Chapter 1 – Title of Chapter - Nutrition Gardener
Chapter 10 – The Water-Soluble Vitamins: B Vitamins and Vitamin C
Learning Objectives
1. Define a vitamin and classify vitamins as water soluble or fat soluble.
2. List the B vitamins and identify the major functions of each vitamin in the body.
3. Identify the non-B vitamins.
4. Describe the role of B vitamins in metabolism.
5. List a major food source of each of the B vitamins.
6. Identify the major deficiency disease associated with each B vitamin.
7. List the major uses of vitamin C in the body.
8. Identify the vitamin C requirement of the body and factors that may increase this requirement.
9. Identify the signs and symptoms of vitamin C deficiency and toxicity.
10. Identify major food sources of vitamin C.
11. Discuss the arguments for and against the use of vitamin supplements.
12. Explain the Dietary Supplement Health and Education Act of 1994 and how the consumer can use the act in the selection of a nutrient supplement.
I. The Vitamins—An Overview
Vitamins differ from carbohydrate, fat, and protein in structure, function, and food contents. Vitamins are similar to the energy-yielding nutrients in that they are vital to life, organic, and available from foods. Both deficiencies and excesses of the vitamins can affect health.
A. Bioavailability is the rate and extent that a nutrient is absorbed and used.
B. Precursors, also known as provitamins, are consumed in an inactive form and become active vitamins in the body.
C. The organic nature of vitamins means they can be destroyed by exposure to light, oxidation, cooking, and storage. There are methods used to minimize nutrient losses.
1. Refrigerate fruits and vegetables.
2. Store cut fruits and vegetables in airtight wrappers or closed containers and refrigerate.
3. Clean fruits and vegetables before they are cut.
4. Use a microwave, steam, or simmer in small amounts of water. Save cooking water for other uses. Avoid high temperatures and long cooking times.
D. Solubility
1. Water-soluble vitamins (B vitamins and vitamin C) are absorbed directly into the blood and travel freely.
a. Circulate freely.
b. Excreted in urine.
2. Fat-soluble vitamins (vitamins A, D, K and E) are absorbed first into the lymph, then the blood. Many require protein carriers.
a. Stored in cells associated with fat.
b. Less readily excreted.
E. Toxicity
1. Water-soluble vitamins can reach toxic levels with supplement use.
2. Fat-soluble vitamins are likely to reach toxic levels with supplement use.
3. DRI Committee has established Tolerable Upper Intake Levels for niacin, vitamin B6, folate, choline, and vitamin C.
II. The B Vitamins—As Individuals
The B vitamins are very active in the body. Several of the B vitamins form part of the coenzymes that assist enzymes in the release of energy. Other B vitamins participate in metabolism and cell multiplication. Recommendations for the B vitamins come from RDA, AI, and Tolerable Upper Intake Levels. There are deficiencies, toxicities, and food sources that are unique for each vitamin.
A. Thiamin (Vitamin B1) – Thiamin is involved in energy metabolism as part of the coenzyme thiamin pyrophosphate (TPP).
1. Thiamin Recommendations
a. RDA Men: 1.2 mg/day.
b. RDA Women: 1.1 mg/day.
2. Thiamin Deficiency and Toxicity
a. Deficiency symptoms
1. Enlarged heart and possible cardiac failure.
2. Muscular weakness.
3. Apathy, poor short-term memory, confusion, and irritability.
4. Anorexia and weight loss.
b. Wernicke-Korsakoff syndrome is a severe deficiency that develops in those who abuse alcohol.
c. Deficiency results in the disease beriberi.
1. Wet beriberi presents with edema.
2. Dry beriberi presents with muscle wasting.
d. No reported toxicities.
3. Thiamin Food Sources
a. Whole-grain, fortified or enriched grain products.
b. Moderate amounts in all foods.
c. Pork.
4. Other Information
a. Steaming and microwaving are cooking methods that conserve thiamin.
b. Thiamin leaches into water with boiling or blanching.
c. The vitamin is easily destroyed by heat.
B. Riboflavin (Vitamin B2) –Riboflavin is involved in energy metabolism. Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are the coenzyme forms.
1. Riboflavin Recommendations
a. RDA Men: 1.3 mg/day.
b. RDA Women: 1.1 mg/day.
2. Riboflavin Deficiency and Toxicity
a. Deficiency symptoms
1. Sore throat and cracks and redness at the corners of the mouth.
3. Painful, smooth, and purplish red tongue.
4. Skin lesions covered with greasy scales.
b. Deficiency disease is ariboflavinosis.
c. No reported toxicities.
3. Riboflavin Food Sources
a. Milk products, including yogurt and cheese.
b. Whole-grain, fortified, and enriched grain products.
c. Liver.
4. Other information
a. Easily destroyed by ultraviolet light and irradiation.
b. Not destroyed by cooking.
C. Niacin (Vitamin B3) – Niacin is involved in the metabolism of glucose, fat, and alcohol. Nicotinamide adenine dinucleotide (NAD), and NADP, the phosphate form of NAD, are the coenzyme forms.
1. Niacin Recommendations
a. The body can obtain niacin from dietary niacin and dietary tryptophan (60 mg of dietary tryptophan = 1 mg niacin); therefore niacin intake is measured in niacin equivalents (NE).
b. RDA Men: 16 NE/day.
c. RDA Women: 14 NE/day.
d. Upper level of 35 mg/day for adults.
2. Niacin Deficiency
a. A deficiency of niacin results in the disease pellagra.
b. Deficiency symptoms
1. Diarrhea, abdominal pain, and vomiting.
2. Inflamed, swollen, smooth, and bright red tongue.
3. Depression, apathy, fatigue, loss of memory, and headache.
4. Rash when exposed to sunlight.
3. Niacin Toxicity
a. Niacin flush dilates the capillaries and may be painful.
b. Toxicity symptoms
1. Painful flush, hives, and rash.
2. Excessive sweating.
3. Blurred vision.
4. Liver damage.
5. Impaired glucose tolerance.
4. Niacin Food Sources
a. Milk, eggs, meat, poultry, and fish.
b. Whole-grain and enriched breads and cereals.
c. Nuts and all protein-containing foods.
5. Other Information
a. Also called nicotinic acid, nicotinamide, and niacinamide.
b. The amino acid tryptophan is the precursor.
c. The vitamin can be lost from foods when it leaches into water.
d. Resistant to heat.
D. Biotin – As part of a coenzyme used in energy metabolism, biotin assists in glycogen synthesis, fat synthesis, and amino acid metabolism.
1. Biotin Recommendations – AI Adults: 30 (g/day.
2. Biotin Deficiency and Toxicity
a. Deficiencies are rare.
b. Deficiency symptoms
1. Depression, lethargy, and hallucinations.
2. Numb or tingling sensation in the arms and legs.
3. Red, scaly rash around the eyes, nose, and mouth.
4. Hair loss.
c. Biotin can be bound with an egg-white protein called avidin.
d. No reported toxicities.
3. Biotin Food Sources
a. Widespread in foods.
b. Organ meats, egg yolks, and fish.
c. Soybeans.
d. Whole grains.
4. Biotin can also be synthesized by intestinal bacteria.
E. Pantothenic Acid – Pantothenic acid is involved in energy metabolism as a part of coenzyme A.
1. Pantothenic Acid Recommendations – AI Adults: 5 mg/day.
2. Pantothenic Acid Deficiency and Toxicity
a. Deficiency is rare.
b. Deficiency symptoms
1. Vomiting, nausea, and stomach cramps.
2. Insomnia and fatigue.
3. Depression, irritability, restlessness, and apathy.
4. Hypoglycemia and increased sensitivity to insulin.
5. Numbness, muscle cramps, and inability to walk.
c. No reported toxicities.
3. Pantothenic Acid Food Sources
a. Widespread in foods.
b. Chicken, beef, liver, and egg yolks.
c. Potatoes, tomatoes, and broccoli.
d. Whole grains and oats.
e. Can be destroyed by freezing, canning, and refining.
F. Vitamin B6 (pyridoxine, pyridoxal, or pyridoxamine) – The coenzyme forms of vitamin B6 (pyridoxal phosphate [PLP] and pyridoxamine phosphate [PMP]) are involved in amino and fatty acid metabolism, the conversion of tryptophan to niacin or serotonin, and the production of red blood cells.
1. Vitamin B6 Recommendations – RDA Adults 19-50 years: 1.3 mg/day.
2. Vitamin B6 Deficiency
a. Deficiency symptoms
1. Scaly dermatitis.
2. Anemia – small cell type.
3. Depression, confusion, and convulsions.
b. Alcohol destroys the vitamin.
c. Isoniazid (INH) drug used for tuberculosis acts as an antagonist.
3. Vitamin B6 Toxicity
a Toxicity symptoms
1. Depression, fatigue, irritability, and headaches.
2. Nerve damage causing numbness and muscle weakness leading to inability to walk.
3. Convulsions.
4. Skin lesions.
b. Upper level for adults: 100 mg/day.
4. Vitamin B6 Food Sources
a. Meats, fish, poultry, and liver.
b. Legumes and soy products.
c. Non-citrus fruits.
d. Fortified cereals.
e. Potatoes and other starchy vegetables.
5. Other Information
a. Easily destroyed by heat.
b. Vitamin B6 appears to be ineffective in curing carpal tunnel syndrome.
G. Folate (folic acid, folacin, pteroylglutamic acid-PGA) – Folate is involved in the synthesis of DNA and the formation of new cells. The coenzymes THF (tetrahydrofolate) and DHF (dihydrofolate) require vitamin B12 to function correctly.
1. Folate Recommendations
a. RDA Adults: 400 (g/day.
b. Dietary Folate Equivalents (DFE) is a calculation that accounts for the bioavailability differences between folate from foods and folate from supplements.
c. There are higher recommendations for pregnant women.
2. Folate and Neural Tube Defects
a. Neural tube defects include spina bifida and anencephaly.
b. Women of childbearing age should eat folate-rich foods and folate-fortified foods and take folate supplements containing 0.4 mg (400 microgram) of folate daily to ensure proper development of the neural tube.
c. Pregnant women should take folate supplements.
3. Folate and Heart Disease
a. High levels of homocysteine and low levels of folate increase risk of heart disease.
b. Folate breaks down homocysteine.
4. Folate may help to prevent cancer, but may also promote cancer growth once cancer has developed.
5. Folate Deficiency
a. Deficiency symptoms
1. Macrocytic anemia, also called megaloblastic anemia – large cell type.
2. Smooth, red tongue.
3. Mental confusion, weakness, fatigue, irritability, and headaches.
4. Shortness of breath.
5. Elevated homocysteine levels.
b. Most vulnerable of all the vitamins to interactions with medications.
1. Anticancer drugs.
2. Antacids and aspirin.
3. Oral contraceptives.
6. Folate Toxicity
a. Masks vitamin B12 deficiency symptoms.
b. Upper level for adults: 1000 (g/day.
7. Folate Food Sources
a. Fortified grains.
b. Leafy green vegetables.
c. Legumes and seeds.
d. Liver.
8. Other Information
a. Easily destroyed by heat and oxygen.
H. Vitamin B12 (Cobalamin) – Vitamin B12 is involved in the synthesis of new cells, maintains nerve cells, reforms folate coenzymes, and helps break down some fatty acids and amino acids. Methylcobalamine and deoxyadenosylcobalamin are the coenzyme forms.
1. Vitamin B12 Recommendations
a. RDA Adults: 2.4 (g/day.
2. Vitamin B12 Deficiency and Toxicity
a. Deficiency Symptoms
1. Anemia – large cell type.
2. Fatigue and degeneration of peripheral nerves progressing to paralysis.
3. Sore tongue, loss of appetite, and constipation.
b. Atrophic gastritis in older adults destroys stomach cells, which diminishes intrinsic factor and hydrochloric acid production.
c. Deficiency disease is called pernicious anemia.
d. No known toxicities
3. Vitamin B12 Food Sources.
a. Meat, fish, poultry, and shellfish.
b. Milk, cheese, and eggs.
c. Fortified cereals.
4. Other Information
a. Binds with intrinsic factor in the small intestine for absorption.
b. Easily destroyed by microwave cooking.
I. Vitamin-Like Compounds
1. Choline – Choline is involved in the synthesis of acetylcholine and lecithin.
a. Choline recommendations
1. AI Men: 550 mg/day.
2. AI Women: 425 mg/day.
b. Choline deficiency and toxicity
1. Deficiencies are rare.
2. Deficiency symptom is liver damage.
3. Toxicity symptoms
a. Body odor and sweating.
b. Salivation.
c. Reduced growth rate.
d. Low blood pressure.
e. Liver damage.
4. Upper level for adults: 3500 mg/day.
c. Choline food sources – Milk, liver, eggs, and peanuts.
2. Inositol and Carnitine
a. Inositol is made from glucose and is part of the cell membrane structure.
b. Carnitine is made from lysine and transports long-chain fatty acids to be oxidized.
3. Non-vitamins are substances needed by other forms of life but not human beings. They can be potentially dangerous when used by humans.
III. The B Vitamins—In Concert
The B Vitamins are interdependent. The presence of one may affect the absorption, metabolism, and excretion of another. A deficiency of one may affect the functioning or deficiency of another. A variety of foods from each food group will provide an adequate supply of all the B vitamins.
A. B Vitamin Roles
1. Coenzymes involved directly or indirectly with energy metabolism.
2. Facilitate energy-releasing reactions.
3. Build new cells to deliver oxygen and nutrients for energy reactions.
B. B Vitamin Deficiencies
1. Deficiencies rarely occur singly except for beriberi and pellagra.
2. Can be primary or secondary causes.
3. Glossitis and cheilosis are two symptoms common to B vitamin deficiencies.
4. Symptoms that individuals experience are not necessarily related to a vitamin deficiency.
C. B vitamin toxicities can occur with supplements.
D. B Vitamin Food Sources
1. Grains group provides thiamin, riboflavin, niacin and folate.
2. Fruits and vegetables provide folate.
3. Meat group provides thiamin, niacin, vitamin B6, and vitamin B12.
4. Milk group provides riboflavin and vitamin B12.
IV. Vitamin C (antiscorbutic factor is the original name for vitamin C)
Vitamin C serves as a cofactor to facilitate the action of an enzyme and also serves as an antioxidant.
A. Vitamin C Roles
1. As an Antioxidant
a. Defends against free radicals.
b. Protects tissues from oxidative stress.
2. As a Cofactor in Collagen Formation
a. Collagen is used for bones and teeth, scar tissue, and artery walls.
b. Works with iron to form hydroxiproline, which is needed in collagen formation.
3. As a Cofactor in Other Reactions
a. Hydroxylation of carnitine.
b. Converts tryptophan to neurotransmitters.
c. Makes hormones.
4. Vitamin C needs increase during body stress, i.e. infections, burns, extremely high or low temperatures, heavy metal intakes, certain medications, and smoking.
5. In the Prevention and Treatment of the Common Cold
a. Some relief of symptoms.
b. Vitamin C deactivates histamine like an antihistamine.
6. Role in disease prevention is still being researched.
B. Vitamin C Recommendations
1. RDA Men: 90 mg/day.
2. RDA Women: 75 mg/day.
3. Smokers: +35 mg/day.
C. Vitamin C Deficiency
1. Deficiency disease is called scurvy.
2. Deficiency symptoms
a. Anemia – small cell type.
b. Atherosclerotic plaques and pinpoint hemorrhages.
c. Bone fragility and joint pain.
d. Poor wound healing and frequent infections.
e. Bleeding gums and loosened teeth.
f. Muscle degeneration and pain, hysteria, and depression.
g. Rough skin and blotchy bruises.
[pic] D. Vitamin C Toxicity
1. Toxicity symptoms
a. Nausea, abdominal cramps, diarrhea, headache, fatigue, and insomnia.
b. Hot flashes and rashes.
c. Interference with medical tests, creating a false positive or a false negative.
d. Aggravation of gout symptoms, urinary tract infections, and kidney stones.
2. Upper level for adults: 2000 mg/day.
E. Vitamin C Food Sources
1. Citrus fruits, cantaloupe, strawberries, papayas, and mangoes.
2. Cabbage-type vegetables, dark green vegetables like green peppers and broccoli, lettuce, tomatoes, and potatoes.
F. Other information
1. Also called ascorbic acid.
2. Easily destroyed by heat and oxygen.
V. Highlight: Vitamin and Mineral Supplements
Many people take dietary supplements for dietary and health insurance. Some take multinutrient pills daily. Others take large doses of single nutrients. A valid nutrition assessment by professionals determines the need for supplements. Self-prescribed supplementation is not advised. There are many arguments for and against supplements.
A. Arguments for Supplements
1. Correct Overt Deficiencies.
2. Support Increased Nutrient Needs.
3. Improve Nutrition Status.
4. Improve the Body’s Defenses.
5. Reduce Disease Risks.
6. Who Needs Supplements?
a. People with nutritional deficiencies.
b. People with low energy intake – less than 1600 kcalories per day.
c. Vegans and those with atrophic gastritis need vitamin B12.
d. People with lactose intolerance, milk allergies, or inadequate intake of dairy foods need calcium.
e. People in certain stages of the life cycle.
1. Infants need iron and fluoride.
2. Women of childbearing age and pregnant women need folate and iron.
3. Elderly need vitamins B12 and D.
f. Those with limited sun exposure and poor milk intake need vitamin D.
g. People with diseases, infections, or injuries, and those who have had surgery that affects nutrient digestion, absorption, or metabolism.
h. People taking medications that interfere with the body’s use of specific nutrients.
B. Arguments against Supplements
1. Toxicity.
2. Life-Threatening Misinformation.
3. Unknown Needs.
4. False Sense of Security.
5. Other Invalid Reasons:
a. Belief that food supply and soil contain inadequate nutrients.
b. Belief that supplements provide energy.
c. Belief that supplements enhance athletic performance or lean body mass without physical work or faster than work alone.
d. Belief that supplements will help a person cope with stress.
e. Belief that supplements can prevent, treat, or cure conditions.
6. Bioavailability and Antagonistic Actions
a. Micronutrients from supplements compete for absorption – e.g. zinc, iron, calcium, magnesium.
b. Some can interfere with each other’s metabolism – e.g. beta-carotene, vitamin E.
C. Selection of Supplements
1. What form do you want?
2. What vitamins and minerals do you need?
a. Do not exceed Tolerable Upper Intake Levels.
b. Be careful about greater that 10 mg of iron.
3. Are there misleading claims?
a. Ignore organic or natural claims.
b. Avoid products that make high potency claims.
c. Watch fake preparations.
d. Be aware of marketing ploys.
e. Be aware of preparations that contain alcohol.
f. Be aware of the latest nutrition buzzwords.
g. Internet information is not closely regulated.
4. What about the cost?
a. Local or store brands may be just as good as nationally advertised brands.
D. Regulation of Supplements
1. Nutritional labeling for supplements is required.
2. Labels may make nutrient claims according to specified criteria.
3. Labels may claim that lack of a nutrient can cause a deficiency disease and include the prevalence of that disease.
4. Labels may make health claims that are supported by significant scientific agreement.
5. Labels may claim to diagnose, treat, cure, or relieve common complaints but not make claims about specific diseases.
6. Labels may make structure-function claims if accompanied by Food And Drug Administration (FDA) disclaimer.
a. Role a nutrient plays in the body.
b. How the nutrient performs its function.
c. How consuming the nutrient is associated with general well-being.
Case Study[1]
Samuel is a 63-year-old single man who works full time in a food processing plant. He has a history of esophageal cancer which was treated successfully with anti-cancer drugs and surgery four years ago. His weight has been stable at 135 pounds until the past 6 months, in which he has experienced an involuntary weight loss of 10 pounds. He is 67 inches tall and his current BMI is 19.5. He complains of a poor appetite and being overly weak and tired. His usual diet is fairly consistent. He states he rarely eats breakfast because he starts work at 6 a.m. He eats two deli meat sandwiches, “usually pastrami or salami,” and a soda at 10 a.m. and may eat a candy bar in the afternoon when he gets off work. He often prepares frozen dinners or pizza at home in the evening and routinely drinks “about 2 or 3 beers” before going to bed. Occasionally he will cook a roast and mashed potatoes. He occasionally will have milk with cereal but rarely eats vegetables or fruit. He would like to know which vitamin supplement will give him energy.
1. How would you explain the function of vitamins in response to Samuel’s request?
2. What are some indications that Samuel’s diet may be low in thiamin?
3. Using information from Figure 10-4, list one or two good sources of thiamin from each of the foods groups that Samuel could add to his diet.
4. What other vitamins would you suspect to be deficient in Samuel’s diet? Why?
5. Based on his medical and diet history, explain why Samuel may be at risk for folate deficiency.
6. Based on his medical history and information in this chapter, how would you advise Samuel regarding his complaints of fatigue and weight loss?
7. Would you recommend a daily multivitamin supplement for Samuel based on the history he has provided? Why or why not?
Answer Key:
1. Vitamin supplements do not provide as many benefits as vitamin-rich foods. They do not provide energy but assist the enzymes that release energy from carbohydrates, fats, and proteins in foods.
2. His calorie intake is low; he derives much of his energy needs from empty-calorie foods and beverages. He drinks an excessive amount of alcohol.
3. Fortified corn flakes, flour tortilla, baked potato with skin, tomato juice, milk, yogurt, pinto beans, peanut butter, pork chop, soy milk, watermelon, orange.
4. Riboflavin due to limited milk and vegetable intake. Vitamin C due to limited fruit and vegetable intake.
5. Some anti-cancer drugs interfere with folate metabolism; limited intake of fruits and vegetables; excess alcohol intake.
6. Determine whether his symptoms are nutritional or non-nutritional in cause. Because of his history of cancer, he should see his physician for tests to determine the cause of his tiredness.
7. Yes; he has a limited diet, routinely low in B vitamins and vitamin C, with increased needs due to his chronic alcohol use. All these vitamins would be provided in reasonable amounts in a daily multivitamin with little risk for toxicity.
Critical Thinking Questions
1. Outline the differences between macronutrients (carbohydrates, fats, and proteins) and vitamins.
Answer: There are many to discuss:
Structure: Vitamins are individual units, as opposed to macronutrients, which can be broken down further into individual units that provide energy. Vitamins do not provide energy per se but are involved in metabolic pathways that provide energy. Vitamins are utilized for metabolic pathways and several other functions and they are available readily.
Function: Vitamins do not yield any energy but do help in metabolic pathways that yield energy. Many of the B vitamins assist enzymes in their functions in the metabolic pathways.
Amount in Food Content: Vitamins are needed in minimal amounts as opposed to the large amounts of macronutrients required. While the water-soluble and fat-soluble vitamins are very necessary, as are macronutrients, the absolute amounts are much less.
Bioavailability: While macronutrients are generally stable in foods and relatively easily absorbed and utilized by the body for energy, micronutrients retain many issues that impact their bioavailability. For example, heat and light can destroy many of the B vitamins during food preparation or storage.
Precursors: Some of the water-soluble vitamins are precursors to reactions or are provitamins. Macronutrients do not have this function. This again gets back to their roles in metabolic pathways.
Organic Nature: Macronutrients are of course organic. Vitamins, however, can be destroyed by light, and many types of handling that the macronutrients are not susceptible to. While proteins are susceptible to denaturing by high heat, vitamins, particularly water-soluble vitamins, are very susceptible to heat, sunlight, and other factors. Whereas macronutrients are normally broken down in the body for use, and hence denaturing of proteins is a normal part of digestion, vitamins must retain their chemical structures as they are absorbed or they cannot perform their functions.
Solubility: Water-soluble vitamins are hydrophilic. This differs from the lipids but not from the proteins and carbohydrates.
Toxicity: While most water-soluble vitamins are not believed to pose a toxicity risk, there is some ability for the body to store these vitamins. The macronutrients (proteins, carbohydrates, and fatty acids), for the most part, are not able to cause toxic effects to the body (protein has limited ability to cause toxic effects). Toxicity, however, is more common with the fat-soluble vitamins, which are stored extensively in adipose tissues.
2. The B vitamins are very important in many critical functions of the body, yet many clients perceive B vitamins in a much critical manner. How would you educate clients about the importance of B vitamins and their critical functions without confusing them?
Answer: The B vitamins have many different roles in reactions within the metabolic pathways.
Thiamin: This water-soluble vitamin is a vital part of thiamin pyrophosphate, a coenzyme that is very important for energy metabolism. This vitamin is very heat liable, and a deficiency causes beriberi. Thiamin is available in many foods, including fruits, vegetables, and meats.
Riboflavin: This water-soluble vitamin also functions as a coenzyme in many reactions in energy metabolism. Riboflavin is also very heat and sun labile and serves many functions in maintenance of the integrity of the membranes of the skin, eyes, and GI tract. Riboflavin is available in several foods including dairy products and meats.
Niacin: This is another important vitamin that functions as a coenzyme in many metabolic reactions. Without niacin, many of these reactions could not take place. Niacin deficiency is associated with pellagra, which is seldom seen in developed nations. Tryptophan is a precursor to niacin. Sources include proteins, whole grains, and nuts. Niacin has been prescribed for lowering cholesterol and can be quite effective. However, too much niacin can result in a hot-flash-like reaction referred to as “niacin flush” that causes considerable discomfort. Caution should be taken when considering a niacin supplement.
Biotin: This B vitamin also plays an important role in carbohydrate metabolism within the TCA cycle. While deficiencies are rare, there are instances where consumption of egg whites can cause a deficiency of biotin. Biotin is found in protein sources such egg yolks, liver, and soybeans.
Pantothenic Acid: Another important vitamin in metabolic pathways is pathothenic acid. This vitamin is part of coenzyme A and thus part of the TCA cycle. While the needs for this vitamin are not large, a deficiency can cause many issues in neurologic function. Sources of pantothenic acid are proteins and whole grains.
Vitamin B6: This vitamin is very important as a coenzyme that helps metabolize urea. Vitamin B6 also helps convert tryptophan to niacin and functions to activate neurotransmsmitters. This vitamin is very heat liable and can be stored in the muscles, making toxicity a possibility. Sources of vitamin B6 are protein sources as well as potatoes, green vegetables, and fruits.
Folate: This vitamin is a coenzyme for some of the most important metabolic functions, particularly with regard to DNA synthesis. Its importance has only been recognized in the last couple of decades. This vitamin helps prevent neural tube defects and (in some individuals) cancer. Sources include fruits and vegetables as well as legumes.
B12: This vitamin and folate are closely intertwined as B12 is required to convert folate to its active form. B12 is important for nervous system function and nerve cell maintenance. The need for B12 is very small and it can be recycled very effectively. Most deficiencies are related to absorption of the vitamin rather than intake. Given that sources of B12 are all animal-derived foods, vegans need fortified foods or supplementation of B12. Careful selection of food products, such as fortified soy milk, miso, and yeast can adequately provide enough B12 for an individual on a vegan diet.
Finally, it is important to understand the overall role of all the B vitamins within the metabolic pathways. Collectively, they help to ensure that the metabolic pathways function at an optimal level. As noted in Figure 10-14, the many B vitamins perform a multitude of activities as coenzymes, and without them, energy metabolism would not occur.
3. Discuss the roles of vitamin C.
Answer: Vitamin C serves in a multitude of roles within the body. It has long been known to relieve the symptoms of scurvy, which was rampant in the British Navy when sailors did not receive any citrus fruits. The role of ascorbic acid was later discovered. From that time, scientists were aware of the need for vitamin C.
For years, there has been a continued debate as to the need for additional vitamin C to prevent illness and to cure the common cold. Data continues to be inconsistent and many individuals rely on anecdotal reports. The only consistent finding is the need for additional vitamin C in smokers.
Another clearly-defined role for vitamin C is that of an antioxidant. Vitamin C does defend the body against free radicals that are produced by the body as a result of oxidative stress.
Vitamin C is a cofactor in the formation of collagen, an important material in formation of bones and teeth. Vitamin C is also a cofactor in other reactions involving transport of fatty acids for cell membrane synthesis, neurotransmitter transmission, and hormone production.
Vitamin C is found in many citrus fruits and green leafy vegetables.
4. Biochemistry and nutrition / dietetics:
All of the B vitamins are critical in playing a role in energy metabolism, most as coenzymes or cofactors. Without the B vitamins, energy metabolism would halt! The students simply need to explain the following:
Thiamin: Thiamin functions as the coenzyme thiamin pyrophosphate in the reaction that converts pyruvate to acetyl CoA. This conversion of a three-carbon to a two-carbon compound is required for the TCA cycle.
Riboflavin: Riboflavin also serves as a coenzyme and functions as an electron donor in FMN and FAD.
Niacin: The same holds true for niacin as NAD and NADP. Nicotinamide is very active in several areas of the metabolic cycles, including glycolysis and amino acid metabolism.
Vitamin B6: Vitamin B6 functions as a coenzyme as pyridoxal phosphate in critical reactions in glycolysis and in amino acid metabolism.
Folate: Folate or tetrahydrofolate requires B12 to activate it and serves as the coenzyme for one-carbon transfers. The result is the generation of the amino acid methionine.
B12: B12 and folate are intimately involved in a coupled reaction that involves the activation of folate, production of methionine, and synthesis of DNA.
Clearly, without B vitamins, energy metabolism as we know it would not exist; therefore, the study of nutrition and dietetics is well beyond cooking food. This is a field for research and education on the role of food in the body for energy production, protein synthesis, tissue repair, growth and development, recovery from illness and injury, and improvement of health, as well as many other areas. The student’s friend learned even more than anticipated today from their encounter with a nutrition and dietetics student, which of course, always happens!
5. Differentiate between water- and fat-soluble vitamins and discuss how a diet that is low in fat might impact vitamin absorption.
Answer: Water-soluble vitamins are vitamins that can be absorbed in an aqueous environment. In general, they are not stored in the body; however, vitamin B6 appears to have some ability to be stored in the muscle. There is little risk that the water-soluble vitamins that cannot be stored in the body will reach toxic levels. Because the body does not generally store these vitamins, water-soluble vitamins need to be replenished on a regular basis. Excess is excreted by the kidneys into the urine.
Fat-soluble vitamins require ingestion of fatty acids in order for the vitamin to be absorbed. Therefore, they are absorbed into the lymph before being transferred to the bloodstream. Because of their association with fatty acids, fat-soluble vitamins can be stored; as a result, they can reach toxic levels in the body, most particularly vitamin A. To rid the body of excessive stores, the person should consume less so that stores are reduced.
An individual that is consuming a low-fat diet may not be consuming enough fat to allow for absorption of fat-soluble vitamins, though in general, a low-fat diet would not preclude their absorption. The amount of fat in the diet can be very little; only two tablespoons of added oil a day is enough to provide for the body’s needs. However, if an individual is not consuming added fat and is avoiding all fat in their diet, as well as perhaps taking an over-the-counter medication such as alli, which works to excrete about 30% of the fat consumed, it may be conceivable that an individual (such as an anorexic) may need to be worked with nutritionally to aide in fat-soluble vitamin absorption. One tactic that can be taken is to rub monounsaturated or polyunsaturated fatty acids into the skin of the client, which will allow some to be absorbed over a short time. With vitamin supplementation, short-term results can be achieved for those clients that do not require immediate hospitalization.
Long term, with a client that has avoided any fat, it will be a matter of nutrition education, counseling, and patience to add a small amount of oil to the diet and supplement with fat-soluble vitamins.
6. There is much debate regarding the need for consumers to take vitamin and/or mineral supplements. As a nutrition professional, how would you advise a client (female who is 60 y/o and has no medical history, has no current medical problems, and takes no medications) that believes in and therefore insists on taking large doses of vitamin and mineral supplements to prevent disease?
Answer: A consumer’s desire to take a vitamin/mineral supplement is driven by many factors, many of which have little scientific evidence for validation. For the nutrition student, it is important to keep in mind that nutrition as a science is comparatively young, in relation to many of the other basic sciences, and in this regard, much is still being discovered. As a result, it is not unusual for foods such as broccoli or milk, etc. to be reported as having differing, sometimes contradictory benefits and disadvantages over a decade. These facts can often be confusing to the consumer. As a result, the vitamin and mineral supplement can be seen as a safe road in providing the necessary nutrients to a person’s body and protection of health status without the confusion.
In addition to the above consideration, present lifestyles are faster paced, stressed, and uncertain. Under these circumstances, an individual may find the added protection of a vitamin and mineral supplement some security from poor dietary choices and the impacts of stress on the body.
Stressors of an active world but also environmental stressors are also a concern, given their potential carcinogenic effects. Some individuals believe that diet alone cannot protect the body from all the carcinogens that surround individuals, and desire the added protection of vitamin and mineral supplements.
Additionally, some individuals grow into a culture where vitamin and mineral supplementation is part of their history and lifestyle. Supplementation is part of self-care that was perceived as enhancing the longevity of parents and grandparents and, therefore, is continued on as self-care for oneself.
Above are many considerations for the RD counseling a client that insists on taking large doses of vitamin and mineral supplements. Clearly there can be others that the students will discuss. The client may be afraid of illness or dying, have different types of paranoia, etc. These should all be considered when counseling a client such as this. In other words, what is the root of the desire or need for the supplementation, beyond a regular diet?
Dietary assessment is required as well as physical and biochemical assessment to acquire information on any physical illnesses or past histories. Medical background and history should be acquired as well. The assumption is that the client is asymptomatic and that this is simply a desire without physical rationale; therefore, the RD must deal with the psychological/mental concerns and work to have the client fill vitamin and mineral needs through diet.
The best approach here is to ask about the length of time this individual has been taking the supplements, and in what doses, and to have a very clear understanding of her diet and all medical information as well as the above information.
Given that she is not on any medications that would result in drug/supplement interactions, that is not a concern here.
This individual is in good health and may be taking the supplements because of a learned family history. Or, she may have begun this habit as she grew older and wanted to optimize her health status or as her dietary habits were changing. All things to be explored. That being said, because she is in good health, is not taking medications that would interact with the supplements, and has no medical history, this is a client that would benefit from nutrition education as to where the various vitamin and minerals can be found in foods and how foods can be prepared to optimize the micronutrient viability. Nutrition education with the client as to the role of the various vitamins and minerals would also be helpful. In this manner, the client is empowered to understand the role and source of the numerous vitamins and minerals in foods herself so that she is assured that she can provide her body with adequate nutrients. Beyond that, the RD should recommend a general multiple vitamin, thus working to move her client away from mega-doses of vitamins.
Having worked with clients in private practice for many years, I know that it may not always be realistic to stop clients from taking vitamin/mineral supplements. But, when one can empower the client enough in the area of foods, generally, the client will lower their dosage to a basic multivitamin supplement and avoid the mega dosing.
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