Chapter 8: Water-Soluble Vitamins PDF

Chapter 8: Water- Soluble Vitamins  Learning Objectives By the end of this chapter you should be able to: ✓Name the sources of vitamins in the Canadian diet. ✓Describe how bioavailability affects vitamin requirements. ✓Describe some functions of vitamins in the body. ✓For each of the vitamins disc...

Chapter 8: Water- Soluble Vitamins  Learning Objectives By the end of this chapter you should be able to: ✓Name the sources of vitamins in the Canadian diet. ✓Describe how bioavailability affects vitamin requirements. ✓Describe some functions of vitamins in the body. ✓For each of the vitamins discussed you should know: Source Functions in the body Deficiency (and therefore who might be at risk) Toxicity * You will not be expected to memorize the values for the DRIs for each. However, you should be familiar with the table in which you can locate the information (see inside cover of your textbook) so if asked you could find the information. 2 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. Deficiency symptoms occurs when a vitamin is lacking in the diet normally resolve when vitamin is restored to the diet Traditionally grouped based on solubility in water or fat allows generalizations to be made about how they are absorbed, transported, excreted, and stored in the body Water‐soluble vitamins include the B vitamins and vitamin C B vitamins were first thought to be one chemical substance but now are separately named/numbered The fat‐soluble vitamins include vitamins A, D, E, and K 3 Finding Vitamins in Foods Figure 8.1 Copyright ©2020 John Wiley & Sons, Inc. 4 Fortified Foods Fortification – describes the process of adding nutrients to foods such as the addition of vitamin D to milk Adding nutrients to food is an effective way to supplement nutrients that are deficient in the population’s diet without having to rely on consumers to alter their food choices or to take nutrient supplements Levels of nutrients added are based on an amount that is high enough to benefit those who need to increase their intake but not so high as to increase the risk of excessive intakes in others 5 Fortified Foods Enrichment – a food that has had nutrients added to restore those lost in processing to a level equal to or higher than originally present. Which foods are enriched or fortified, which nutrients are added, and how much of a nutrient is added depends on the food supply, the needs of the population, and public health policies Mandatory: fortification of table salt with iodine fortification of milk with vitamin D, and the enrichment of grains with thiamin, riboflavin, niacin, and iron fortification of grains with folic acid help to prevent micronutrient deficiencies 6  Considering Supplements While a healthy dietary pattern is the best choice for most of the population, there are groups for whom supplements are an appropriate and useful addition to the regular diet. These include: Dieters – calorie‐restricted diets may benefit from a supplement (risk of developing deficiencies) Vegans and those who eliminate all dairy foods – May supplement to obtain adequate vitamin B12 (no animal products need to supplements or consume B12‐fortified foods. Also without dairy (e.g. intolerance or allergies) for calcium and vitamin D Infants and children – Supplemental fluoride, vitamin D, and iron are sometimes recommended Young women and pregnant women – consume 400 µg of folic acid daily from supplements. Pregnant women - Supplements of iron, folic acid, multivitamin and mineral supplements Older adults – Because of the high incidence of atrophic gastritis in adults over 50, vitamin B12 supplements or fortified foods are recommended. Meeting RDA for vitamin D may be difficult for older adults so supplements are recommended. Individuals with dark pigmentation or who cover their bodies when outdoors – Those with dark skin or who fully cover their bodies when outdoors may not be able to synthesize enough vitamin D and may therefore benefit from supplementation. Individuals with restricted diets – health conditions that affect what foods they can eat or how nutrients are used (or absorbed) may require vitamin and mineral supplements. People taking medications – Medications may interfere with the body’s use of certain nutrients. Cigarette smokers and alcohol users – Heavy cigarette smokers require more vitamin C than non‐smokers. Alcohol consumption inhibits the absorption of B vitamins and may interfere with 7 metabolism. Vitamins in the Digestive Tract Figure 8.4 Copyright ©2020 John Wiley & Sons, Inc. 8 Vitamins in the Digestive Tract Bioavailability – A general term that refers to how well a nutrient can be absorbed and used by the body Key factor for bioavailability –> vitamin is soluble in fat or water Fat‐soluble vitamins require fat for absorption (poorly absorbed when the diet is very low in fat) Water‐soluble vitamins many depend on energy‐requiring transport systems or must be bound to specific molecules in GI tract to be absorbed e.g. thiamin and vitamin C are absorbed by energy‐requiring transport systems e.g. riboflavin and niacin require carrier proteins for absorption e.g. vitamin B12 must be bound to a protein produced in the stomach before it can be absorbed 9 Vitamins in the Digestive Tract Once absorbed into the blood, vitamins must be transported to the cells Most water‐soluble vitamins are bound to blood proteins for transport Fat‐soluble vitamins are incorporated into lipoproteins or bound to transport proteins to be transported o vitamins A, D, E, and K incorporated into chylomicrons Some vitamins are absorbed in inactive provitamin or vitamin precursor forms that must be converted into active vitamin forms once inside the body How much of each provitamin can be converted into the active vitamin and the rate at which this occurs affect the amount of a vitamin available to function in the body 10 Storage and Excretion The ability to store and excrete vitamins helps to regulate the amount present in the body water‐soluble vitamins are easily excreted from the body in the urine (except B12) are rapidly depleted because they are not stored significantly and they must be consumed regularly in the diet takes more than a few days to develop deficiency symptoms, even when completely absent from the diet Fat‐soluble vitamin are stored in the liver and fatty tissues and cannot be excreted in the urine because they are stored to greater extent, takes longer to develop a deficiency of fat‐soluble vitamins when not provided by the diet 11 Vitamin Recommended Intakes Recommendations for vitamin intake for healthy populations in the United States and Canada are made by the Dietary Reference Intakes (DRIs) DRIs provide either a RDA value (when sufficient information is available to establish an EAR), or an AI (when a recommendation is estimated from population data) Values are used as a goal for dietary intake by individuals DRIs also establish ULs as a guide to the maximum amount of a nutrient that is unlikely to cause adverse health effects Meeting needs without exceeding a safe level of intake requires careful attention to foods chosen, knowledge of the nutrients added to foods and those consumed in supplements 12  Understanding Vitamins Functions Coenzymes – Small nonprotein organic molecules that act as carriers of electrons or atoms in metabolic reactions and are necessary for the proper functioning of many enzymes Figure 8.5 13 Vitamins Function Together B Vitamins and Energy Metabolism Figure 8.6 14 Vitamins Function Together Vitamin B6, Folate, and B12 Function Together Vitamin B6, folate, and vitamin B12 function together in metabolic pathways related to single carbon metabolism Pathways support fetal development, the formation of red blood cells, and the health of nerve tissue Common combination in pre-natal vitamins Vitamin C and Vitamin E Function Together Vitamin C is a coenzyme that is essential for the synthesis of neurotransmitters, hormones, and collagen, a protein vital to the structure of connective tissue Works with vitamin E to protect the body from oxidative damage 15 Summary – Water-Soluble Vitamins 16  Thiamin Sources of Thiamin (B1) Large proportion of thiamin consumed comes from enriched products Mandatory addition to white flour and pastas (labelled as enriched), infant formula, simulated meats, simulated egg products, instant breakfasts, and meal replacement products Voluntary addition to products like breakfast and infant cereals Pork, whole grains, legumes, nuts, seeds, and organ meats (liver, kidney, heart) are also good sources Thiamin in foods may be destroyed during cooking or storage (sensitive to heat, oxygen, and low‐acid conditions) Thiamin bioavailability is affected by anti‐thiamin factors that destroy it anti-thiamin factors may be inactivated by cooking Other anti‐thiamin factors not inactivated by cooking are found in tea, coffee, betel nuts, blueberries, and red cabbage 17 Thiamin Functions Important in the energy‐yielding reactions in the body – essential to the production of ATP from glucose Active form, thiamin pyrophosphate, is a coenzyme for reactions in which carbon dioxide is lost from larger molecules e.g. reaction that forms acetyl‐CoA from pyruvate and one of the reactions of the citric acid cycle require thiamin pyrophosphate Needed for the metabolism of other sugars and certain amino acids; the synthesis of the neurotransmitter acetylcholine; and the production of the sugar ribose (needed to synthesize RNA) RDA is based on 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 increased to accommodate increased growth and energy utilization18 Thiamin Deficiency Results in the disease beriberi –> causes lethargy, fatigue, and other neurological symptoms Can also cause cardiovascular problems such as rapid heartbeat, enlargement of the heart, and congestive heart failure Beriberi is rare in NA – thiamin deficiency does occur in alcoholics vulnerable because thiamin absorption is decreased due to the effect of alcohol on the GI tract liver damage occurs with chronic alcohol consumption reduces activation Thiamin‐deficient alcoholics may develop a neurological condition Toxicity None reported so UL for thiamin intake has not been established 19 Thiamin Figure 8.8 Copyright ©2020 John Wiley & Sons, Inc. 20  Riboflavin Sources of Riboflavin (B2) Milk is the best source of riboflavin in the Canadian diet. Mandatory addition to white flour and pastas (labelled as enriched), infant formula, simulated meats, simulated egg products, instant breakfasts, and meal replacement products Voluntary addition to a number of other products, such as breakfast and infant cereals Liver, red meat, poultry, fish, and whole and enriched grain products are also good sources Vegetable sources include asparagus, broccoli, mushrooms, and leafy green vegetables such as spinach Riboflavin is destroyed by exposure to light –> poor handling decreases riboflavin content Cloudy plastic milk bottles block some light, but cardboard or opaque plastic milk containers are even better at preventing losses 21  Riboflavin Functions Riboflavin forms the active coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) FAD functions in the citric acid cycle and is important for the breakdown of fatty acids FMN and FAD function as electron carriers in the ETC Adequate riboflavin is crucial in providing energy from carbohydrate, fat, and protein Riboflavin is also involved directly or indirectly in converting other vitamins (folate, niacin, vitamin B6, and vitamin K) into active forms RDA is based on amount of riboflavin needed to maintain normal activity of a riboflavin‐dependent enzyme in red blood cells and normal riboflavin excretion in the urine increased to accommodate increased growth and energy utilization 22 Riboflavin Deficiency Not common on its own and often seen in conjunction with deficiencies in other B vitamins Results in the disease ariboflavinosis –> symptoms include inflammation of the eyes, lips, mouth, and tongue; scaly, greasy skin eruptions; cracking of the tissue at the corners of the mouth; and confusion Causes injuries heal poorly because new cells cannot grow to replace the damaged ones. Tissues that grow most rapidly, such as the skin and the linings of the eyes, mouth, and tongue, are the first to be affected Toxicity None reported so UL for thiamin intake has not been established 23 Riboflavin Figure 8.10 Copyright ©2020 John Wiley & Sons, Inc. 24