vit C

Question 1

explain the history of vit C in 1500, 1535, 1757, 1804, 1928, 1933

Answer 1

1500BC: Scurvy described in the Ebers papyrus

1535: Cartier’s Quebec expedition - Local native Americans advised drinking a brew from the bark and leaves of a local tree (white cedar) to prevent and cure scurvy.

1757: James Lind showed that oranges and lemons protective.

1804: British Navy daily rations of lemon or lime juice.

1928: Szent-Gyorgyi isolated a crystalline substance (ascorbic acid) from orange juice, cabbage juice and adrenal glands.

1933: Structure established by Haworth et al.

Question 2

what can vit c be synthesised from

Answer 2

glucose or galactose in plants and most animals.

Question 3

vit C is an intermediate in what and whatpathway

Answer 3

Intermediate in gulonolactone pathway of glucose metabolism.

Question 4

vit C is required in species lacking what

Answer 4

L-gulonolactone oxidase.

Question 5

give ex of some animals not able to synthesis vit C

Answer 5

Some monkeys, gunnie pigs, bats, fish

Question 6

what are vitamers

Answer 6

different chemical compounds which show the same biological activity.

Question 7

name some vitamers of vit C

Answer 7

L-ascorbic acid and the oxidised forms

Monodehydroascorbate

Dehydroascorbic acid

Also D-iso-ascorbic acid (erythorbic acid)

Sodium + calcium salts of ascorbate used in food processing

Diketogulonic acid – a further oxidation product with no biological activity.

Question 8

name the 3 different vit c interrelationship structures

Answer 8

ascorbate
monodehydroascorbate (semidehydroascorbate)
dehydroascorbate

Dehydroascorbate is fully oxidised form

Question 9

what the storage organ of ascorabat in body

Answer 9

No storage organ for ascorbate, apart from leukocytes.

Question 10

what is the body pool plateaus of vit C in body

Answer 10

at ~20 mg/kg body weight

Question 11

what tissues in body have significant concs of vit C

Answer 11

adrenal and pituitary glands.

Pituitary gland sits at back of nose in brain
Adrenal gland sits on top of kidneys

Question 12

describe the percentage of ascorbate in the blood

Answer 12

70% in plasma and erythrocytes.
30% in white cells (10% in leukocytes).

Question 13

functions of vit C

Answer 13

Hydroxylation of proline + lysine for collagen synthesis

Conversion of dopamine to noradrenaline (norepinephrine)

Conversion of lysine to carnitine (needed for transfer of LCFA (long chain fatty acids) into mitochondria)

Required by enzyme needed to activate various peptide hormones and hormone releasing factors

Catabolism of tyrosine to carbon and water

Antioxidant – as relationship with vit E

Enhances absorption of non-haem iron

Question 14

explain vit C as an antioxidant

Answer 14

Antioxidant systems help eliminate free radicals and reduce oxidative stress.

Regenerates vitamin E from its radical state.

vit C can donate an electron to neutralize a free radical.
the available electron of a free radical can oxidise (and damage) important biological molecules like DNA

Question 15

explain collagen synthesis

Answer 15

Collagen is a connective tissue protein.

Vitamin C is essential for hydroxylation of proline + lysine residues in collagen (enables crosslinking of collagen molecules, increasing strength + elasticity of connective tissue).

Proline —-prolylhydroxlase—> hydroxyproline
Lysine —–lysylhydroxylase—-> hydroxylysine

Vit C needed to convert Fe3+ on enzymes back to Fe2+.

Question 16

describe relationship between vit C and cancer prevention

Answer 16

Can inhibit conversion of nitrites to nitrosamines (carcinogenic) in stomach

Question 17

can vit C reduce risk of cardiovascular disease

Answer 17

yes

Question 18

describe relationship of vit C and prevention and treatment of common cold

Answer 18

Does not prevent infection

Slight decrease in duration and severity of symptoms

Question 19

explain metabolism in rats and hamsters

Answer 19

passive intestinal absorption of vit c.

Question 20

explain metabolism in Guinea pigs and humans

Answer 20

Na dependent active transport at intestinal mucosa brush border membrane.

70-95% (this is efficient) of vit C is absorbed at intakes of 30-200 mg/d.(normal intakes)

Absorption decreases to 20% with 5 g dose ingested.

Bioavailability similar between foods and supplements.

At plasma concs >70-85 µmol/l – renal transport system saturated and vitamin excreted in urine.

Much of ascorbic acid excreted in urine unchanged or as dehydroascorbate or diketogulonate.

Question 21

explain the requirements of vit c to prevent scurvy, and for wound healing

Answer 21

Amount needed to prevent and cure scurvy: ~10 mg/d.

Wound healing: 20 mg/d.

Question 22

what value does Plasma conc stabilise of vit c

Answer 22

around 70-85 µmol/l (70-100 mg/d).

Question 23

leucocyte saturation values

Answer 23

100-200 mg/d.

Question 24

what is the Amount above which everything ingested is excreted for vit c

Answer 24

~200 mg/d.

Question 25

whats the value Requirements set by determining size of body pool and fractional rate of loss

Answer 25

45-60 mg/d.

Question 26

what are the uk RNIs, LRNIs, and EARs for ages 19-50 years

Answer 26

UK: RNI = 40mg, LRNI = 10mg, EAR = 25mg

Question 27

what is the DRV for EU and Australasia

Answer 27

45mg,

Question 28

what is the EU RDA for labelling

Answer 28

60mg

Question 29

whats the DRV for US/canada

Answer 29

75 mg (females) 90mg (males)

Question 30

what are reasons for an increased requirement in vit C

Answer 30

Smokers - may be almost twice that of non-smokers Post-surgery Acute and chronic infection

Question 31

sources of vit c

Answer 31

Fresh vegetables and fruit, particularly spinach, tomatoes, broccoli, strawberries, citrus fruits. Potatoes contain <20 mg/100g (<8 mg/100g after storage) but can be a significant source. Bruising, damage, cutting, processing, storage and cooking lead to loss of vitamin. Warm holding leads to loss Most fruits have decent source of vit c Potatoes lose significant amount of vit c after storage, but still are a significant source

Question 32

what percentage of the UK diet come from each food group

Answer 32

Vegetables + potatoes, 37% Non-alcoholic beverages, 22% Fruit, 19% Other, 22%

Question 33

give some veg sources that are high in vit C

Answer 33

brussel sprouts, peppers, broccoli, and peas

Question 34

give some fruit sources that are high in vit c

Answer 34

blackcurrants, kiwi fruit, strawberries, oranges, orange juice, mangos, raspberries

Question 35

what causes loss in vit c in fruits and veg

Answer 35

prep, and distribution as seen in old persons home in holland where 90- 50% of vit c in fruit /veg were lost from processing

Question 36

can vit C be lost during chilled storage

Answer 36

yes, vit c is lost every day during chilled storage

Question 37

what unexpected reheating processes loose vit c in food

Answer 37

microwaving - theses still significant vit c loses in food similar to if cooked in water as its water soluble also oven reheating loses vit c levels in foods

Question 38

how long can it take for symptoms of clinical deficiency to be seen

Answer 38

3-6 months

Question 39

what are the symptoms of scurvy from vit c deficiency

Answer 39

- Weakness - Fatigue - Skin changes- becoming thin - Inflamed and bleeding and receding gums, so teeth fall out - Impaired wound healing. So infection This seen in sea men before their ration daily of lemon and lime juice

Question 40

what are infantile signs of scurvy (6-12 months)

Answer 40

- Subperiosteal haemorrhages under skin - Tiny fractures in bones - Abnormal cartilage – Affecting joints - Adopts frog position – where arms and legs are wide open

Question 41

how can we measure the nutritional status of vit c in the body

Answer 41

Vitamin C is not stored for long in the body. Serum and leukocyte concentrations: most common for measuring the status Urinary excretion: limited use – recent intake