vit C Flashcards
explain the history of vit C in 1500, 1535, 1757, 1804, 1928, 1933
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.
what can vit c be synthesised from
glucose or galactose in plants and most animals.
vit C is an intermediate in what and whatpathway
Intermediate in gulonolactone pathway of glucose metabolism.
vit C is required in species lacking what
L-gulonolactone oxidase.
give ex of some animals not able to synthesis vit C
Some monkeys, gunnie pigs, bats, fish
what are vitamers
different chemical compounds which show the same biological activity.
name some vitamers of vit C
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.
name the 3 different vit c interrelationship structures
ascorbate
monodehydroascorbate (semidehydroascorbate)
dehydroascorbate
Dehydroascorbate is fully oxidised form
what the storage organ of ascorabat in body
No storage organ for ascorbate, apart from leukocytes.
what is the body pool plateaus of vit C in body
at ~20 mg/kg body weight
what tissues in body have significant concs of vit C
adrenal and pituitary glands.
Pituitary gland sits at back of nose in brain
Adrenal gland sits on top of kidneys
describe the percentage of ascorbate in the blood
70% in plasma and erythrocytes.
30% in white cells (10% in leukocytes).
functions of vit C
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
explain vit C as an antioxidant
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
explain collagen synthesis
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+.
describe relationship between vit C and cancer prevention
Can inhibit conversion of nitrites to nitrosamines (carcinogenic) in stomach
can vit C reduce risk of cardiovascular disease
yes
describe relationship of vit C and prevention and treatment of common cold
Does not prevent infection
Slight decrease in duration and severity of symptoms
explain metabolism in rats and hamsters
passive intestinal absorption of vit c.
explain metabolism in Guinea pigs and humans
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.
explain the requirements of vit c to prevent scurvy, and for wound healing
Amount needed to prevent and cure scurvy: ~10 mg/d.
Wound healing: 20 mg/d.
what value does Plasma conc stabilise of vit c
around 70-85 µmol/l (70-100 mg/d).
leucocyte saturation values
100-200 mg/d.
what is the Amount above which everything ingested is excreted for vit c
~200 mg/d.
whats the value Requirements set by determining size of body pool and fractional rate of loss
45-60 mg/d.
what are the uk RNIs, LRNIs, and EARs for ages 19-50 years
UK: RNI = 40mg, LRNI = 10mg, EAR = 25mg
what is the DRV for EU and Australasia
45mg,
what is the EU RDA for labelling
60mg
whats the DRV for US/canada
75 mg (females) 90mg (males)
what are reasons for an increased requirement in vit C
Smokers - may be almost twice that of non-smokers
Post-surgery
Acute and chronic infection
sources of vit c
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
what percentage of the UK diet come from each food group
Vegetables + potatoes, 37%
Non-alcoholic beverages, 22%
Fruit, 19%
Other, 22%
give some veg sources that are high in vit C
brussel sprouts, peppers, broccoli, and peas
give some fruit sources that are high in vit c
blackcurrants, kiwi fruit, strawberries, oranges, orange juice, mangos, raspberries
what causes loss in vit c in fruits and veg
prep, and distribution
as seen in old persons home in holland where 90- 50% of vit c in fruit /veg were lost from processing
can vit C be lost during chilled storage
yes,
vit c is lost every day during chilled storage
what unexpected reheating processes loose vit c in food
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
how long can it take for symptoms of clinical deficiency to be seen
3-6 months
what are the symptoms of scurvy from vit c deficiency
- 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
what are infantile signs of scurvy (6-12 months)
- Subperiosteal haemorrhages under skin
- Tiny fractures in bones
- Abnormal cartilage – Affecting joints
- Adopts frog position – where arms and legs are wide open
how can we measure the nutritional status of vit c in the body
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
