Chapter 10: Fat-Soluble Vitamins
Dietary cholecalciferol must be further hydroxylated in order to be active vitamin D. The first hydroxylation occurs in the _____ to produce _____. a. liver, 25-hydroxycholecalciferol b. kidney, 25-hydroxycholecalciferol c. skin, 7-dehydrocholesterol d. kidney, 1-hydrocholesterol
a. liver, 25-hydroxycholecalciferol Vitamin D reaching the liver either by way of chylomicron remnants or by DBP must be hydroxylated by cytochrome P-450 hydroxylases to begin the generation of vitamin D's active form. In the liver, 25-hydroxylase (primarily CYP2R1), which is NADPH-dependent, functions in the mitochondria to hydroxylate vitamin D at carbon 25 to form 25-OH (vitamin) D, also called calcidiol or 25-OH cholecalciferol. While the liver expresses most of the 25-hydroxylases, the enzyme is found in other organs, including the lungs, intestine, and kidneys.
Which is NOT related to the functions of vitamin A? a. neurological function b. growth c. immunity d. cell differentiation
a. neurological function
Risk of vitamin K deficiency is greatest in: a. newborns. b. children. c. adolescents. d. older people.
a. newborns. A deficiency of vitamin K is unlikely in healthy adults. The population groups that appear to be most at risk for a vitamin K deficiency are newborn infants, people being treated chronically with antibiotics, people with severe gastrointestinal malabsorptive disorders, and the elderly. Newborns are particularly at risk because their food is limited to milk, which is low in vitamin K; their stores of the vitamin are low because inadequate amounts cross the placenta; and their intestinal tract is not yet populated by vitamin K-synthesizing bacteria.
Immediately following a balanced meal that contained vitamin E (such as fortified milk), where would you most likely find most of the vitamin E in the body? a. in the portal blood as α-tocopherol b. in the general circulation bound to RBC c. inside cells as free α-tocopherol d. stored in adipose tissue e. in chylomicrons in the lymphatic vessels and general circulation
e. in chylomicrons in the lymphatic vessels and general circulation In the enterocyte, absorbed tocopherols are incorpo- rated into chylomicrons for transport through the lymph and then into circulation.
Vitamers: Match each vitamer with its function. 1. 11-cis retinal 2. retinoic acid 3. alpha-tocopherol 4. calcitriol 5. hydroquinone (KH2) a. interacts with nuclear VDR to increase calbindin b. required for carboxylation of glutamic acid c. needed for binding with opsin in the photoreceptor rod cells d. transported into nucleus to affect gene transcription of keratin proteins e.donates hydrogens to terminate propagation of membrane lipid peroxidation chain reactions
1. C 2. B 3. E 4. A 5. D
True or False: 7-dehydrocholesterol is the form of vitamin D that is added to fortify milk.
False Explanation: Cholecalciferol is the form added to fortify milk.
True or False: All of the functions of vitamin A are carried out by retinoic acid via transcriptional mechanisms.
False Explanation: E.g., retinal for the visual cycle.
True or False: All three forms of vitamin A (retinol, retinal, retinoic acid) are stored in the liver as retinyl esters.
False Explanation: Only retinol is stored in the liver, as retinyl esters.
True or False: Because β-carotene can be converted into retinol, plant sources are referred to as preformed vitamin A.
False Explanation: Plant sources are provitamin A.
True or False: Gut bacteria can produce some vitamins, but this rarely contributes to our requirements because they are not absorbed.
False Explanation: Vitamin K, folate, biotin—all contribute to the requirement.
True or False: Calcium homeostasis in the blood depends on intestinal absorption, bone resorption, and kidney reabsorption.
True
True or False: D increases the abundance of calbindin (Ca++ transporter) in enterocytes by increasing the transcription of the calbindin gene.
True
Which vitamin is said to be essential for growth and immune system function? a. K b. A c. D d. E
b. A
Which vitamin directs cellular differentiation of epithelial cells? a. riboflavin b. vitamin K c. vitamin E d. vitamin A
d. vitamin A
Vitamin A functions in the visual cycle. This mechanism involves a vitamin A molecule called ___A____, combining with ___B___ to form ___C___. When photon energy strikes this molecule, it splits and causes a conformational change in the molecule, causing an electrical signal to be sent to the brain. Blank A, B, & C: a. rhodopsin b. 11-cis retinal c. all-trans retinal d. retinol e. opsin f. retinoic acid
1. B 2. E 3. A In the case of vision, it is the 11-cis retinal form that must bind to the protein opsin of visual pigments to mediate photo- transduction (the process by which light is converted into electrical signals for the brain). Vitamin A is needed to form rhodopsin (a vitamin A-containing pigment protein) found in the rods. Rhodopsin is made up of vitamin A as 11-cis retinal and the protein opsin.
True or False: A good source of vitamin D is milk, because it is fortified with 1,25-(OH)2-vitamin D3.
False Explanation: Fortified with vitamin D3 (cholecalciferol)—not hydroxylated at either carbon 25 or carbon 1.
True or False: Many anticoagulants inhibit the vitamin K cycle, thereby preventing activation of clotting proteins.
True
True or False: Many anticoagulants work by inhibiting the regeneration of active vitamin K (i.e., dihydrovitamin KH2) during the vitamin K cycle.
True
True or False: Production of active vitamin D requires skin, sunlight, cholesterol, the liver, and the kidneys.
True
True or False: Rhodopsin is simply the opsin protein after it has been activated by 11-cis-retinal.
True
Which of the following is needed for the visual cycle? a. 11-cis retinal b. 9-cis retinoic acid c. lycopene d. cryptoxanthin
a. 11-cis retinal In the case of vision, it is the 11-cis retinal form that must bind to the protein opsin of visual pigments to mediate phototransduction (the process by which light is converted into electrical signals for the brain). Vitamin A is needed to form rhodopsin (a vitamin A-containing pigment protein) found in the rods. Rhodopsin is made up of vitamin A as 11-cis retinal and the protein opsin
Who discovered vitamin E? a. Evans and Bishop b. McCollum and Davis c. Mellanby and Hopkins d. Simon and Garfunkel
a. Evans and Bishop The term tocopherol is derived from the Greek word tokos, which means "childbirth," and phero, which means "to bear or bring forth." This terminology is based upon the vitamin's discovery by H. Evans and K. Bishop in the early 1920s, when they found that rats could not reproduce when given a diet of rancid lard.
Why is retinoic acid considered a hormone? a. It has receptors on the nucleus and causes a change in protein synthesis. b. It has a biologic function similar to insulin. c. It is synthesized in the same tissue that it affects. d. It causes the catabolism (break down) of body proteins.
a. It has receptors on the nucleus and causes a change in protein synthesis.
In what type of tissue is the largest amount of vitamin E stored? a. adipose b. heart c. lung d. brain
a. adipose There is no single storage organ for vitamin E. The largest amount (over 90%) of the vitamin is concentrated in an unesterified form in fat droplets in adipose tissue. The concentration of vitamin E in adipose tissue increases linearly with the dosage of vitamin E; however, release of vitamin E from adipose tissue is slow even during periods of low vitamin E intake.
Which tocopherol form provides the most vitamin E activity in the U.S. food supply? a. alpha b. beta c. gamma d. delta
a. alpha Vitamers in both classes are designated as α, β, γ, or δ. Only α-tocopherol has biologic activity and can meet the body's need (requirement) for the vitamin. Moreover, the body cannot interconvert the vitamers.
How will retinol, once secreted from the liver, be found in the blood? a. attached to RBP and transthyretin b. attached to albumin c. attached to a chylomicron d. attached to RBP and stellate cells
a. attached to RBP and transthyretin Retinol transport in the blood requires two specific proteins, retinol-binding protein (RBP) and transthyretin, also known as prealbumin and as thyroxine-binding globulin.
What form of vitamin D is the major circulating form with a half-life of approximately 3 weeks? a. calcidiol b. calcitriol c. cholecalciferol d. vitamin D2
a. calcidiol Calcidol is the major circulating metabolite of cholecalciferol, while calcitriol is the hormone that upregulates the active transport of calcium from the gut, and which suppresses parathyroid hormone secretion. At a typical daily intake of vitamin D3, its full conversion to calcifediol takes approximately 7 days. Calcifediol is then converted in the kidneys (by the enzyme 25(OH)D-1α-hydroxylase) into calcitriol (1,25-(OH)2D3), a secosteroid hormone that is the active form of vitamin D. Because little 25-OH D remains in the liver and very little is taken up by the extrahepatic tissues, the blood is the largest single pool (and represents the major storage site) of 25-OH D, which has a half-life of about 15 days to 3 weeks or more.
Free radicals take electrons from all of the following EXCEPT _____. a. calcitriol b. DNA c. proteins d. PUFAs
a. calcitriol Once formed, free radicals attack, taking electrons from cell constituents (including nucleic acid in DNA in the nucleus of cells). They also take electrons from proteins (especially amino acids such as tyrosine, tryptophan, proline, histidine, or arginine and those with sulfhydryl groups, such as cysteine) and polyunsaturated fatty acids in cell membranes or in the membranes of intracellular organelles, such as the nucleus, mitochondria, or endoplasmic reticulum.
In assessing the vitamin D status of an individual, which measure would you use? a. circulating 25-OH cholecalciferol b. circulating 1,25-OH2 cholecalciferol c. circulating cholecalciferol d. serum calcium levels
a. circulating 25-OH cholecalciferol. Serum 25-OH D concentrations are most often used to assess vitamin D status. Concentrations less than 25 to 30 nmol/L (10-12 ng/mL) have typically been diagnostic of a vitamin D deficiency; however, newer research suggests serum 25-OH D concentrations less than 50 nmol/L (20 ng/mL) represent deficiency, and concentrations in the range of 50 to 72 nmol/L (20-29 ng/mL) constitute vita- min D insufficiency. Serum 25-OH D concentrations in excess of about 75 or 80 to 100 nmol/L (30 or 32-40 ng/ mL) are thought to be needed for bone health
Sun exposure does not cause hypervitaminosis D because _____. a. cutaneous production of the vitamin reaches a maximum b. sunburned skin is not sensitive to the UV wavelength that causes previtamin D3 synthesis c. inactive products are synthesized from pre-vitamin D3 and D3 d. vitamin D-binding protein is not saturated with D3
a. cutaneous production of the vitamin reaches a maximum Cutaneous production of the vitamin reaches a maximum of about 20,000 IU, and extensive whole-body irradiation with ultraviolet light generally raises serum 25-OH D concentrations to about 100 to 200 nmol/L (40-80 ng/mL); levels greater than about 500 nmol/L (200 ng/mL) are associated with toxicity.
In order to be carried in the chylomicron, retinol (once in the enterocyte) is _____. a. esterified by lecithin retinol acyl transferase b. converted to retinaldehyde by retinaldehyde reductase c. attached to a VLDL d. attached to an RXR receptor on the nucleus
a. esterified by lecithin retinol acyl transferase
29. An individual with poor vitamin A status would have a _____ RDR than someone with a good vitamin A status. a. greater b. lesser
a. greater Adequacy of vitamin A stores in the liver can be assessed by the relative dose response (RDR) test or the modified relative dose response (MRDR) test. The RDR test involves measuring changes in plasma retinol concentration before and 5 hours after oral administration of retinyl esters (usually as acetate or palmitate). A % RDR equal to or greater than 20% suggests inadequate liver vitamin A stores.
The RDA for vitamin D for people over the age of 70 is _____ the RDA for teenagers. a. greater than b. less than c. equal to
a. greater than The recommendations, which assume minimal sun exposure, suggest an intake of 600 IU (15 μg) of vita- min D for children (age 1 year and older), adolescents, and adults including women who are pregnant or lactating. Recommended intakes increase to 800 IU (20 μg) of vitamin D for adults older than 70 years of age.
What is a symptom of a vitamin D toxicity? a. hypercalcemia b. hypocalcemia c. rickets d. osteoporosis
a. hypercalcemia Manifestations of toxicity include hypercalcemia and calcinosis, the associated calcification of soft tissues including organs such as the kidneys, heart, and lungs, along with blood vessels.
Anticoagulant drugs that act by inhibiting vitamin K activity do so by which mechanism? a. inhibiting the formation of the active form of vitamin K b. interfering with micelle formation so vitamin K is not absorbed c. not allowing calcium to interact with Gla residues d. stimulating osteocalcin synthesis
a. inhibiting the formation of the active form of vitamin K. Anticoagulants such as warfarin antagonize the synthesis of vitamin K by interfering with the activity of epoxide reductase. Ingestion of diets high in vitamin K, as obtained from about a pound of broccoli daily, override the effects of warfarin. Thus, people who are taking anticoagulant medications are instructed to maintain a consistent intake of vitamin K, but also to avoid consumption of large quantities of foods rich (about 700-1,500 μg or more of phylloquinone) in vitamin K at a single meal.
What happens to retinal in the enterocyte? a. it is esterified b. it is reduced to retinol c. it is transported into the portal blood d. 15, 15' dioxygenase acts to form beta-carotene
a. it is esterified Within enterocytes, retinoids also undergo metabo- lism. Retinal, produced from β-carotene or other carotenoids, is reduced by retinal/retinaldehyde reductase, an NADH-dependent enzyme, to retinol. Additionally, the vitamin must be reesterified to enable its incorporation into chylomicrons for release into the blood. Retinol, whether formed by carotenoid oxidation or originating from dietary retinyl esters, follows one of two metabolic pathways for reesterification within the enterocyte.
Within the nucleus, all trans-retinoic acid and/or 9-cis retinoic acid binds to _____. a. nuclear retinoic acid receptors b. mannosylated glycoproteins c. cell aggregates d. transcription factors
a. nuclear retinoic acid receptors Two forms of vitamin A, all-trans retinoic acid and 9-cis retinoic acid (generated from retinol), regulate gene expression (Figure 10.9). Retinoic acid is thought to be transported into the nucleus by two intracellular lipid-binding proteins (iLBPs) found in the cell cytosol; these proteins in turn direct retinoic acid by binding to different nuclear receptors. Cellular retinoic acid-binding protein (CRABP) II, one iLBP, carries the vitamin to nuclear retinoic acid receptors, while another iLBP called fatty acid-binding protein 5 transports the vitamin to nuclear peroxisome proliferator-activated re- ceptors (PPAR) β/δ.
In what cells will you find most of the retinol and vitamin A stored? a. stellate b. gallbladder c. fundus d. antrum
a. stellate Retinol that has been esterified may be stored in the liver. Some storage of retinol occurs in the parenchymal cells, but about 80% to 95% of the retinol is stored in the liver in small perisinusoidal cells called stellate cells (also known as Ito cells), which constitute less than 15% of total liver cells.
Induction of a protein (i.e., increasing the amount of a protein) via increasing gene expression can be accomplished by: a. vitamin A. b. folate. c. vitamin C. d. more than one of these vitamins
a. vitamin A.
Which antioxidant is most effective in terminating chain-propagation reactions in cell membranes? a. vitamin E b. vitamin C c. vitamin K d. beta-carotene
a. vitamin E Vitamin E, being lipid soluble and located near or in membranes, effectively reacts with many radicals, especially carbon-centered radicals and those that initiate peroxidation, such as peroxyl radicals. Specifically, vitamin E donates its phenolic hydrogen on the carbon 6 hydroxyl group. Vitamin E's chromanol ring then stabilizes the unpaired electron.
Which is retinyl palmitate? a. A b. B c. C d. D e. E
b. B
Which vitamin has as its primary function the maintenance of calcium homeostasis? a. A b. D c. E d. K
b. D Calcitriol synthesis is stimulated in response to changes in serum calcium concentrations and the release of PTH. Hypocalcemia (low serum calcium concentrations, i.e., <8.5 mg/dL) initially stimulates the secretion of PTH from the para- thyroid gland through activation of calcium-sensing receptors.
A deficiency of which vitamin is commonly associated with rickets? a. A b. D c. E d. K
b. D In infants and children, vitamin D deficiency causes rickets, a condition characterized by seizures as well as growth retardation and failure of bone to mineralize. In vitamin D-deficient infants, the epiphyseal cartilage continues to grow and enlarge without replacement by bone matrix and minerals. These effects are especially visible at the wrists, ankles, and knees, all of which enlarge. In addition, long bones of the legs bow and knees knock as weight-bearing activity such as walking begins. The spine becomes curved, and pelvic and thoracic deformities—such as rachitic rosary, characterized by costochondral beading at the juncture of the ribs and cartilages—occur.
Which of the carotenoid pigments has the greatest vitamin A activity? a. alpha-carotene b. beta-carotene c. gamma-carotene d. delta-carotene
b. beta-carotene Carotenoids are synthesized by a wide variety of plants and thus are found naturally in many fruits and vegetables. One of the most abundant carotenoids is β-carotene, which exhibits the greatest amount of provitamin A activity.
The current thought about using antioxidant supplements to decrease risk to cancer and heart disease is: a. more is better. b. eat antioxidant-rich foods instead. c. vitamin E supplements work; β-carotene does not. d. only vitamin C has much promise.
b. eat antioxidant-rich foods instead. Despite the promising results of many in vitro studies, the results of supplementation trials in vivo to prevent or treat disease are not consistent, and sometimes have shown that vitamin supplementation may be detrimental to health. However, enjoying a diet rich in fruits, vegetables, and whole grains is always encouraged to help prevent disease and maintain health.
The action of vitamin K is the post-translational synthesis of blood clotting factors occurs: a. in the blood. b. in the liver. c. in the small intestine. d. in the bone marrow.
b. in the liver.
Mr. S. takes warfarin due to his valve replacement surgery. He is an avid gardener and enjoys eating the many green leafy vegetables he grows. You caution Mr. S. to tell his physician about this because the amount of warfarin he takes may need to be _____ a. decreased b. increased
b. increased
Choose the food that is high in vitamin A palmitate. a. spinach b. liver c. carrots d. pumpkin
b. liver Vitamin A is found primarily in selected foods of animal origin, especially liver; dairy products (including milk, cheese, and butter); eggs; fish, such as tuna (55 IU or 16.5 μg/3 oz), sardines (92 IU or 27.6 μg/3 oz), and herring (731 IU or 220 μg/3 oz); and fish oils, such as cod liver oil. Liver (3 oz beef) provides about 22,000 IU (6,600 μg) of vitamin A. An egg contains about 280 IU (84 μg) of vitamin A. Milk has about 500 IU (150 μg) of vitamin A/cup and cheddar and Swiss cheeses (1 oz) contain about 285 IU (85 μg) and 200 IU (60 μg) of vitamin A.
How does alpha-tocopherol differ from beta-tocopherol? a. saturation of side chain b. location of methyl groups c. source in the diet
b. location of methyl groups All tocopherols and tocotrienols found naturally in foods have an RRR stereochemistry. R and S are used to designate stereoisomers of asymmetrical molecules such as vitamin E. The most biologically active form is RRR α-tocopherol, which was once called d-α-tocopherol.
Where would you find retinoid X receptors (RXR)? a. cytosol b. nucleus c. mitochondria d. none of the above
b. nucleus
Which is the best measure of vitamin K status? a. des-γ-carboxyglutamic prothrombin b. prothrombin time c. INR d. PTH concentration
b. prothrombin time Prothrombin time, which measures the time required for a fibrin clot to form following the addition of calcium and other substances to citrated plasma, is normally between about 11 and 14 seconds; times greater than 25 seconds are associated with major bleeding and may indicate possible vitamin K deficiency. This test, however, is relatively insensitive because plasma prothrombin concentrations must usually decrease considerably (sometimes 50% or more) before any effects on prothrombin time are observed.
Which is the best technique to assess status of vitamin A liver stores? a. serum retinol levels b. the relative dose response c. clinical eye examinations
b. the relative dose response
Which antioxidant is most effective in rapidly eliminating hydroxyl radicals prior to initiation of oxidative damage? a. vitamin E b. vitamin C c. vitamin K d. beta-carotene
b. vitamin C Vitamin C and other water-soluble compounds, such as uric acid, thiols including glutathione and dihydrolipoic acid, and possibly other substances such as metallothionein, serve to defend against hydroxyl radicals. Vitamin E, in contrast, is less effective in eliminating hydroxyl radicals.
Which fat-soluble vitamin has as its principal function the maintenance of membrane integrity? a. vitamin D b. vitamin E c. vitamin A d. vitamin K
b. vitamin E The hydrogen ions from α-tocopherol effectively and quickly react with and terminate a variety of free radicals before the free radicals can destroy cell membranes and other cell components.
Which micromineral deficiency interferes with vitamin A metabolism by reducing retinol-binding protein? a. manganese b. zinc c. selenium d. iron
b. zinc Protein and zinc influence vitamin A status and trans- port. Second, overall vitamin A metabolism is closely related to protein and zinc status because the transport and use of the vitamin depend on two vitamin A-binding proteins and because zinc is required for protein synthesis as well as for alcohol dehydrogenase activity, which converts retinol to retinal. Impairments in the synthesis of retinol-binding protein and transthyretin have been shown to diminish retinol mobilization from the liver.
Choose the phrase which best explains the following statement: "β-carotene is no magic bullet." a. β-carotene does not decrease the reactivity of singlet oxygen molecules. b. β-carotene is not the only health-promoting molecule in fruits and vegetables. c. β-carotene supplements cannot be manufactured cheaply enough. d. β-carotene can replace vitamin E in terminating the auto-oxidation of fatty acids.
b. β-carotene is not the only health-promoting molecule in fruits and vegetables.
4. Which is retinoic acid? a. A b. B c. C d. D e. E
c. C
Imagine you are a nutritionist working in a country other than the U.S. Which is an assumption about vitamin D status that is NOT true? a. The latitude makes a difference as regards how much vitamin D can be self-synthesized. b. Customs of dress make a difference as regards how much vitamin D can be self-synthesized. c. Cow's milk is a reliable source of vitamin D in the food supply. d. Skin color makes a difference as regards how much sun is needed to synthesize vitamin D.
c. Cow's milk is a reliable source of vitamin D in the food supply.
Toxicity of which vitamin is related to increased deposition of calcium in soft tissues? a. lipoic acid b. biotin c. D d. E
c. D Vitamin D, when ingested in large amounts, is one of the most likely of all vitamins to cause overt toxicity. Manifestations of toxicity include hypercalcemia and calcinosis, the associated calcification of soft tissues including organs such as the kidneys, heart, and lungs, along with blood vessels.
For which vitamin is the Tolerable Upper Intake Level set because of increased tendency for bleeding? a. A b. D c. E d. K
c. E Vitamin E appears to be one of the least toxic of the vi- tamins, although mild gastrointestinal problems may oc- cur with intakes between 200 and 800 mg. However, it is because of an increased tendency for bleeding (due to antiplatelet effects and/or abnormal blood clotting) that a Tolerable Upper Intake Level of 1,000 mg of α-tocopherol (1,500 IU of natural RRR α-tocopherol or 1100 IU of synthetic all-rac tocopherol)/day for adults has been es- tablished by the Food and Nutrition Board
Which vitamin is associated with improved plasma membrane structure and glucose transport/metabolic control in people with type 2 diabetes? a. A b. D c. E d. K
c. E Vitamin E may also improve plasma mem- brane structure to enhance cellular glucose uptake (which is important for those with diabetes).
Would you recommend β-carotene supplementation to a smoker to decrease risk to lung cancer? a. Yes—β-carotene can quench singlet oxygen. b. Yes—smoking increases free radical formation; β-carotene can decrease free radicals. c. No—β-carotene supplements may be harmful to smokers and are their use is not advised for the general public. d. No—β-carotene supplements can cause a vitamin A toxicity and liver cirrhosis.
c. No—β-carotene supplements may be harmful to smokers and are their use is not advised for the general public. More specifically, intervention trials providing 20 mg of β-carotene (BC) along with α-tocopherol (AT) in Finland (called the ATBC trial) or 30 mg of β-carotene and 25,000 IU of vitamin A (CARET trial) showed no benefit over a placebo in cancer prevention in asbestos- exposed workers and in people with a long history of smoking
The majority of vitamin A is stored in the liver, while carotenoids are stored mainly in the _____ tissue. a. muscle b. eye c. adipose d. skin
c. adipose In fact, the adipose tissue, which takes up retinyl esters from chylomicrons, stores about 15% to 20% of the body's vitamin A. Carotenoids, like vitamin A, are stored mainly in the liver and adipose tissue, but some specific tissues concentrate specific carotenoids. For example, the retina of the eye is relatively rich in lutein and zeaxanthin.
Vitamin K deficiency in adults is most likely due to: a. oxalic acid in food. b. achlorhydria. c. antibiotic therapy. d. a high-fiber diet.
c. antibiotic therapy. People consuming vitamin K-poor diets and on pro- longed sulfonamides and broad-spectrum antibiotic drug therapy are at risk for vitamin K deficiency owing to the coupled effects of low dietary intake and antibiotic-induced destruction of gastrointestinal bacteria that manufacture the vitamin and contribute a source of vitamin K.
The vitamin D response element (VDRE) is found: a. on the enterocyte membrane. b. on the renal tubule. c. in the nucleus. d. in the pancreatic duct cell.
c. in the nucleus. In addition to its genomic interactions with VDRE on genes, calcitriol also appears to exert its effects through interactions with messenger (m)RNA to enhance or inhibit translation.
Formation of retinol from beta-carotene requires the presence of what B vitamin? a. ascorbic acid b. folic acid c. niacin d. pyridoxal phosphate
c. niacin Within enterocytes, retinoids also undergo metabolism. Retinal, produced from β-carotene or other carotenoids, is reduced by retinal/retinaldehyde reductase, an NADH-dependent enzyme, to retinol.
If asked about the relationship of vitamin D to autoimmune disease, the best information for a dietetic professional to provide is: a. the evidence does not support a relationship at this time. b. the evidence is only in animals, not humans. c. some evidence suggests a protective effect of vitamin D. d. take a supplement containing 2000 IU vitamin D each day.
c. some evidence suggests a protective effect of vitamin D. Some autoimmune conditions, including rheumatoid arthritis, Crohn's disease, multiple sclerosis, and type 1 diabetes mellitus, have been linked with inadequate vitamin D status. Protective effects against developing some of these diseases also have been found with the use of vitamin D supplements in amounts up to about 50 μg (2,000 IU) daily. These findings are thought to be linked (at least partially) with vitamin D's role in immunity. Vitamin D has been shown to enhance antibody synthesis from activated B-cells and phagocytosis by macrophages. Vitamin D also regulates the expression and production of several cytokines; for example, the inflammatory cytokines interleukin (IL)2 and IL12 are down-regulated in response to vitamin D
Which vitamin is believed to function like a steroid hormone? a. choline b. vitamin A c. vitamin D d. vitamin E
c. vitamin D
Choose the correct order of the phrases below to explain the response of the body to a decline in serum calcium levels. Choose the BEST answer. 1. Increased release of PTH 2. Decreased release of PTH 3. Increased synthesis of calbindin 4. Increased synthesis of 1,25-(OH)2 D3 5. Increased bone absorption 6. Increased calcium absorption 7. Decreased bone resorption 8. Increased calcium excretion 9. Increased bone resorption a. 1, 5, 4, 8 b. 1, 3, 5, 9 c. 2, 3, 9, 6 d. 1, 4, 3, 6
d. 1, 4, 3, 6 Increased release of PTH Increased synthesis of 1,25-(OH)2 D3 Increased synthesis of calbindin Increased calcium absorption Low serum calcium concentrations, i.e., <8.5 mg/dL initially stimulates the secretion of PTH from the parathyroid gland through activation of calcium-sensing receptors. The PTH, in turn, travels to the kidneys, where it stimulates 1-hydroxylase to convert 25-OH D to calcitriol. Calbindin is a vitamin D-responsive gene in many tissues, in particular the thick intestine, where it has a clear function in mediating calcium absorption. In the brain, its synthesis is independent of vitamin-D.
What % of vitamin D from the diet is absorbed? a. 20 b. 30 c. 40 d. 50
d. 50 About 50% of dietary vitamin D is absorbed. Although the rate of absorption is most rapid in the duodenum and jejunum, the largest amount of vitamin D is absorbed in the distal small intestine.
Choose the correct statement about the quenching of singlet oxygen by carotenoids. a. Carotenoids donate an electron to the singlet oxygen to make it stable. b. Carotenoids covalently bond with the singlet oxygen to make it stable. c. Carotenoids donate energy so that the excited electron returns to its orbital. d. Carotenoids absorb the extra energy that is held by the singlet oxygen.
d. Carotenoids absorb the extra energy that is held by the singlet oxygen. Quenching is a process by which electronically excited molecules or atoms, such as singlet molecular oxygen, are inactivated. Singlet molecular ox- ygen possesses higher energy and is more reactive than ground state molecular oxygen, which typically exists in triplet (3O2) rather than singlet (1O2) form. The singlet oxygen (1O2) transfers its excitation energy and returns to the ground state (3O2), and the carotenoid receiving the energy enters an excited state.
5. Which is β-carotene? a. A b. B c. C d. D e. E
d. D
What vitamin is associated with diminished proliferation and enhanced differentiation of cells, which serves as a basis for its use as treatment of skin diseases such as psoriasis? a. A b. E c. K d. D
d. D The local presence of the calcitriol within many non- calcium regulating tissues is thought to help maintain normal cell growth, differentiation, and proliferation and, in some tissues, prevent malignancy (by down-regulating cancer cell growth and inducing apoptosis if needed). Vitamin D typically promotes differentiation and inhibits proliferation in tissues. Some examples of cells affected by vitamin D include premyeloid white blood cells and stem cells, which differentiate into macrophages and monocytes in the presence of adequate calcitriol. Calcitriol also induces cell differentiation of stem cell monocytes in the bone marrow, which become mature osteoclasts.
Which fat-soluble vitamin appears to operate as a coenzyme that modifies proteins to bind with calcium? a. A b. β-carotene c. E d. K
d. K
Which of the fat-soluble vitamins is consumed in the form of phylloquinone from plant foods? a. A b. D c. E d. K
d. K Dietary vitamin K is provided mostly as phylloquinone from ingestion of plant foods. The richest vegetable sources and the main dietary sources of vitamin K include leafy green vegetables, especially collards, spinach, turnip greens, some salad greens, and broccoli.
For which vitamin is a severe deficiency associated with an increased tendency for bleeding? a. A b. D c. E d. K
d. K Severe vitamin K deficiency is associated with bleeding episodes (hemorrhage). The undercarboxylated blood- clotting factors cannot effectively bind calcium and interact with cell membrane phospholipids exposed on tissue injury, an interaction necessary for thrombin generation and clot formation.
Choose the ONE correct statement. a. Beta-carotene is hydrolyzed in the jejunum before it is absorbed. b. Retinol does not need to form a micelle to cross the USW. c. Beta-carotene dioxygenase activity occurs in the lumen of the ileum. d. Retinol must be re-esterified to be carried in the chylomicron.
d. Retinol must be re-esterified to be carried in the chylomicron. Additionally, the vitamin must be reesterified to enable its incorporation into chylomicrons for release into the blood.
A genetic deficiency in _____ leads to a vitamin E deficiency syndrome. a. RRR alpha-tocopherol b. gamma-tocotrienol c. tocopherol carrier protein in the jejunum d. alpha-tocopherol transfer protein in the liver
d. alpha-tocopherol transfer protein in the liver It is α-tocopherol transfer protein (αTTP), which is made in the liver (among other tissues), that transfers tocopherol (RRR α-tocopherol preferentially) into VLDLs, which enable distribution of the vitamin to tissues. A deficiency or absence of αTTP caused by gene defects leads to a vitamin E deficiency. It is because of the specificity of αTTP that other forms of the vitamin are not resecreted into the circulation. Thus, α-tocopherol is the primary form of vitamin E found in the blood; normal plasma α-tocopherol (bound within lipoproteins) concentrations range from about 5 to 20 μg/mL.
Which vitamin D molecule would you expect to see in fortified foods? a. ergocalciferol - vitamin D2 b. calcidiol - 25-OH D3 c. calcitriol - 1,25-OH2 D3 d. cholecalciferol - vitamin D3
d. cholecalciferol - vitamin D3 Yet, because so few foods in the United States contain much vitamin D, selected foods, including milk, yogurt, cheese, butter, and margarine as well as some orange juice, breads, and breakfast cereals, may be fortified with the vitamin, usually as D3 but sometimes as D2. In the United States, for example, milk and orange juice may be fortified with 2.5 μg (100 IU) of vitamin D3/cup.
Choose the non-genomic effect of vitamin D. a. increased synthesis of calbindin b. bone accretion c. rapid calcium absorption d. intracellular cytosolic signal transduction
d. intracellular cytosolic signal transduction Many nongenomic actions of calcitriol are mediated by the activation of signal transduction pathways (also called intracellular signaling) linked to cell membranes. The binding of calcitriol to cell membrane receptors in selected tissues (especially intestine, parathyroid, liver, and pancreatic β-cells) triggers a series of events through signal transduction pathways to evoke relatively rapid (often within minutes or seconds) changes in some body processes.
Which is the strongest antioxidant? a. beta-carotene b. alpha-tocopherol c. beta-cryptoxanthin d. lycopene
d. lycopene Although most studies have focused on β-carotene, lycopene (in chemical assays) has been shown to be the strongest antioxidant. Lycopene appears to have the highest rate con- stant (i.e., ability to react or complex) and is a more effec- tive quencher of singlet oxygen than other carotenoids.
Which symptom of a vitamin A deficiency is most likely responsible for deficiency-related deaths? a. its function as a teratogen b. poor cellular differentiation and growth c. keratinization of the cornea d. severe infections
d. severe infections Selected signs and symptoms of deficiency include anorexia, retarded growth, increased susceptibility to infections, obstruction and enlargement of hair follicles, keratinization of epithelial cells of the skin with accompanying failure of normal differentiation, and numerous ocular (eye) effects
It's a good thing that milk is fortified with vitamin D so that we can consume the RDA if we drink the recommended number of glasses of milk each day. The DRI for 9-69 year olds is 600 IU (15 μg). This equals _____ cups of milk. a. two b. three c. four d. six
d. six 15μg (recommended)/2.5 μg (per cup of milk) = 6 cups The recommendations, which assume minimal sun exposure, suggest an intake of 600 IU (15 μg) of vitamin D for children (age 1 year and older), adolescents, and adults including women who are pregnant or lactating. In the United States, for example, milk and orange juice may be fortified with 2.5 μg (100 IU) of vitamin D3/cup.
