1, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. C marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"F"
"C marks the average requirement."
"The diagram shows the distribution of requirements for a nutrient. A marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"F"
"A marks the lower threshold intake."
2, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. B marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"T"
"B marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"The diagram shows the distribution of requirements for a nutrient. B marks the average requirement."
"F"
"B marks the Reference Nutrient Intake (or Recommended Daily Amount)."
3, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. B marks the lower threshold intake."
"F"
"B marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"The diagram shows the distribution of requirements for a nutrient. A marks the lower threshold intake."
"T"
"A marks the lower threshold intake."
4, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. At A the requirements of 97.5% of the population will have been met."
"F"
"A is the lower threshold intake, a level at which the requirements of only 2.5% of the population have been met."
"The diagram shows the distribution of requirements for a nutrient. At A the requirements of 2.5% of the population will have been met."
"T"
"A is the lower threshold intake, a level at which the requirements of only 2.5% of the population have been met."
5, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. At B the requirements of 97.5% of the population will have been met."
"T"
"B is the Reference Nutrient Intake (or Recommended Daily Amount); it is the level of intake at which the requirements of 97.5% of the population have been met."
"The diagram shows the distribution of requirements for a nutrient. At B the requirements of only 2.5% of the population will have been met."
"F"
"B is the Reference Nutrient Intake (or Recommended Daily Amount); it is the level of intake at which the requirements of 97.5% of the population have been met."
6, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. At C the requirements of 97.5% of the population will have been met."
"F"
"C is the average requirement, a level at which the requirements of 50% of the population have been met."
"The diagram shows the distribution of requirements for a nutrient. At C the requirements of 50% of the population will have been met."
"T"
"C is the average requirement, a level at which the requirements of 50% of the population have been met."
7, DRV1.bmp
"The diagram shows the distribution of requirements for a nutrient. A person with an intake lower than point B will be deficient."
"F"
"B is the Reference Nutrient Intake (or Recommended Daily Amount), an intake that is greater than the requirement for 97.5% of the population, so a person with an intake below this will not necessarily be deficient."
"The diagram shows the distribution of requirements for a nutrient. A person with an intake lower than point B will be deficient."
"F"
"B is the Reference Nutrient Intake (or Recommended Daily Amount), an intake that is greater than the requirement for 97.5% of the population, so a person with an intake below this will not necessarily be deficient."
8, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. C marks the average requirement."
"F"
"C marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"The figure shows the cumulative distribution of requirements for a nutrient. B marks the average requirement."
"T"
"At B the requirements of 50% of the population have been met - this is the average requirement."
9, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. A marks the average requirement."
"F"
"A marks the lower reference nutrient intake."
"The figure shows the cumulative distribution of requirements for a nutrient. A marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"F"
"A marks the lower reference nutrient intake."
10, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. A marks lower reference nutrient intake."
"T"
"A marks the lower reference nutrient intake."
"The figure shows the cumulative distribution of requirements for a nutrient. B marks the Reference Nutrient Intake (or Recommended Daily Amount)."
"F"
"At B the requirements of 50% of the population have been met - this is the average requirement."
11, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. At point A the requirement of 97.5% of the population has been met."
"F"
"At A the requirement of only 2.5% of the population has been met."
"The figure shows the cumulative distribution of requirements for a nutrient. At point C the requirement of 97.5% of the population has been met."
"T"
"This is the Reference Nutrient Intake (or Recommended Daily Amount), the intake at which the requirement of 97.5% of the population has been met."
12, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. At point A the requirement of only 2.5% of the population has been met."
"T"
"At A the requirement of only 2.5% of the population has been met - this is the lower threshold intake."
"The figure shows the cumulative distribution of requirements for a nutrient. At point B the requirement of 50% of the population has been met."
"T"
"B marks the average requirement, a level of intake at which the requirement of 50% of the population has been met."
13, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. For an individual whose intake is at point C there is a 97.5% probability that this intake is adequate to meet his / her requirement."
"T"
"At point C the requirements of 97.5% of the population have been met, so there is a 97.5% probability that this level of intake is adequate to meet the requirements of an individual."
"The figure shows the cumulative distribution of requirements for a nutrient. For an individual whose intake is at point B there is a 97.5% probability that this intake is adequate to meet his / her requirement."
"F"
"At point B the requirements of 50% of the population have been met, so there is a 50% probability that this level of intake is adequate to meet the requirements of an individual."
14, DRV2.bmp
"The figure shows the cumulative distribution of requirements for a nutrient. For an individual whose intake is at point C there is a 2.5% probability that this intake is adequate to meet his / her requirement."
"F"
"At point C the requirements of 97.5% of the population have been met, so there is a 97.5% probability that this level of intake is adequate to meet the requirements of an individual."
"The figure shows the cumulative distribution of requirements for a nutrient. For an individual whose intake is at point A there is a 97.5% probability that this intake is adequate to meet his / her requirement."
"F"
"At point A the requirements of only 2.5% of the population have been met, so there is only a 2.5% probability that this level of intake is adequate to meet the requirements of an individual."
15, transam.bmp
"Pyridoxal phosphate (vitamin B6) is the coenzyme for transaminases."
"T"
"Pyridoxal phosphate at the active site of transaminases acts as an intermediate carrier of the amino group, forming pyridoxamine phosphate by reaction with the donor amino acid, then donating the amino group to the acceptor keto acid."
"Thiamin diphosphate (vitamin B1) is the coenzyme for transaminases."
"F"
"Pyridoxal phosphate, which is vitamin B6, at the active site of transaminases acts as an intermediate carrier of the amino group, forming pyridoxamine phosphate by reaction with the donor amino acid, then donating the amino group to the acceptor keto acid."
16, transam.bmp
"Riboflavin phosphate (vitamin B2) is the coenzyme for transaminases."
"F"
"Pyridoxal phosphate, which is vitamin B6, at the active site of transaminases acts as an intermediate carrier of the amino group, forming pyridoxamine phosphate by reaction with the donor amino acid, then donating the amino group to the acceptor keto acid."
"Vitamin B12 is the coenzyme for transaminases."
"F"
"Pyridoxal phosphate, which is vitamin B6, at the active site of transaminases acts as an intermediate carrier of the amino group, forming pyridoxamine phosphate by reaction with the donor amino acid, then donating the amino group to the acceptor keto acid."
17, pyrdh.bmp
"Pyruvate dehydrogenase is a thiamin (vitamin B1) dependent enzyme."
"T"
"This is why thiamin (vitamin B1) deficiency results in impaired carbohydrate metabolism."
"In thiamin (vitamin B1) deficiency pyruvate accumulates in muscle and there is acidosis."
"T"
"As a result of impaired pyruvate dehydrogenase activity there is a considerable increase in plasma concentrations of both pyruvate and lactate, leading to significant acidosis." 
18, pyrdh.bmp
"In thiamin (vitamin B1) deficiency pyruvate cannot be converted to acetyl CoA."
"T"
"Pyruvate dehydrogenase is a thiamin dependent enzyme."
"In thiamin (vitamin B1) deficiency pyruvate formed in muscle cannot be transaminated to alanine."
"F"
"Transaminases are vitamin B6 dependent; their activity is not affected by thiamin (vitamin B1) deficiency. There will be increased transamination to alanine as a result of the accumulation of pyruvate." 
19, blank.bmp
"The enzyme transketolase in the pentose phosphate pathway is thiamin (vitamin B1) dependent."
"T"
"Transketolase is indeed a thiamin-dependent enzyme. Measurement of transketolase activity in red blood cells, or better, measurement of its saturation with its coenzyme, provides a sensitive index of thiamin nutritional status."
"The nerve damage of thiamin (vitamin B1) deficiency is at least partially due to impairment of the activity of the pentose phosphate pathway."
"T"
"In both the time of development of nerve damage in thiamin deficiency and also the anatomical regions of the brain affected there is a good correlation between impairment of transketolase activity in the pentose phosphate pathway and the development of neurological damage." 
20, TCAC3.bmp
"This reaction is catalysed by a thiamin-dependent multi-enzyme complex, like that of pyruvate dehydrogenase."
"T"
"The ketoglutarate dehydrogenase multi-enzyme complex is closely similar to the pyruvate dehydrogenase multi-enzyme complex, and is indeed thiamin dependent."
"Because this reaction is thiamin (vitamin B1) dependent, the activity of the citric acid cycle is severely impaired in thiamin deficiency."
"F"
"Although the activity of ketoglutarate dehydrogenase is indeed impaired in thiamin deficiency, the citric acid cycle continues more or less as normal. There is an alternative, thiamin-independent, pathway for conversion of ketoglutarate to succinate, by way of transamination to glutamate and decarboxylation to gamma-aminobutyrate (GABA)." 
21, TCAC8.bmp
"The reaction of pyruvate carboxylase is essential for gluconeogenesis from lactate in the liver."
"T"
"Lactate is oxidized to pyruvate, which must then be carboxylated to oxaloacetate for gluconeogenesis."
"Pyruvate carboxylase is a biotin-dependent enzyme."
"T"
"Like most other carboxylases, pyruvate carboxylase uses enzyme-bound biotin, which is carboxylated in the first stage of the reaction." 
22, vitB12.bmp
"A protein secreted in the gastric juice is important for the absorption of vitamin B12."
"T"
"Intrinsic factor is a vitamin B12-binding protein secreted by the gastric mucosa, which is essential for the absorption of vitamin B12."
"Achlorhydria may lead to vitamin B12 deficiency."
"T"
"Achlorhydria (failure of secretion of gastric acid) may lead to failure of vitamin B12 absorption, for two reasons: (a) gastric acid is important to release vitamin B12 that is bound to proteins in foods; (b) intrinsic factor is secreted by the same cells as secreted gastric acid, and loss of these cells leads to loss of both acid secretion and intrinsic factor secretion."
23, blank.bmp
"If an enzyme requires a coenzyme or prosthetic group, then the enzyme protein alone is known as the holo-enzyme." 
"F"
"The holo-enzyme is the active enzyme, consisting of both the protein and the prosthetic group. The protein alone, without its prosthetic group, is the apo-enzyme, which is catalytically inactive."
"If an enzyme requires a coenzyme or prosthetic group, then the enzyme protein alone is known as the apo-enzyme." 
"T"
"The holo-enzyme is the active enzyme, consisting of both the protein and the prosthetic group. The protein alone, without its prosthetic group, is the apo-enzyme, which is catalytically inactive."
24, blank.bmp
"The apo-enzyme is catalytically inactive." 
"T"
"For an enzyme that requires a prosthetic group, the enzyme protein without the prosthetic group is known as the apo-enzyme, and is catalytically inactive."
"The apo-enzyme is catalytically active." 
"F"
"For an enzyme that requires a prosthetic group, the enzyme protein without the prosthetic group is known as the apo-enzyme, and is catalytically inactive."
25, blank.bmp
"The holo-enzyme is catalytically inactive." 
"F"
"The holo-enzyme is the enzyme protein plus its prosthetic group, and is catalytically active."
"The holo-enzyme is catalytically active." 
"T"
"The holo-enzyme is the enzyme protein plus its prosthetic group, and is catalytically active."
26, retinol.bmp
"Vitamin A has a role in vision, as retinaldehyde."
"T"
"Retinaldehyde forms the prosthetic group of the visual pigment, rhodopsin."
"In vitamin A deficiency there is impaired adaptation to dim light."
"T"
"Retinaldehyde forms the prosthetic group of the visual pigment, rhodopsin, and in vitamin A deficiency it takes longer to become accustomed to dim light because of a lack of retinaldehyde to reform rhodopsin after it has been bleached by light."
27, retinol.bmp
"Although retinol and retinaldehyde are readily interconvertible, oxidation of retinaldehyde to retinoic acid is irreversible."
"T"
"Retinoic acid cannot be reduced to retinaldehyde. This means that retinoic acid will not support the functions of vitamin A in vision."
"Retinoic acid cannot support the functions of vitamin A in vision."
"T"
"Retinoic acid cannot be reduced to retinaldehyde, which is required as the prosthetic group of the visual pigment rhodopsin. This means that retinoic acid will not support the functions of vitamin A in vision."
28, retinol.bmp
"Retinaldehyde cannot be reduced to retinol."
"F"
"The oxidation of retinol to retinaldehyde is readily reversible. Indeed, reduction of retinaldehyde formed from carotene is the main metabolic source of retinol."
"Retinaldehyde cannot be oxidized to retinoic acid."
"F"
"Retinaldehyde can readily be oxidized to retinoic acid; indeed this is the major source of retinoic acid. However, retinoic acid cannot be reduced to retinaldehyde, which is required as the prosthetic group of the visual pigment rhodopsin. This means that retinoic acid will not support the functions of vitamin A in vision."
29, retinoic.bmp
"9-cis-Retinoic acid binds to the retinoic acid receptor (RAR)."
"F"
"9-cis-Retinoic acid binds to the retinoid X receptor (RXR)."
"All trans-retinoic acid binds to the retinoic acid receptor (RAR)."
"T"
"All trans-retinoic acid binds to the retinoic acid receptor (RAR) and acts to modulate gene expression."
30, retinoic.bmp
"The retinoic acid receptor (RAR) with all-trans-retinoic acid bound can dimerize with the retinoid X receptor with 9-cis-retinoic acid bound."
"T"
"The retinoic acid receptor (RAR) with all-trans-retinoic acid bound can indeed form heterodimers with the retinoid X receptor with 9-cis-retinoic acid bound."
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can dimerize with the retinoic acid receptor with all-trans-retinoic acid bound."
"T"
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can indeed form heterodimers with the retinoic acid receptor with all-trans-retinoic acid bound."
31, retinoic.bmp
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can dimerize with the vitamin D receptor."
"T"
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can indeed form heterodimers with the vitamin D receptor; this is probably essential for the nuclear functions of vitamin D."
"The retinoic acid receptor (RAR) with all trans-retinoic acid bound can dimerize with the vitamin D receptor."
"F"
"It is the retinoid X receptor (RXR) that forms heterodimers with the vitamin D receptor."
32, retinoic.bmp
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can dimerize with the thyroid hormone receptor."
"T"
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can indeed form heterodimers with the thyroid hormone receptor; this is probably essential for the nuclear functions of thyroid hormone."
"The retinoic acid receptor (RAR) with all trans-retinoic acid bound can dimerize with the thyroid hormone receptor."
"F"
"It is the retinoid X receptor (RXR) that forms heterodimers with the thyroid hormone receptor."
32, retinoic.bmp
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can dimerize with a variety of other nuclear-acting receptors."
"T"
"The retinoid X receptor (RXR) with 9-cis-retinoic acid bound can indeed form heterodimers with a number of other nuclear-acting receptors; this is probably essential for their function."
"The retinoic acid receptor (RAR) with all trans-retinoic acid bound can dimerize with a variety of other nuclear-acting receptors."
"F"
"It is the retinoid X receptor (RXR) that forms heterodimers with a variety of other nuclear-acting receptors."
33, carot.bmp
"Oxidative cleavage of beta-carotene by carotene dioxygenase can give rise to 2 mol of retinaldehyde, and therefore 1 mol of dietary beta-carotene is equivalent to 2 mol of dietary retinol."
"F"
"Although oxidative cleavage of beta-carotene by carotene dioxygenase can theoretically give rise to 2 mol of retinaldehyde, in practice the yield is very much lower, and 6 g of beta-carotene is equivalent to 1 g of retinol."
"The enzymes that catalyse the oxidative cleavage of beta-carotene to retinaldehyde may act centrally or excentrically, so that the yield of retinaldehyde from beta-carotene is very much lower than might be expected."
"T"
"Although central oxidative cleavage of beta-carotene by carotene dioxygenase can give rise to 2 mol of retinaldehyde, in practice the yield is very much lower, at least partly because a second isoenzyme catalyses excentric cleavage, yielding products that can be oxidized to retinoic acid, but cannot be metabolized to yield retinaldehyde."
33, carot.bmp
"Oxidative cleavage of beta-carotene by carotene dioxygenase can give rise to 2 mol of retinaldehyde, and therefore 1 mol of dietary beta-carotene is equivalent to 2 mol of dietary retinol."
"F"
"Nutritionally, it requires 6 g of beta-carotene to be equivalent to 1 g of dietary retinol; part of this is explained by the low activity of the intestinal mucosal carotene dioxygenase. It is more or less saturated at normal intakes of carotene, and a considerable amount of unmetabolized carotene is absorbed. This may or may not be oxidized to yield retinaldehyde in the liver and other tissues."
"Oxidative cleavage of beta-carotene by carotene dioxygenase can give rise to 2 mol of retinaldehyde, and therefore 1 g of dietary beta-carotene is equivalent to 1 g of dietary retinol."
"F"
"Nutritionally, it requires 6 g of beta-carotene to be equivalent to 1 g of dietary retinol; part of this is explained by the low activity of the intestinal mucosal carotene dioxygenase. It is more or less saturated at normal intakes of carotene, and a considerable amount of unmetabolized carotene is absorbed. This may or may not be oxidized to yield retinaldehyde in the liver and other tissues."
34, vitD.bmp
"Vitamin D acts to regulate gene expression for calcium-binding proteins."
"T"
"Vitamin D acts to regulate gene expression, especially of calcium-binding proteins."
"The vitamin D receptor forms a heterodimer with the retinoid X receptor for activity."
"T"
"The vitamin D receptor acts as a heterodimer with the retinoid X receptor."
35, vitD.bmp
"Vitamin D regulates plasma calcium by increasing the intestinal absorption of calcium."
"T"
"One of the main actions of vitamin D is induction of the intestinal calcium binding protein that is required for calcium absorption. It also activates intestinal calcium transport."
"Vitamin D increases intestinal absorption of calcium by both induction of the intestinal calcium binding protein and also activation of intestinal calcium transport."
"T"
"Vitamin D has both a nuclear action (induction of the intestinal calcium binding protein) and also a non-genomic action (recruitment and activation of the cell membrane calcium transport protein) in intestinal mucosal cells."
36, vitD.bmp
"Vitamin D regulates plasma calcium by increasing the renal excretion of calcium."
"F"
"Quite the reverse. Vitamin D stimulates the resorption of calcium in the distal renal tubule, and so reduces urinary excretion."
"Vitamin D regulates plasma calcium by decreasing the renal excretion of calcium."
"T"
"Vitamin D stimulates the resorption of calcium in the distal renal tubule, and so reduces urinary excretion."
37, vitD.bmp
"Vitamin D regulates plasma calcium by increasing the mobilization of bone mineral, as a result of increased osteoclast activity."
"T"
"Vitamin D acts to increase plasma calcium, and its initial action is to increase mobilization of bone mineral by stimulation of osteoclast activity. It acts later to recruit and activate osteoblasts, which deposit new bone mineral."
"Vitamin D regulates plasma calcium by decreasing the mobilization of bone mineral."
"F"
"Vitamin D acts to increase plasma calcium, and its initial action is to increase mobilization of bone mineral by stimulation of osteoclast activity. It acts later to recruit and activate osteoblasts, which deposit new bone mineral."
38, vitD.bmp
"Because of its role in regulating the expression of calcium binding proteins, vitamin D is required for control of the secretion of insulin, thyroid and parathyroid hormones."
"T"
"Secretion of peptide hormones such as insulin, thyroid and parathyroid hormones is calcium dependent, and expression of the calcium binding proteins involved in the process is regulated by vitamin D."
"Vitamin D deficiency will result in impaired immune system function."
"T"
"Vitamin D has a role in regulating the differentiation and function of immune system cells, and therefore deficiency may indeed result in impaired immune responses."
39, vitD.bmp
"There is no dietary requirement for vitamin D, since it can be synthesized in the skin if there is adequate exposure to sunlight."
"T"
"Although it was discovered as a result of studies of dietary deficiency, vitamin D can indeed be synthesized in the skin if there is adequate exposure to sunlight, and there is probably no need for a dietary intake."
"Excessive exposure to sunlight is dangerous because vitamin D, which is synthesized in the skin on exposure to sunlight, is toxic in excess."
"F"
"Although vitamin D is indeed toxic in excess, excessive sunlight exposure does not result in vitamin D toxicity - partly because the supply of the precursor, 7-dehydrocholesterol, is limited, and partly because previtamin D, formed from 7-dehydrocholesterol on uv irradiation, undergoes a further light-catalysed reaction to tachysterol, which is not a precursor for vitamin D synthesis."
40, vitD.bmp
"Cholecalciferol, either formed in the skin, or taken in in the diet, does not activate the vitamin D receptor."
"T"
"Cholecalciferol undergoes two hydroxylations, one in the liver and the other in the kidney, to form the active hormone calcitriol (1,25-dihydroxy-vitamin D)."
"Cholecalciferol, either formed in the skin, or taken in in the diet, activates the vitamin D receptor directly."
"F"
"Cholecalciferol undergoes two hydroxylations, one in the liver and the other in the kidney, to form the active hormone calcitriol (1,25-dihydroxy-vitamin D)."
41, vitD.bmp
"The metabolic fate of calcidiol (25-hydroxycholecalciferol) in the kidney is regulated by the state of calcium balance."
"T"
"In the kidney calcidiol may undergo either 1-hydroxylation to yield the active hormone calcitriol (1,25-dihydroxy-vitamin D), or 24-hydroxylation to yield an inactive product. The two enzymes involved are regulated by parathyroid hormone, whose secretion in turn is regulated by the state of calcium balance."
"Although vitamin D regulates plasma calcium, its metabolism is not affected by the state of calcium balance."
"F"
"In the kidney calcidiol may undergo either 1-hydroxylation to yield the active hormone calcitriol (1,25-dihydroxy-vitamin D), or 24-hydroxylation to yield an inactive product. The two enzymes involved are regulated by parathyroid hormone, whose secretion in turn is regulated by the state of calcium balance."
42, vitD.bmp
"Vitamin D deficiency in children and adolescents leads to the development of rickets."
"T"
"At times of rapid growth vitamin D deficiency leads to the formation of under-mineralized bone. This is rickets."
"Vitamin D deficiency in children and adolescents leads to the development of osteomalacia."
"F"
"At times of rapid growth vitamin D deficiency leads to the formation of under-mineralized bone. This is rickets. Osteomalacia is progressive demineralization of bone in vitamin D deficient adults."
43, vitD.bmp
"Vitamin D deficiency in adults leads to the development of osteomalacia."
"T"
"Osteomalacia is progressive demineralization of bone in vitamin D deficient adults, as a result of impaired replacement of bone mineral that has been mobilized by osteoclast activity."
"Vitamin D deficiency in adults leads to the development of rickets."
"F"
"At times of rapid growth vitamin D deficiency leads to the formation of under-mineralized bone. This is rickets. In vitamin D deficient adults what is seen is osteomalacia - progressive demineralization of bone as a result of impaired replacement of bone mineral that has been mobilized by osteoclast activity."
44, vitD.bmp
"Vitamin D deficiency in adults and children can be diagnosed by measuring bone density by X-ray."
"T"
"The poor mineralization of bone in vitamin D deficiency, whether it is due to rickets in children or osteomalacia in adults, means that bones are less opaque to X-rays, so it is indeed easy to diagnose deficiency by measurement of bone density by X-ray techniques."
"Preclinical vitamin D deficiency in adults and children can be detected by measuring plasma alkaline phosphatase activity."
"T"
"Plasma alkaline phosphatase activity is indeed increased in vitamin D deficiency, and this provides a way of detecting (preclinical) vitamin D deficiency before there is any significant loss of bone mineral."
45, vitE.bmp
"The diagram shows a significant negative correlation between death from coronary heart disease and plasma vitamin E. This means that vitamin E is a cause of coronary heart disease."
"F"
"Quite the contrary - a negative correlation like this suggests that vitamin E may be protective against coronary heart disease."
"The diagram shows a significant negative correlation between death from coronary heart disease and plasma vitamin E. This suggests that vitamin E may be preventive against coronary heart disease."
"T"
"Although data like these do not provide proof, they do indeed suggest that vitamin E may be protective against coronary heart disease."
46, vitE.bmp
"The diagram shows a significant negative correlation between death from coronary heart disease and plasma vitamin E. Vitamin E provides protection against radical damage to plasma lipoproteins because it forms a stable radical."
"T"
"The radical that is formed when vitamin E reacts with a lipid peroxide is relatively stable, and survives long enough to undergo enzymic or non-enzymic reduction to yield non-radical products."
"The diagram shows a significant negative correlation between death from coronary heart disease and plasma vitamin E. Although vitamin E is generally considered to be an antioxidant, it may also be a pro-oxidant."
"T"
"An antioxidant such as vitamin E acts by forming a radical that is relatively stable, and survives long enough to undergo enzymic or non-enzymic reduction to yield non-radical products. This means that the radical may also survive to penetrate deeper into tissues or plasma lipoproteins and perpetuate radical damage. Any antioxidant can also have pro-oxidant actions."
47, vitEstruct.bmp
"There are two families of compounds with vitamin E activity, the tocopherols and the tocotrienols. Both are antioxidants because they can form stable radicals."
"T"
"A lone electron can readily be delocalized in the ring structure of tocopherols and tocotrienols, and therefore they can form a stable radical that persists long enough to undergo metabolism to non-radical compounds."
"There are two families of compounds with vitamin E activity, the tocopherols and the tocotrienols. Both act to reduce endogenous cholesterol synthesis."
"F"
"The tocotrienols act to down-regulate the rate limiting enzyme of cholesterol synthesis, hydroxymethylglutaryl CoA reductase (HMG CoA reductase), but the tocopherols do not."
48, vitEstruct.bmp
"Chemically synthesized alpha-tocopherol is identical to, and hence biologically the same as, alpha-tocopherol extracted from natural sources."
"F"
"The side-chain of tocopherol has three centres of asymmetry, and chemical synthesis yields a mixture of isomers, which have different biological activity. In alpha-tocopherol extracted from natural sources all three asymmetric centres have the R-configuration."
"Chemically synthesized alpha-tocopherol is not identical to, and hence not biologically the same as, alpha-tocopherol extracted from natural sources."
"T"
"The side-chain of tocopherol has three centres of asymmetry, and chemical synthesis yields a mixture of isomers, which have different biological activity. In alpha-tocopherol extracted from natural sources all three asymmetric centres have the R-configuration."
49, vitEstruct.bmp
"Vitamin E deficiency in experimental animals leads to sterility. In human beings vitamin E enhances sexual potency."
"F"
"This is part of the unfounded mythology surrounding vitamin E. Although severe vitamin E deficiency indeed leads to sterility in experimental animals, there is no evidence that vitamin E has any effects on sexual potency in human beings."
"Vitamin E requirements depend on the dietary intake of polyunsaturated fatty acids."
"T"
"Requirements for vitamin E depend to a considerable extent on intake of polyunsaturated fatty acids, because of the antioxidant actions of the vitamin in inactivating the peroxides formed by oxidation of polyunsaturated fatty acids in membranes and plasma lipoproteins. The nervous system damage caused by vitamin E deficiency is exacerbated by high intakes of polyunsaturated fatty acids."
50, vitK.bmp
"There is no need for a dietary intake of vitamin K because it is synthesized by intestinal bacteria."
"F"
"Although intestinal bacteria synthesize menaquinones, some of which can be absorbed and converted to active compounds in the body, it is possible to induce signs of vitamin K deficiency by simple dietary restriction so bacterial synthesis cannot meet requirements. Although about half the menaquinones in the liver are of bacterial origin, many of these are biologically inactive."
"There is no need for a dietary intake of vitamin K because it is synthesized in the skin by exposure to sunlight."
"F"
"It is vitamin D that is synthesized in the skin on exposure to sunlight. Intestinal bacteria synthesize menaquinones, some of which can be absorbed and converted to compounds with vitamin K activity in the body. However, it is possible to induce signs of vitamin K deficiency by simple dietary restriction, so bacterial synthesis cannot meet requirements."
51, vitK.bmp
"Vitamin K nutritional status can be assessed by measuring blood clotting time."
"T"
"Vitamin K is required for the synthesis of carboxyglutamate in prothrombin and other blood clotting proteins. In deficiency there is synthesis of undercarboxylated clotting proteins, which have little activity, and measurement of clotting time can indeed be used to assess vitamin K nutritional status." 
"Vitamin K nutritional status can be assessed using antibodies raised against preprothrombin, the precursor of the blood clotting protein prothrombin."
"T"
"Vitamin K is required for the synthesis of carboxyglutamate in prothrombin and other blood clotting proteins. In deficiency there is synthesis of undercarboxylated clotting proteins, which have little activity. One of these is preprothrombin, which can indeed be measured using antibodies."
52, Glasyn.bmp
"Antimetabolites of vitamin K can be used to increase blood clotting time in patients at risk of thrombosis."
"T"
"Compounds that inhibit reaction B or C in the diagram above will induce vitamin K deficiency, because it cannot be recycled. As a result there is a failure of the normal carboxylation of glutamate residues on preprothrombin and other clotting proteins, and hence an increase in blood clotting time. This is the basis of the action of most of drugs used to treat patients at risk of thrombosis as a result of over-production of clotting proteins."
"Antimetabolites of vitamin K can be used as pesticides to kill rodents"
"T"
"Compounds that inhibit reaction B or C in the diagram above will induce vitamin K deficiency, because it cannot be recycled. As a result there is a failure of the normal carboxylation of glutamate residues on preprothrombin and other clotting proteins, and hence an increase in blood clotting time. If a high enough dose is used the animals will suffer severe haemorrhage as a result of more or less complete failure of blood clotting."
53, Glasyn.bmp
"Animals that have a very high intake of vitamin K will be resistant to the action of poisons such as Warfarin."
"T"
"Compounds that inhibit reactions B and C in the diagram above will induce vitamin K deficiency, because it cannot be recycled. As a result there is a failure of the normal carboxylation of glutamate residues on preprothrombin and other clotting proteins, and hence an increase in blood clotting time. However, a very high intake of vitamin K will permit carboxylation of glutamate - the vitamin K epoxide cannot be recycled, but will be excreted."
"There is a time lag of many hours before there is any effect on blood clotting when vitamin K deficient animals or people are repleted with the vitamin."
"T"
"Vitamin K is required for the carboxylation of glutamate residues in preprothrombin to form active thrombin, and in deficiency inactive preprothrombin is secreted into the circulation. Because there is a need for new synthesis of prothrombin when vitamin K is repleted, it takes 24 hours or longer before there is an increase in blood clotting activity."
54, Glasyn.bmp
"If blood from vitamin K deficient animals or people is incubated with vitamin K normal clotting activity will be restored."
"F"
"Vitamin K is required for the carboxylation of glutamate residues in preprothrombin to form active thrombin, and in deficiency inactive preprothrombin is secreted into the circulation. Because there is a need for new synthesis of prothrombin when vitamin K is repleted, it takes 24 hours or longer before there is an increase in blood clotting activity. Adding the vitamin to preprothrombin in plasma will have no effect."
"Haemorrhagic disease of the newborn can be prevented by giving vitamin K shortly after birth."
"T"
"A small number of new-born infants are at risk of haemorrhage as a result of vitamin K deficiency, and it is generally recommended that all new-born infants should be given a prophylactic dose of the vitamin."
55, thiamin.bmp
"Thiamin (vitamin B1) nutritional status can be assessed by measurement of the transketolase activation coefficient in red blood cells."
"T"
"Thiamin diphosphate is the coenzyme of transketolase, which occurs in red blood cells. In deficiency there is an excess of (catalytically inactive) apo-enzyme, which can be activated by incubating with thiamin diphosphate in vitro."
"Thiamin (vitamin B1) nutritional status can be assessed by measurement plasma lactate and pyruvate after a test dose of glucose."
"T"
"Thiamin diphosphate is the coenzyme for pyruvate dehydrogenase, and in deficiency its activity is much reduced. As a result both pyruvate and lactate accumulate after a test dose of glucose."
56, thiamin.bmp
"Thiamin (vitamin B1) provides the coenzyme for pyruvate carboxylase."
"F"
"Thiamin diphosphate is the coenzyme for pyruvate dehydrogenase, not pyruvate carboxylase. The coenzyme for pyruvate carboxylase is biotin"
"Thiamin (vitamin B1) provides the coenzyme for pyruvate dehydrogenase."
"T"
"Thiamin diphosphate is the coenzyme for a series of enzymes that catalyse oxidative decarboxylation; pyruvate dehydrogenase is probably the most important of these."
57, thiamin.bmp
"Thiamin (vitamin B1) provides the coenzyme for ketoglutarate dehydrogenase, and therefore in deficiency the activity of the citric acid cycle is severely impaired."
"F"
"Thiamin diphosphate is the coenzyme for a series of enzymes that catalyse oxidative decarboxylation, including ketoglutarate dehydrogenase. However, deficiency does not impair the citric acid cycle to any significant extent, because there is an alternative pathway, the GABA shunt, to bypass the reaction of ketoglutarate dehydrogenase."
"Thiamin (vitamin B1) provides the coenzyme for pyruvate, and therefore in deficiency the metabolism of glucose is severely impaired."
"T"
"Thiamin diphosphate is the coenzyme for pyruvate dehydrogenase, and in deficiency its activity is much reduced. As a result both pyruvate and lactate accumulate, and this can result in life-threatening acidosis."
58, thiamin.bmp
"Beriberi is due to thiamin (vitamin B1) deficiency. It is a peripheral neuropathy that may or may not be associated with oedema."
"T"
"Beriberi is peripheral neuropathy due to thiamin deficiency; in wet beriberi there is oedema (fluid retention) in addition to the nerve damage."
"Beriberi is due to thiamin (vitamin B1) deficiency. Acute cardiac beriberi involves oedema and right-sided heart failure without any signs of peripheral neuropathy."
"T"
"Acute thiamin deficiency (commonly associated with alcohol abuse) can lead to cardiac enlargement and oedema, both of which respond to thiamin, without signs of the peripheral nerve damage of classical beriberi."
59, ribofl.bmp
"Because riboflavin (vitamin B2) provides the coenzyme for a large number of enzymes involved in oxidation and reduction reactions in all energy-yielding metabolic pathways, deficiency is fatal."
"F"
"Although riboflavin phosphate and flavin adenine dinucleotide (FAD) derived from riboflavin are indeed coenzymes for a great many enzymes involved in all energy-yielding metabolic pathways, deficiency is not fatal, because there is extremely efficient recycling of the riboflavin released from catabolism of enzymes."
"Although riboflavin (vitamin B2) provides the coenzyme for a large number of enzymes involved in oxidation and reduction reactions in all energy-yielding metabolic pathways, deficiency is not fatal."
"T"
"Although riboflavin phosphate and flavin adenine dinucleotide (FAD) derived from riboflavin are indeed coenzymes for a great many enzymes involved in all energy-yielding metabolic pathways, deficiency is not fatal, because there is extremely efficient recycling of the riboflavin released from catabolism of enzymes."
60, ribofl.bmp
"Riboflavin (vitamin B2) nutritional status can be assessed by measurement of the activation coefficient of red cell glutathione reductase."
"T"
"FAD, derived from riboflavin is the coenzyme of glutathione reductase, which occurs in red blood cells. In deficiency there is an excess of (catalytically inactive) apo-enzyme, which can be activated by incubating with FAD in vitro."
"Riboflavin (vitamin B2) nutritional status can be assessed by measurement of the activation coefficient of red cell glutathione peroxidase."
"F"
"Glutathione peroxidase is not a riboflavin-dependent enzyme. It is glutathione reductase that has a coenzyme derived from riboflavin."
61, plp.bmp
"Vitamin B6 nutritional status can be assessed by measurement of red cell transaminase activation coefficient."
"T"
"Pyridoxal phosphate, derived from vitamin B6, is the coenzyme of transaminases. In deficiency there is an excess of (catalytically inactive) apo-enzyme, which can be activated by incubating with pyridoxal phosphate in vitro."
"Vitamin B6 nutritional status can be assessed by measurement of red cell transketolase activation coefficient."
"F"
"The coenzyme for transketolase is thiamin diphosphate, derived from vitamin B1. It is transaminases that are vitamin B6 dependent."
62, thiamin.bmp
"Thiamin (vitamin B1) nutritional status can be assessed by measurement of red cell transaminase activation coefficient."
"F"
"Transaminases are vitamin B6 dependent. Thiamin (vitamin B1) status can be assessed by measuring the red cell transketolase activation coefficient."
"Thiamin (vitamin B1) nutritional status can be assessed by measurement of red cell transaldolase activation coefficient."
"F"
"Transaldolase is not thiamin dependent. It is red cell transketolase that can be used to assess thiamin status."
63, TLT.bmp
"In the metabolism of tryptophan, there is normally little formation of xanthurenic and kynurenic acids because the enzyme catalysing reactions C and D has a high Km."
"T"
"Normally most metabolic flux is through reaction B, because the enzyme catalysing reactions C and D has a high Km. It is only when the activity of kynureninase (enzyme B) is low that kynurenine and hydroxykynurenine accumulate in sufficient quantity for there to be significant formation of kynurenic and xanthurenic acids."
"Induction of enzyme A will result in increased urinary excretion of kynurenic and xanthurenic acids, which might be mistaken for vitamin B6 deficiency."
"T"
"Normally most metabolic flux is through reaction B, because the enzyme catalysing reactions C and D has a high Km. It is only when the activity of kynureninase (enzyme B) is lower than that of tryptophan dioxygenase (reaction A) that kynurenine and hydroxykynurenine accumulate in sufficient quantity for there to be significant formation of kynurenic and xanthurenic acids. Kynureninase is a pyridoxal phosphate (vitamin B6) dependent enzyme, and efficiency will reduce the activity of kynureninase below that of tryptophan dioxygenase."
64, TLT.bmp
"Deficiency of vitamin B6 will result in increased urinary excretion of xanthurenic and kynurenic acids after a test dose of tryptophan."
"T"
"Kynureninase (enzyme B) is pyridoxal phosphate (vitamin B6) dependent, and in deficiency its activity falls. Normally most metabolic flux is through reaction B, because the enzyme catalysing reactions C and D has a high Km. It is only when the activity of kynureninase (enzyme B) is lower than that of tryptophan dioxygenase (reaction A) that kynurenine and hydroxykynurenine accumulate in sufficient quantity for there to be significant formation of kynurenic and xanthurenic acids."
"Oestrogens cause vitamin B6 deficiency."
"F"
"Oestrogen metabolites inhibit kynureninase (enzyme B). Normally most tryptophan metabolism is through kynureninase, because the enzyme catalysing reactions C and D has a high Km. It is only when the activity of kynureninase (enzyme B) is lower than that of tryptophan dioxygenase (reaction A) that kynurenine and hydroxykynurenine accumulate in sufficient quantity for there to be significant formation of kynurenic and xanthurenic acids. Although this occurs in vitamin B6 deficiency, because kynureninase is a pyridoxal phosphate (vitamin B6) dependent enzyme, the effect of oestrogen metabolites is unrelated to vitamin B6. It is simple inhibition of the enzyme."
65, TLT.bmp
"Inhibition of enzyme B will result in the development of pellagra, the tryptophan and niacin deficiency disease."
"T"
"Much of the requirement for NAD is met by de novo synthesis from tryptophan, via the pathway shown here. Inhibition of enzyme B will result in increased formation and excretion of xanthurenic and kynurenic acids, so that less 3-hydroxyanthranilic acid is available for NAD synthesis. This will lead to the development of pellagra."
"Women are more susceptible to pellagra in areas where tryptophan and niacin are marginal than are men because oestrogen metabolites inhibit reaction B."
"T"
"Oestrogen metabolites inhibit kynureninase (enzyme B). Much of the requirement for NAD is met by de novo synthesis from tryptophan, via the pathway shown here. Inhibition of kynureninase will result in increased formation and excretion of xanthurenic and kynurenic acids, so that less 3-hydroxyanthranilic acid is available for NAD synthesis. This will lead to the development of pellagra."
66, SAM.bmp
"Vitamin B6 nutritional status can be assessed by measuring the urinary excretion of homocysteine after a test dose of methionine."
"T"
"Enzymes B (cystathione synthetase) and C (cystathionase) are both pyridoxal phosphate (vitamin B6) dependent, and in deficiency their activity falls. Reaction A is regulated by the requirement for methionine, and therefore in vitamin B6 deficiency, after a test dose of methionine there will be a considerable accumulation of homocysteine, which is excreted in the urine."
"Vitamin B1 nutritional status can be assessed by measuring the urinary excretion of homocysteine after a test dose of methionine."
"F"
"Enzymes B (cystathione synthetase) and C (cystathionase) are both pyridoxal phosphate (vitamin B6) dependent; vitamin B1 is not involved in this pathway."
67, mma.bmp
"Reaction A is biotin-dependent."
"T"
"Reaction A is a carboxylation reaction (propionyl CoA carboxylase), and like most other carboxylations, biotin is the coenzyme."
"Reaction B is vitamin B12 dependent."
"T"
"This methylmalonyl CoA mutase, which is indeed a vitamin B12 dependent enzyme."
68, mma.bmp
"Vitamin B12 nutritional status can be assessed by measurement of methylmalonic acid excretion in the urine."
"T"
"Enzyme B (methylmalonyl CoA mutase) is a vitamin B12 dependent enzyme, and in deficiency its activity is impaired. As methylmalonyl CoA accumulates, so it is hydrolysed to liberate the CoA, and methylmalonic acid is excreted in the urine."
"Folate nutritional status can be assessed by measurement of methylmalonic acid excretion in the urine."
"F"
"Folate is not involved in this pathway. Enzyme B (methylmalonyl CoA mutase) is a vitamin B12 dependent enzyme, and in deficiency its activity is impaired. As methylmalonyl CoA accumulates, so it is hydrolysed to liberate the CoA, and methylmalonic acid is excreted in the urine."
69, vitB12.bmp
"Dietary deficiency of vitamin B12 is relatively common."
"F"
"Dietary deficiency of vitamin B12 is rare. Even strict vegetarians (Vegans) often obtain sufficient vitamin B12 from trace bacterial contamination of foods. The usual cause of vitamin B12 deficiency is a failure of absorption."
"Dietary deficiency of vitamin B12 is rare."
"T"
"Dietary deficiency of vitamin B12 is indeed rare. Even strict vegetarians (Vegans) often obtain sufficient vitamin B12 from trace bacterial contamination of foods. The usual cause of vitamin B12 deficiency is a failure of absorption."
70, folate.bmp
"Dietary deficiency of folate is relatively common."
"T"
"Dietary deficiency of folate is indeed relatively common."
"Dietary deficiency of folate is very rare."
"F"
"Dietary deficiency of folate is relatively common."
71, folate.bmp
"Supplements of folate above what could be obtained from a normal diet prevent spina bifida and neural tube defect if begun before or at the time of conception."
"T"
"Supplements of 400 g of folate, in addition to a normal intake of about 200 g per day do indeed reduce the incidence of spina bifida and neural tube defect, but only if they are started before about day 21 of pregnancy, which is when the neural tube closes."
"Supplements of folate above what could be obtained from a normal diet prevent spina bifida and neural tube defect if begin after a positive pregnancy test result."
"F"
"Supplements of 400 g of folate, in addition to a normal intake of about 200 g per day do indeed reduce the incidence of spina bifida and neural tube defect, but only if they are started before about day 21 of pregnancy, which is when the neural tube closes. This is before there would be a positive pregnancy test result."
72, folate.bmp
"Deficiency of folate results in megaloblastic anaemia."
"T"
"Folate is required for DNA synthesis, and deficiency results in release into the circulation of megaloblastic immature red blood cell precursors."
"Deficiency of folate results in microcytic hypochromic anaemia."
"F"
"Microcytic hypochromic anaemia (small and under-pigmented red blood cells) is due to iron deficiency. Folate is required for DNA synthesis, and deficiency results in release into the circulation of megaloblastic immature red blood cell precursors - megaloblastic anaemia."
73, folate2.bmp
"The metabolic function of folate is as a carrier of one-carbon fragments. All the one-carbon substituted folate derivatives shown above are freely interconvertible."
"F"
"The reduction of methylene tetrahydrofolate to methyl tetrahydrofolate is irreversible, and folate can only be liberated from methyl tetrahydrofolate by the reaction of methionine synthetase."
"Folate nutritional status can be assessed by measurement of the excretion of formiminoglutamate after a test dose of histidine."
"T"
"An intermediate in the metabolism of histidine is formiminoglutamate. This normally transfers its formimino group onto tetrahydrofolate, forming formimino-tetrahydrofolate. In folate deficiency there is insufficient folate available, and forminoglutamate accumulates and is excreted in the urine."
74, folate2.bmp
"Radioactivity from [14C] glycine may be found in DNA."
"T"
"Glycine is metabolized by a folate-dependent pathway, and the methylene tetrahydrofolate may either be used in the synthesis of TMP, which is incorporated into DNA, or may be reduced to formyl-tetrahydrofolate, which is used for the synthesis of purines, which again are incorporated into DNA."
"Radioactivity from [14C] glycine may be found in carbon dioxide."
"T"
"Glycine is metabolized by a folate-dependent pathway, and the methylene tetrahydrofolate may be reduced to formyl-tetrahydrofolate. When there is a more than adequate supply of one-carbon substituted folate, formyl-tetrahydrofolate can be oxidized to yield carbon dioxide and release free tetrahydrofolate that can be used for the catabolic reactions on the left of the diagram."
75, folate2.bmp
"Radioactivity from the [14C] methyl-tetrahydrofolate may be found in carbon dioxide."
"F"
"The reduction of methylene tetrahydrofolate to methyl tetrahydrofolate is irreversible, and the only fate of the methyl group is incorporation into methionine."
"The reaction of methionine synthetase, to form methionine from methyl tetrahydrofolate, is vitamin B12 dependent. This means that vitamin B12 deficiency may cause functional folate deficiency despite an adequate dietary intake of folate."
"T"
"Most folate is converted to methyl tetrahydrofolate during absorption, and the only way in which free folate can be released is by way of the methionine synthetase reaction. In vitamin B12 deficiency methyl folate cannot be utilized, and there is indeed functional folate deficiency."
76, mthfr.bmp
"A common genetic variant of the enzyme methylene tetrahydrofolate reductase is unstable, so that there is low activity of the enzyme in tissues. This can lead to the accumulation of excessive amounts of homocysteine."
"T"
"Methyl tetrahydrofolate is required for the remethylation of homocysteine to methionine, and if there is an impaired ability to form methyl tetrahydrofolate then homocysteine cannot be remethylated, and will indeed accumulate."
"A common genetic variant of the enzyme methylene tetrahydrofolate reductase is unstable, so that there is low activity of the enzyme in tissues. This is associated with cardiovascular disease."
"T"
"Methyl tetrahydrofolate is required for the remethylation of homocysteine to methionine, and if there is an impaired ability to form methyl tetrahydrofolate then homocysteine cannot be remethylated, and will accumulate. Elevated plasma homocysteine is a significant risk factor for cardiovascular disease. The abnormal form of methylene tetrahydrofolate reductase is found very much more often among people with cardiovascular disease than in those free from cardiovascular disease."
77, mthfr.bmp
"A common genetic variant of the enzyme methylene tetrahydrofolate reductase is unstable, so that there is low activity of the enzyme in tissues. This can lead to the accumulation of excessive amounts of homocysteine, but a high intake of folate will mask the effect of the abnormal enzyme."
"T"
"Most folate is methylated during absorption from the small intestine. Intestinal mucosal cells turn over rapidly, so an unstable enzyme is relatively unimportant. This means that people with a high intake of folate can maintain an adequate supply of methyl tetrahydrofolate despite having the unstable variant of methylene tetrahydrofolate reductase."
"A common genetic variant of the enzyme methylene tetrahydrofolate reductase is unstable, so that there is low activity of the enzyme in tissues. This can lead to the accumulation of excessive amounts of homocysteine, and a high intake of folate has no effect."
"F"
"Most folate is methylated during absorption from the small intestine. Intestinal mucosal cells turn over rapidly, so an unstable enzyme is relatively unimportant. This means that people with a high intake of folate can maintain an adequate supply of methyl tetrahydrofolate despite having the unstable variant of methylene tetrahydrofolate reductase."
78, ascorbate.bmp
"The only function of vitamin C is as a non-enzymic antioxidant."
"F"
"Although vitamin C has a significant role as an antioxidant, acting non-enzymically, it is also coenzyme for a number of enzymes, and has a clearly defined metabolic role."
"Vitamin C increases the formation of nitrosamines from amines and nitrite in the diet."
"F"
"Vitamin C, present in the stomach together with amines and nitrite, inhibits the formation of nitrosamines, which are carcinogenic. This is an additional protective role, quite apart from its antioxidant function."
79, ascorbate.bmp
"A high intake of vitamin C impairs iron absorption."
"F"
"Quite the reverse. An intake of about 25 - 50 mg of vitamin C with a meal significantly increases the absorption of inorganic iron from foods. It is, or should be, common practice to prescribe vitamin C supplements together with iron supplements to treat iron deficiency anaemia."
"A high intake of vitamin C improves iron absorption."
"T"
"An intake of about 25 - 50 mg of vitamin C with a meal significantly increases the absorption of inorganic iron from foods. It is, or should be, common practice to prescribe vitamin C supplements together with iron supplements to treat iron deficiency anaemia."
80, ascorbate.bmp
"People who are being treated for iron deficiency anaemia should not take vitamin C supplements, or take their iron tablets with orange juice."
"F"
"Quite the reverse. An intake of about 25 - 50 mg of vitamin C significantly increases the absorption of inorganic iron. It is, or should be, common practice to prescribe vitamin C supplements together with iron supplements to treat iron deficiency anaemia. A glass of orange juice will provide about 25 - 50 mg vitamin C."
"People who are being treated for iron deficiency anaemia should take vitamin C supplements or take their iron tablets with orange juice."
"T"
"An intake of about 25 - 50 mg of vitamin C significantly increases the absorption of inorganic iron. It is, or should be, common practice to prescribe vitamin C supplements together with iron supplements to treat iron deficiency anaemia. A glass of orange juice will provide about 25 - 50 mg vitamin C."
81, ascorbate.bmp
"In the copper-dependent hydroxylases (eg dopamine hydroxylase), ascorbate is reduced stoichiometrically with hydroxylation of the substrate."
"T"
"Ascorbate is the reducing agent for the copper-dependent hydroxylases, and there is indeed simple stoichiometry between substrate hydroxylated and ascorbate oxidized."
"In the copper-dependent hydroxylases (eg dopamine hydroxylase), ascorbate is not reduced stoichiometrically with hydroxylation of the substrate."
"F"
"Ascorbate is the reducing agent for the copper-dependent hydroxylases, and there is indeed simple stoichiometry between substrate hydroxylated and ascorbate oxidized."
82, ascorbate.bmp
"In the iron-dependent ketoglutarate-linked hydroxylases (eg proline hydroxylase), ascorbate is reduced stoichiometrically with hydroxylation of the substrate."
"F"
"The iron in iron-dependent ketoglutarate-linked hydroxylases undergoes a slow oxidation, as a result of a side-reaction of the enzyme. This results in inactivation of the enzyme, and the iron can only be reduced again, and activity be restored, by reaction with ascorbate (vitamin C). Because the oxidation of the iron is due to a side-reaction, the requirement for, and hence oxidation of, ascorbate does not show simple stoichiometry with the hydroxylation of substrate."
"In the iron-dependent ketoglutarate-linked hydroxylases (eg proline hydroxylase), ascorbate is not reduced stoichiometrically with hydroxylation of the substrate."
"T"
"The iron in iron-dependent ketoglutarate-linked hydroxylases undergoes a slow oxidation, as a result of a side-reaction of the enzyme. This results in inactivation of the enzyme, and the iron can only be reduced again, and activity be restored, by reaction with ascorbate (vitamin C). Because the oxidation of the iron is due to a side-reaction, the requirement for, and hence oxidation of, ascorbate does not show simple stoichiometry with the hydroxylation of substrate."
83, ascorbate.bmp
"In infection there is a decrease in the leukocyte saturation with vitamin C. This is because infection causes depletion of vitamin C."
"F"
"The decrease in leukocyte saturation with vitamin C in infection is because of the release into the circulation of granulocytes, which are saturated with vitamin C at a very much lower concentration than other leukocytes. Therefore the average leukocyte concentration of vitamin C falls, but only because the proportion of different types of leukocyte has changed."
"Ascorbic acid (vitamin C) turnover is increased in rats and mice given a variety of xenobiotics (foreign compounds). Therefore human beings need additional vitamin C when they are exposed to xenobiotics."
"F"
"The increase in ascorbate turnover occurs in animals for which ascorbate is not a vitamin, but an intermediate in the synthesis of glucuronic acid, which is used to conjugate many metabolites of xenobiotics for excretion. Since human beings cannot synthesize vitamin C from glucuronic acid, this is irrelevant to human nutrition."
-999
Copyright David A Bender 2002

