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Chapter 8THE WATER-SOLUBLE VITAMINS
Vitamin Talk Vitamins are organic compounds essential in
the diet to promote growth and health maintenance.
Water-soluble vitamins include the B vitamins and vitamin C.
Fat-soluble vitamins include A, D, E and K. B vitamins were originally thought to be one
chemical substance but are actually many different substances. That is the reason for B1, B2, B12, etc.
Copyright 2012, John Wiley & Sons Canada, Ltd.
The Vitamins
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Finding Vitamins in Foods
Copyright 2012, John Wiley & Sons Canada, Ltd.
Fortified and Enriched Foods Fortification: process of adding nutrients to
foods. The added nutrients are generally not found in the food, such as fortifying orange juice with calcium.
Enrichment: adding nutrients back to foods that have lost nutrients due to processing. An example is the addition of B vitamins to white rice.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Fortification Health Canada regulates which foods must
be fortified and which nutrients should be added.
Example: table salt with iodine milk with Vitamin D grains with thiamine, riboflavin, niacin, iron
and folic acid
Copyright 2012, John Wiley & Sons Canada, Ltd.
Dietary Supplements Dietary supplements can be another source of
vitamins in the modern diet. Dietary supplements contain some combination
of vitamins, minerals, herbs, botanicals, amino acids, enzymes or extracts.
Dietary supplements cannot replace the benefits of a diet containing a wide variety of foods.
Dietary supplements are regulated by Health Canada’s Natural Health Products Directorate.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Dietary Supplements (continued) There is a concern that natural health
products in food format may confuse the consumer.
Dietitians of Canada is concerned that the consumer may perceive these products as food, be unaware that there are maximum doses and exceed the ULs for some nutrients, with potential adverse effects, as there are no nutritional facts on these products’ labels.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Absorptionof Vitamins
Copyright 2012, John Wiley & Sons Canada, Ltd.
Bioavailability of Vitamins Vitamins must be absorbed by the body in order to
perform their functions. Approximately 40-90% of vitamins are absorbed in
the small intestine. Fat-soluble vitamins require fat in the diet to be
absorbed. Water-soluble vitamins may require transport
molecules or specific molecules in the GI tract. Some vitamins are absorbed in inactive provitamin
or vitamin precursor forms that must be converted into active forms by the body.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Thiamin Thiamin was the first B vitamin to be
identified and is also called B1. Thiamin is widely available in foods,
especially in enriched grains, whole grains, legumes, nuts and seeds.
Thiamin assists in energy production, carbohydrate metabolism, the production of ribose and the health of the nervous system.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Thiamin
Copyright 2012, John Wiley & Sons Canada, Ltd.
Riboflavin Dairy products are a good source of riboflavin. Plant sources of riboflavin include mushrooms, broccoli,
asparagus, whole grains and green, leafy vegetables. Animal sources include red meat, poultry and fish. Riboflavin is easily destroyed by heat and exposure to
light. Riboflavin is an important component in the citric acid
cycle and for assisting the body with the absorption of other vitamins.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Riboflavin
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Niacin Niacin is added to enriched flours in North America. A niacin deficiency disease is pellagra. Niacin can be synthesized in the body from the essential
amino acid tryptophan if the diet is adequate in tryptophan.
Niacin plays an important role in the production of energy and in general metabolism.
Two forms of niacin are nicotinic acid and nicotinamide.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Niacin
Copyright 2012, John Wiley & Sons Canada, Ltd.
Niacin Advanced pellagra’s symptoms include the 3
D’s: dermatitis, diarrhea and dementia. Niacin toxicity from overuse of niacin
supplements can result in elevated blood pressure, cardiac arrhythmia, nausea, vomiting, elevated blood sugar levels and impaired liver function.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Pantothenic Acid
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Vitamin B6
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Vitamin B6
Vitamin B6 is also called pyridoxine and comprises a group of compounds including pyridoxal, pyridoxine, and pyridoxamine.
All three forms can be converted into pyridoxal phosphate, which is required for many enzyme reactions in the body.
Vitamin B6 deficiency may result in anemia due to impaired hemoglobin synthesis and neurotransmitter issues.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Folate or Folic Acid
Copyright 2012, John Wiley & Sons Canada, Ltd.
Folate or Folic Acid Folate coenzymes are needed for DNA
synthesis and the metabolism of some amino acids.
Low folate intake in early pregnancy is associated with an increased risk of neural tube defects.
Low folate intake has been associated with an increased risk of heart disease related to the metabolism of the amino acid homocysteine.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Folate Deficiency and Neural Tube Defects
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Folate Fortification Neural tube defects have decreased by 50%
in Canada since food fortification. Newfoundland rates have dropped by 80%. Alberta and Quebec have found a reduction
in the number of congenital heart defects. Ontario reported a reduction in
neuroblastoma.
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Folate Fortification Some studies have shown an increase in
colon cancer since folate fortification began in 1998.
This maybe the result of folate stimulating DNA synthesis and promoting growth of pre-existing cancerous cells.
When considering food fortification it is important to consider that what may benefit one segment of the population may harm another segment.
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Macrocytic Anemia and Folate Deficiency
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Calculating Dietary Folate Amounts
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Vitamin B12
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Vitamin B12
Pernicious anemia is a form of anemia that does not respond to iron supplementation.
Vitamin B12 is necessary for the proper absorption of iron in the body.
Excessive intake of folic acid can mask B12 deficiencies.
Vitamin B12 is most readily absorbed from animal products.
Vegan diets need to be supplemented with readily-absorbable forms of B12.
Atrophic gastritis may lead to B12 deficiencies.
Copyright 2012, John Wiley & Sons Canada, Ltd.
Absorption of Vitamin B12
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Vitamin C
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Vitamin C Vitamin C is also known as ascorbic acid or
ascorbate. Vitamin C in foods can be destroyed by
oxygen, light and heat, as well as contact with copper or iron cookware.
Vitamin C functions as an antioxidant in the body, helps maintain the immune system, is important in the production of collagen and aids in iron absorption.
Copyright 2012, John Wiley & Sons Canada, Ltd.
How Antioxidants Work
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Summary of Water-Soluble Vitamins and Choline
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Summary of Water-Soluble Vitamins and Choline (continued)
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Summary of Water-Soluble Vitamins and Choline (continued)
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Benefits and Risks of Water-Soluble Vitamin Supplements
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Copyright
Copyright © 2012 John Wiley & Sons Canada, Ltd.
All rights reserved. Reproduction or translation of this work beyond that permitted by Access Copyright (The Canadian Copyright Licensing Agency) is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons Canada, Ltd. The purchaser may make back-up copies for his or her own use only and not for distribution or resale. The author and the publisher assume no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.
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Copyright 2012, John Wiley & Sons Canada, Ltd.