FAD both function as electron carriers in the electron transport chain.
-Therefore, adequate ribflavin is crucial in providing energy from carbohydrate, fat, and protein
-When riboflavin is deficient, injuries heal poorly because new cells cannot grow to replace the damaged ones.
- Ariboflavinosis is a condition resulting from a deficiency of riboflavin.
- Symptoms of ariboflavinosis include the inflammation of the eyes, lips, mouth, and tongue.
Recommended Riboflavin Intake
The RDA is based on the amount of riboflavin needed to achieve and maintain normal activity of a riboflavin-dependent enzyme found in red blood cells and normal urinary riboflavin excretion.
Riboflavin Toxicity and Supplements
- No adverse effects have been reported from overconsumption of riboflavin from foods or sup-plements.
- No toxicity has been identified.
-A niacin deficiency primarily affects the poor who cannot afford a varied diet.
-A deficiency of the B vitamin niacin results in a disease called pellagra, which causes progressive physical and mental deterioration
-The early symptoms of pellagra include fatigue, decreased appetite, and indigestion, followed by the three Ds: dermatitis, diarrhea, and dementia. If left untreated, niacin deficiency results in a fourth D—death
Niacin in the Diet
- Beef, chicken, turkey, fish, and enriched grain products are the best food sources of niacin.
- The amino acid tryptophan from dietary protein can meet some of the niacin requirements.
How Niacin Functions in the Body
-Niacin is important in the production of ATP from the energy-yielding nutrients as well as in reactions that synthesize other molecules
- The niacin coenzyme nicotinamide adenine dinucleotide (NAD) functions in glycolysis and the citric acid cycle, accepting released electrons and passing them on to the electron transport chain.
- The niacin coenzyme nicotinamide adenine dinucleotide phosphate (NADP) acts as an electron carrier in reactions that synthesize fatty acids and cholesterol.
- Niacin deficiency results in pellagra, which is characterized by dermatitis, diarrhea, dementia, and finally, if untreated, death.
Recommended Niacin Intake
- The RDA for niacin is expressed as niacin equivalents to take into account the tryptophan that is converted to niacin.
Niacin Toxicity and Supplements
- Supplements of the nicotinic acid form of niacin can lower elevated blood cholesterol but fre-quently cause toxicity symptoms such as flushing, tingling sensations, nausea, and a red skin rash.
Biotin was discovered when rats fed protein from raw egg white developed a syndrome of hair loss, dermatitis, and neuromuscular dysfunction.
Biotin in the Diet
- Liver and egg yolks are good sources of biotin.
- Avidin, a protein in raw egg white, tightly binds biotin and prevents its absorption.
How Biotin Functions in the Body
- Biotin in its coenzyme form is needed for the synthesis of glucose and fatty acids and for the metabolism of certain amino acids.
-It functions in energy metabolism because it is needed to make a four-carbon molecule necessary in the citric acid cycle and in gluconeogenesis. This B vitamin is also important in the synthesis of fatty acids and some amino acids
- Although biotin deficiency is uncommon, those experiencing protein-energy malnutrition or mal-absorptive disorders are at higher risk.
Recommended Biotin Intake
- An RDA has not been established for biotin because some of our requirement for this vitamin is met by bacterial synthesis in the GI tract.
- No toxicity has been reported.
- Pantothenic acid gets its name from the Greek word pantothen, meaning from everywhere, is a B vitamin that is widely distributed in foods
Pantothenic Acid in the Diet
- Pantothenic acid is particularly abundant in meat, eggs, whole grains, and legumes.
How Pantothenic Acid Functions in the Body
- Pantothenic acid is part of coenzyme A (CoA), which is required for the production of ATP from carbohydrate, fat, and protein, and the synthesis of cholesterol and fatty acids.
-It is part of coenzyme A (CoA), a coenzyme needed for the breakdown of carbohydrates, fatty acids, and amino acids, as well as for the modification of proteins and the synthesis of neurotransmitters, steroid hormones, and hemoglobin.
-Pantothenic acid is also needed for the activity of acyl carrier protein, which is needed for the synthesis of cholesterol and fatty acids
Pantothenic Acid Deficiency
- The wide distribution of pantothenic acid in foods makes deficiency rare in humans.
Recommended Pantothenic Acid Intake
- There is no RDA for pantothenic acid, but the AI has been set based on the amount sufficient to replace urinary losses.
Pantothenic Acid Toxicity
- Pantothenic acid is relatively nontoxic.
-Vitamin B6 is particularly important for amino acid and protein metabolism
-Vitamin B6 was identified when a deficiency syndrome was discovered that did not respond to thiamin or riboflavin supplementation.
-Vitamin B6 is easily destroyed by exposure to heat and light and is easily lost in processing
Vitamin B6 in the Diet
- Food sources of vitamin B6 include chicken, fish, liver, and whole grains.
How Vitamin B6 Functions in the Body
- Vitamin B6 comprises a group of compounds including pyridoxal, pyridoxine, and pyridoxamine. All three forms can be converted into the active coenzyme form, pyridoxal phosphate
- Pyridoxal phosphate, the coenzyme form of vitamin B6, is needed for the activity of more than 100 enzymes involved in the metabolism of the energy-yielding macronutrients.
- Vitamin B6 is a coenzyme for transamination, deamination, and decarboxylation reactions, and is therefore particularly important for amino acid metabolism.
-Both vitamin B6 and vitamin B12 (discussed later) are needed to synthesize and maintain the mylein coating on nerve cells. Myelin is essential for normal nerve transmission.
Vitamin B6 Deficiency
- Vitamin B6 deficiency causes neurological symptoms, anemia due to impaired hemoglobin syn-thesis, and poor immune function.
How Vitamin B6 Status is Related to Cardiovascular Disease
- Low levels of vitamin B6 can elevate levels of homocysteine, which can increase the risk of cardiovascular disease. On the other hand, good levels of B6 can can decrease cardiovascular disease by reducing levels of homocysteine
Recommended Vitamin B6 Intake
- The RDA is set at the level that is necessary to maintain adequate blood concentrations of the active coenzyme pyridoxal phosphate.
Vitamin B6 Toxicity and Supplements
- No adverse effects have been associated with high intakes of vitamin B6 from foods, but large doses found in supplements can cause serious toxicity symptoms.
Can Vitamin B6 Alleviate Carpal Tunnel Syndrome?
- Even though vitamin B6 is essential for nerve function, research indicates that vitamin B6 does not alleviate carpal tunnel syndrome.
Does Vitamin B6 Prevent Premenstrual Syndrome?
- More research is needed to confirm that vitamin B6 supplements are safe and effective for treating PMS.
Will Vitamin B6 Boost Immunity?
- Since elderly individuals frequently have low intakes of vitamin B6, it is unclear whether the beneficial effects of supplements due to an improvement of vitamin B6 status or immune system stimulation.
Folate (Folic Acid)
-Folate and folacin are general terms for compounds that have chemical structures and nutritional properties similar to those of folic acid (Figure 8.21). The chemical name for folate is pteroylglutamic acid.
Folate in the Diet and the Digestive Tract
- Excellent dietary sources of folate include liver, yeast, asparagus, oranges, legumes, and fortified grain products.
- About 50% of the folate in food is absorbed whereas the bioavailability of folic acid is nearly 100%.
How Folate Functions in the Body
-Folate is necessary for the synthesis of DNA, so it is especially important for rapidly dividing cells.
-Folate coenzymes are needed for the synthesis of DNA and the metabolism of some amino acids. Before a cell divides, its DNA must replicate. Therefore, the role of folate in DNA synthesis makes it particularly important in tissues where cells are rapidly dividing such as bone marrow, where red blood cells are made, intestines, and skin and during periods of rapid growth, such as early in embryonic life
- Groups at risk for folate deficiency include pregnant women and premature infants because of their rapid rate of cell division and growth, the elderly because of their limited intake of foods high in folate, alcoholics as alcohol inhibits folate absorption, and tobacco smokers as smoke inacti-vates folate in the cells lining the lungs.
Why Folate Deficiency Causes Anemia
- When folate is deficient, cells in the bone marrow that develop into red blood cells cannot replicate their DNA and so cannot divide. Instead, they just grow bigger.
- These large immature cells are known as megaloblasts and can be converted into large red blood cells called macrocytes. The result is that fewer mature red blood cells are produced and the oxygen-carrying capacity of the blood is reduced. This condition is called megaloblastic or macrocytic anemia
How Folate Is Related to the Risk of Neural Tube Defects
- Low levels of folate before and during early pregnancy are associated with an increased incidence of neural tube defects, such as spina bifida and anecephaly, in the offspring.
- Neural tube close is complete by 28 days after conception; therefore, folate status should be ade-quate even before a pregnancy begins.
How Folate Is Related to the Risk of Cardiovascular Disease
- Low intakes of folate have been associated with an increased risk of cardiovascular disease due to its role in converting homocysteine to methionine.
-Although supplementation with folic acid and vitamins B6 and B12 lowers homocysteine levels, it has not been shown to reduce the risk of cardiovascular disease. Although deficiency resulted in increased homocysteine levels has been shown to increase cardiovascular disease
How Folate Is Related to Cancer
- The relationship between folate and cancer is complicated and somewhat inconclusive. Speculated that it decreases risk of cancer but once cancer is formed then it increases risk given that it aids in cellular division thus deficiency decreases spread of cancer once you have cancer
Recommended Folate Intake
- The RDA for folate is expressed in dietary folate equivalents, which take in account the varying rates of absorption between folate and folic acid.
- The RDA for folate during pregnancy is increased 50% to provide for the increase in cell divi-sion.
Meeting Folate Needs
- Women of childbearing age may need to take a supplement.
- The Daily Value is expressed as micrograms of total folate, and not as micrograms of dietary fo-late equivalents.
- Although there is no known folate toxicity, a high intake of folate may mask the early symptoms of vitamin B12 deficiency, allowing it to go untreated and resulting in irreversible nerve damage.
-Vitamin B12 was discovered when individuals with anemia didn't respond to iron treatments.
- Vitamin B12 is found almost exclusively in animal products.
- While the bacteria in the human colon produce vitamin B12, it cannot be absorbed.
- Diets that do not include animal products must include supplements or foods fortified with vitamin B12 in order to meet needs.
Vitamin B12 in the Digestive Tract
-The vitamin B12 naturally present in food is bound to proteins and must be released before it can be absorbed. In the stomach, acid and the protein-digesting enzyme pepsin unfold and begin to break down proteins, releasing the vitamin B1
- The absorption of vitamin B12 from food requires adequate levels of stomach acid, intrinsic factor, and pancreatic secretions.
- Vitamin B12 is secreted in bile, but most of this is reabsorbed rather than being lost in the feces; therefore, vitamin B12 deficiency symptoms are slow to appear.
How Vitamin B12 Functions in the Body
- Vitamin B12 is needed for the metabolism of folate and fatty acids and to maintain the insulting layer of myelin surrounding nerves.
-This reaction is necessary for the maintenance of healthy myelin, which insulates nerves and is essential for normal nerve transmission (see Figure 8.19). A second vitamin B12-dependent reaction synthesizes the amino acid methionine from homocysteine. This reaction also requires folate (see Figure 8.20).
Vitamin B12 Deficiency
- The body stores and reuses vitamin B12 more efficiently than it does most other water-soluble vitamins, so deficiency is typically caused by poor absorption rather than by low intake alone.
-Symptoms of vitamin B12 deficiency include an increase in blood homocysteine levels and macrocytic, megaloblastic anemia that is indistinguishable from that seen in folate deficiency. This anemia occurs because vitamin B12 is needed to convert folate into the form that is active for DNA synthesis
-Vitamin B12 deficiency causes a folate deficiency because it prevents folate from being converted into the active form that is needed for DNA synthesis.
-Lack of vitamin B12 causes a secondary folate deficiency and consequently megaloblastic anemia
-When absorption is impaired, neither dietary vitamin B12 nor the vitamin B12 secreted in the bile is absorbed, so deficiency symptoms appear more rapidly. This occurs both in individuals with pernicious anemia and in those with atrophic gastritis.
If you were deficient in vitamin B12 but took large amounts of folic acid from supplements, would you develop macrocytic anemia? Why or why not?
-If individuals with vitamin B12 deficiency consume enough folate, they will not develop anemia, which is an easily identified and reversible symptom of vitamin B12 deficiency (see Figure 8.27). Without this symptom, diagnosis can be delayed, allowing more serious and irreversible symptoms, such as nerve damage, to progress.
Why Pernicious Anemia Causes B12 Deficiency
-Pernicious anemia is the major cause of severe vitamin B12 deficiency. It is an autoimmune disease in which the parietal cells in the stomach that produce intrinsic factor are destroyed. Without intrinsic factor, vitamin B12 cannot be absorbed normally.
How Atrophic Gastritis Causes B12 Deficiency
- When stomach acid is reduced (as that seen in those with atrophic gastritis), the enzymes that release vitamin B12 bound to food protein doesn't release it.
-Atrophic gastritis is an inflammation of the stomach lining that results in a reduction in stomach acid and bacterial overgrowth. When stomach acid is reduced, the enzymes that release vitamin B12 that is bound to food protein cannot function properly and the bound vitamin B12 cannot be released and absorbed.
- Vegans are at higher risk for B12 deficiency as they don't eat animal products.
Why Supplemental Folic Acid Can Mask Vitamin B12 Deficiency
- If individuals with vitamin B12 deficiency consume enough folate, they will not develop the anemia, which is an easily identified and reversible symptom of vitamin B12 deficiency.
Recommended Vitamin B12 Intake
- The RDA is set to maintain normal red blood cell parameters and normal blood concentrations of vitamin B12.
Vitamin B12 Toxicity and Supplements
- No toxic effects have been reported with excess vitamin B12 intakes of up to 100 micrograms per day from food or supplements.
- Obtaining enough Vitamin C, or ascorbic acid, has been an issue for armies for centuries.
-The vitamin C deficiency disease scurvy was the scourge of armies, navies, and explorers throughout history.
-The reason obtaining enough vitamin C, also known as ascorbic acid or ascorbate, has been a particular problem for armies and explorers is that fresh fruits and vegetables are its main sources; these foods spoil quickly and don't transport well on long voyages.
Vitamin C in the Diet
- The best food sources of vitamin C are citrus fruits, strawberries, and cantaloupe.
-Citrus fruits, such as oranges, lemons, and limes, are excellent sources of vitamin C.
- Vitamin C is unstable and is destroyed by oxygen, light, and heat, so it is readily lost in cooking.
How Vitamin C Functions in the Body
- Vitamin C donates electrons in biochemical reactions, including those needed for the synthesis and maintenance of connective tissue.
-It also helps maintain the immune system and aids in the absorption of iron.
Vitamin C and Collagen Synthesis
- Collagen is the protein that forms the base of all connective tissue in the body.
- Reactions requiring vitamin C are essential for the formation of bonds that hold adjacent collagen strands together and give the protein strength and stability.
-The inability to form healthy collagen prevents wounds from healing normally and causes bone and joint aches, bone fractures, and improperly formed and loose teeth (i.e. symptoms of scurvy)
Vitamin C as an Antioxidant
- Antioxidants protect against oxidative damage, which is damage caused by reactive oxygen molecules.
- Oxidative stress refers to a serious imbalance between the amounts of reactive oxygen molecules and the availability of antioxidant defenses. Oxidative stress has been related to the aging process as well as to the development of cancer and heart disease.
How Antioxidants Work
- Antioxidants act by destroying reactive oxygen molecules before they can do damage.
-Reactive oxygen molecules such as free radicals come from environmental sources such as air pollution or cigarette smoke as well as from normal oxygen-requiring reactions inside the body. Free radicals cause damage by snatching electrons from DNA, proteins, carbohydrates, or unsaturated fatty acids.
How Vitamin C Functions as an Antioxidant
- Vitamin C donates an electron to neutralize superoxide radicals and free radicals before they can damage lipids and DNA.
-Vitamin C functions as an antioxidant by donating electrons to neutralize free radicals so that they are no longer damaging.
Vitamin C Deficiency
- Vitamin C deficiency, called scurvy, is characterized by poor wound healing, bleeding, and other symptoms related to the improper formation and maintenance of collagen.
Recommended Vitamin C Intake
- The recommendations for vitamin C intake are based on the amount needed to maximize concentrations in neutrophils, a type of white blood cell, with minimal excretion in the urine.
-In people prone to kidney stones, excess vitamin C can increase stone formation
Vitamin C Toxicity and Supplements
- Vitamin C is generally considered nontoxic.
Do Vitamin C Supplements Cure the Common Cold?
- Vitamin C supplements won't prevent you from catching a cold, but they may help you recover faster.
Can Vitamin C Supplements Protect against Cardiovascular Disease?
- Data thus far from epidemiology and human intervention trials have provided little evidence to support the use of vitamin C supplements in preventing atherosclerosis in humans.
Do Vitamin C Supplements Protect against Cancer?
- Although controlled trials have not found any benefits of vitamin C in the treatment of patients with advanced cancer, there is evidence supporting a role for vitamin C in cancer prevention.
- Choline is considered an essential nutrient, but is not currently classified as a vitamin. The best dietary sources of choline are egg yolks and meats.
-It is needed for the synthesis of the neurotransmitter acetylcholine, the structure and function of cell membranes, lipid transport, and homocysteine metabolism.
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