Chapter Review

BRING IT HOME

CHAPTER 10 BRING IT HOME

Focus on the fat-soluble vitamins

On any given day, you can explore scientific literature or read headlines in the news and find articles reporting the results of research on vitamins and their role in promoting health or preventing disease. To acquaint yourself with some of the newer research and vitamin news, choose one of the fat-soluble vitamins and explore media outlets and the scientific literature for recent reports and studies.

  1. Using a popular search engine (for example: Google News), search for recent media articles or reports (in newspapers, on television, or from other popular news providers) that highlight either vitamin A, E, D, or K. List one to two recent headlines and their sources that feature any report, finding, or claim regarding the vitamin you have chosen. (For example: “Vitamin D found to reduce risk of asthma” USA Today.)

  2. Visit the MEDLINE database at www.pubmed.gov (which is maintained by the U.S. National Library of Medicine at the National Institutes of Health) for access to thousands of abstracts from peer-reviewed medical and scientific journal abstracts. Type your vitamin’s name in the search box. Scroll through the first page or two listing of articles, taking note of the variety and focus of research. If you are looking for information on a specific claim, you might search the vitamin and the condition; for example, “vitamin D AND asthma.” List the title and source of at least two abstracts.

  3. You can access an abstract or summary of the research in PubMed by clicking on the link of the article. Skim the one to two abstracts you listed, taking note of the author’s results or conclusions. Briefly describe the study findings on the vitamin.

  4. Research on diet, including the risks and benefits of vitamins, is abundant and ongoing. Briefly discuss new research areas or findings about the vitamin you explored.

  5. Imagine yourself a nutrition scientist. What research questions might you propose on the vitamin you’ve explored?

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KEY IDEAS

KEY IDEAS

  • Vitamins are organic compounds (containing both carbon-carbon and carbon-hydrogen bonds) that are needed in small quantities for very specific functions, such as the maintenance of regulatory and metabolic processes in the body.

  • Most vitamins are in their active form (preformed) in foods, however, in some cases, inactive, precursor forms of vitamins, called provitamins, must be converted to fulfill biological functions in the body.

  • Inadequate or excessive intake of vitamins can lead to deficiency or toxicity with adverse health effects.

  • The 14 known vitamins are classified by their solubility as fat-soluble or water-soluble.

  • The fat-soluble vitamins—A, D, E, and K—have diverse functions in the body.

  • Fat-soluble vitamins are transported in the body via the lymph and excess intake is stored in fatty tissues and the liver, from which they are released when needed.

  • The body derives vitamin A from preformed A (retinol) found in animal foods and fortified foods. And, to a lesser degree, from provitamin A carotenoids in plant foods, as conversion to the active form is incomplete.

  • Vitamin A serves many critical biochemical and physiological functions in the body related to vision, cell development, reproduction, immune function, and growth, among others. The carotenoids have antioxidant properties in the body, which help protect cells from damage caused by free radicals.

  • Vitamin D, which functions as a hormone in the body, is actually not considered an essential nutrient in the diet because it can be synthesized from cholesterol through exposure of the skin to UV light. Among other important functions, vitamin D plays a key role in the growth and maintenance of bone in part through its role in maintaining calcium concentrations in the blood.

  • Serving primarily as an antioxidant in the body, vitamin E encompasses a group of fat-soluble compounds called tocopherols found primarily in nuts and vegetable oils. Only alpha-tocopherol meets dietary requirements in humans.

  • Vitamin K is an essential nutrient found in foods such as leafy greens. A significant amount of our daily requirement may also be produced by bacteria in the intestine.

  • Vitamin K plays a key role in blood clotting and in bone metabolism.

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NEED TO KNOW

NEED TO KNOW

Review Questions

Question 10.11

1. Characteristics of vitamins include all of the following, EXCEPT they:

  1. are considered micronutrients.

  2. do not provide energy.

  3. contain carbon molecules.

  4. are incorporated into the structure of cells.

  5. are necessary for development and growth.

1. d

Question 10.12

2. Vitamins are classified according to their:

  1. bioavailability.

  2. function.

  3. molecular structure.

  4. solubility.

2. d

Question 10.13

3. Inactive, precursor forms of vitamins are termed:

  1. antioxidants.

  2. enzymes.

  3. hormones.

  4. preformed vitamins.

  5. provitamins.

3. e

Question 10.14

4. Possible toxicity from vitamins is MOST likely to occur with consuming:

  1. large portions of vegetables and fruits.

  2. excess intake of water-soluble vitamins.

  3. fortified foods and dietary supplements.

  4. more than two servings of milk per day.

4. c

Question 10.15

5. All of the following are TRUE regarding carotenoids, EXCEPT:

  1. only three are converted to active vitamin A, with beta-carotene as the most abundant.

  2. they are primarily provitamins that must be converted before they can be utilized in the body.

  3. they are the yellow, orange, and red pigments in fruits and vegetables.

  4. they supply approximately two-thirds of vitamin A in the U.S. diet.

  5. they function as antioxidants in reducing damage from free radicals.

5. d

Question 10.16

6. Vitamin A deficiency:

  1. compromises the ability to see in low light.

  2. results in keratinization of epithelial cells.

  3. increases the risk of death from infectious disease in children.

  4. is the leading cause of preventable blindness in children worldwide.

  5. All of the answers are correct.

6. e

Question 10.17

7. All of the following are TRUE regarding vitamin D, EXCEPT:

  1. it is also known as cholecalciferol.

  2. its synthesis in the body is not diminished by use of sunscreens.

  3. it is important for maintaining calcium concentrations in the blood.

  4. it is only essential in the diet when sun exposure or synthesis is insufficient to meet needs.

  5. it functions as a hormone in the body.

7. b

Question 10.18

8. The Recommended Dietary Allowances (RDA) for vitamin D:

  1. are established based on minimal sun exposure.

  2. are established based on maximum sun exposure of 4 to 6 hours a day.

  3. are established to maintain calcium concentrations in healthy people.

  4. can be met through the consumption of adequate amounts of fruits and vegetables.

  5. can only be met through the use of dietary supplements.

8. a

Question 10.19

9. The fat-soluble vitamin that is LEAST likely to be toxic when consumed in amounts above recommended intake levels is:

  1. vitamin A.

  2. vitamin D.

  3. vitamin E.

  4. All of the fat-soluble vitamins have some risk of toxicity.

9. c

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Question 10.20

10. All of the following are characteristics of vitamin E as an antioxidant, EXCEPT that it:

  1. protects against the oxidation of poly-unsaturated fatty acids in cell membranes.

  2. boosts the functioning of the immune system by protecting white blood cells.

  3. protects against oxidative damage that results from exposure to free radicals.

  4. protects the fat in low-density lipoproteins from oxidation.

  5. dramatically reduces the risks of heart disease and cancer.

10. e

Question 10.21

11. Vitamin K has a key role in:

  1. blood clotting.

  2. energy metabolism.

  3. the formation of red blood cells.

  4. nerve impulse transmission.

  5. regulating blood glucose.

11. a

Question 10.22

12. Which of the following is the BEST food source of vitamin K?

  1. apples

  2. Brussels sprouts

  3. eggs

  4. lean beef

  5. yogurt

12. b

Dietary Analysis Using SuperTracker

Dietary Analysis Using SuperTracker

Analyzing the intake of fat-soluble vitamins using SuperTracker

Question 10.23

1. Log onto the United States Department of Agriculture (USDA) website at www.supertracker.usda.gov. If you have not done so already, you will need to create a profile to get a personalized diet plan. This profile will allow you to save your information and diet intake for future reference. Do not use the general plan.

Question 10.24

2. Click the Track Food and Activity option.

Question 10.25

3. Record your food and beverage intake for one day that most reflects your typical eating patterns. Enter each food and beverage you consumed into the food tracker. Note that there may not always be an exact match to the food or beverage that you consumed, so select the best match available.

Question 10.26

4. Once you have entered all of your food and beverage choices into the food tracker, on the right side of the page under the bar graph, you will see Related Links: View by Meal and Nutrient Intake Report. Print these reports and use them to answer the following questions:

  1. Did you meet the target recommendations for the fat-soluble vitamins (A, D, E, and K) on the day you selected? If not, which vitamins fall below the target numbers?

  2. For each vitamin target that you missed, list two specific foods you could consume to increase your intake of that vitamin. For vitamins for which you met the target, what foods contributed most to your intake?

  3. Were you above the targets for any of the fat-soluble vitamins? If so, which ones? Are any of these numbers above the toxicity level for that vitamin?

  4. Fat-soluble vitamins require dietary fat to be optimally absorbed. If you ate a tossed salad, what could you include in the salad to help you absorb the fat-soluble vitamins?