Vitamins Flashcards
What are Vitamins?
A complex organic substance required in the diet in small amounts , compared to other dietary components such as protein carbohydrate and fat, and whose absence leads to a deficiency disease.
How are vitamins divided?
- Water soluble: B group, C
- Fat soluble: A D E K
What are the diffrences between water soluble and fat soluble?
-
Water soluble: B group, C
* not stored extensively - needed regularly in diet
* needed regularly
* generally not toxic in excess (within reason) -
Fat soluble: A D E K
stored
* not absorbed easily
* not excreted easily
* may be toxic in excess (A, D)
Sources of Vitamin C?
Citrus fruits, tomatoes, berries
function of vitamin c?
- An anti-oxidant nutrient
- Hydroxylation of proline and lysine in collagen formation.
needed to maintain the Fe(II) necessary for proline and lysine
hydroxylase activity in the reduced, active state. - Reduction of dietary Fe in the stomach for absorption
- Possibly, in vivo, as an anti-oxidant protecting vitamins A, E, K from oxidation
What is the vitamin C defieciency?
When does this present?
Scurvy
* The well fed human body has a 6 month store of vitamin C
* Signs of scurvy after three months on vitamin C free diet.
* impaired wound healing, haemorrhages and anaemia (also
from decreased Fe and folate absorption).
Presentation of scurvy?
- impaired wound healing, haemorrhages and anaemia (also
from decreased Fe and folate absorption).
Vitamin C status in the uk?
- Low status in the elderly, in alcoholics and in adolescents
especially on ‘junk’ food. - Smokers need twice the normal intakes (80 mg/day) as the
turnover of ascorbic acid is greatly increased by smoking.
Viatmin A Consequences of megadoses?
Benefits uncertain and under review
* cholesterol turnover, immune function, male fertility, cancer prevention, Se and Fe utilisation, physical working capacity
- Supplements may ease symptoms
- Commen cold: No evidence that megadoses have an effect
- Heart disease, cancer, eye diseases - no clear pattern
Risks of megadoses of vitamin C?
- Oxalate (major metabolite)) kidney stones in susceptible individuals
- diarrhoea
- systemic conditioning- Pregnant women on high doses may have infants with unusually high requirements and individuals on high intakes are at risk of deficiency if the intake is lowered to levels which are adequate for most people.
Causes of fat soluble vitamin deficiency?
Causes of deficiency
Primary:
- dietary deficiency
- low fat diet
- (usually by choice in developed societies)
- fat malabsobtion absorption
Sources of Vitamin A?
Sources
- as retinol
- Animal liver and fish liver oils, whole milk and egg yolk
- plant carotenoids (mainly b- carotene)
- Green/yellow/ orange vegetables and fruit.
Absorption of Vitamin A sources?
Absorption
diffrerents between plant and aminal sources
- Carotenoids (plant sources) are cleaved to 2 retinol molecules
- conversion is inefficient,
- ratio carotene : retinol not 1:2 but 6:1
- Potency is expressed as retinol equivalents
1 RE = 1 ug retinol
Active forms of Vitamin A
Active forms
* retinoic acid - acts as a hormone
* retinal - in vision
* (b - carotene - antioxidant)
What are two main functions of vitamin A?
- control of protein synthesis
- in vision
How does Vitamin A control protein synthesis?
- retinoic acid binds specific receptor protein in cytosol, then
- binds chromatin and affects synthesis of proteins involved in cell growth and differentiation.
- acts in a similar way to steroid hormones
How is Vitamin A used in vision?
- best understood function
- at low light intensity (scotopic vision) 11-cis retinal participates in conversion of light energy to impulses in the optic nerve in the rod cells of the retina
Transport and Storage of Vitamin A?
- From the gut to the liver in chylomicrons
- From the liver to the tissues bound to a specific retinol binding protein, and pre-albumin.
Where is Vitamin A presented?
- rarely seen in developed countries, but common in developing
countries e.g. India & SE Asia - Usually associated with inadequate protein diets.
What does Vitamin A deficiency affect?
- Affects synthesis of retinol binding protein and therefore transport to the tissues.
Administration of vitamin A alone often does not help. -
Night blindness(role in vision), followed by: progressive keratinisation of the cornea (xerophthalmia), and finally keratomalacia and irreversible blindness. - progresses without treatment
The development of xerophthalmia and keratomalacia
relates to its role in the function of epithelial cells and
mucopolysaccharide synthesis.
Vitamin A requirements
- In pregnancy no more than 3.3mg/day are recommended
- RNI is 0.7 mg/day for men and 0.6mg/day for women
UK animal livers: 13 - 40 mg/100g
- Pregnant women should not take supplements or eat liver regularly - can lead to birth defects
If too much Vitamin A is taken? What happens?
Toxicity
*Dermatitis, hair loss, mucous membrane defects, hepatic dysfunction, thinning and fracture of long bones.
Unlikely with normal sources but possible with supplements e.g. for acne or colds.
Sources of vitamin E?
Source
* Associated with beauty and fertility
* Vegetable oils especially wheat germ oil, nuts, green
vegetables.
Bad sources of Vitamin E
- Canned and frozen foods severely depleted
- includes family of tocopherols
What is Vitamin E?
What is a safe level for Vitamin E?
includes family of tocopherols
most potent: a-tocopherol –
naturally occurring ANTIOXIDANT
Safe level - up to 1 g/day
Function of vitamin E?
- Prevents oxidation of unsaturated/poly-unsaturated fatty acids (PUFA) in cell membranes and circulating lipoproteins
* PUFA are particularly susceptible to attack by free radicals (generated in body) - Destruction disrupts membrane structure and cell integrity.
- Some polyunsaturated fatty acids are precursors of prostaglandins and so prostaglandins metabolism is also disturbed.
How does Free radical scavenging occur with vitamin E?
- Polyunsaturated fatty acids are susceptible to attack by free
radicals
other radicals are generated in this process. - Reaction of a fatty acid radical with oxygen gives a peroxyl radical.
- This continues chain reaction by attacking other PUFAs
- it can react with an anti-oxidant – e.g vitamin E - thus
terminating the chain reaction
itamin E can be regenrated
Why is Vitamin E a radical?
vitamin E becomes a radical itself,
* stable
* can be reduced to original form by other antioxidant nutrients,
possibly ascorbic acid.
What does Vitamin E deficiency cause?
Deficiency
* Known in animals as a cause of sterility and muscular dystrophy.
Who does Vitamin E deficincey occur in and why?
- Virtually unknown except in premature, low birth
weight infants. vitamin E does not cross the placenta
easily; - human milk is not a good source of vitamin E.
- Haemolytic anaemia due to fragility of red cell
membranes is characteristic. - Vitamin E is now included in infant formulae
Proposed benefits in vitamin E?
- Requirements difficult to establish, likely to be higher with high PUFA intake.
- A protective effect against cardiovascular disease and cancer?
- Vitamin E is thought to protect fatty acids and apoprotein B in LDL from oxidative damage.
- evidence that damaged LDL in arterial wall is part of mechanism that leads to atherosclerotic damage.
- Studies inconclusive
- Cancer? May reduce risk in men but not in women.
What is Vitamin D?
- a group of similar compounds.
*Cholecalciferol (vitamin D3) - occurs naturally in animals.
*functions by binding to intra-cellular receptors that eventually interact with DNA –
*i.e. acts like most steroid hormones.
Vitamin as it needed in diet but can still be synthesised
What is Vitamin D2?
Vitamin D2 (ergocalciferol)
* derived from ergosterol widely found in plants, fungi and moulds.
* important pharmaceutically and commercially as a food additive because of ready availability of ergosterol.
Sources of D2?
Sources:
* Milk and dairy products, fortified margarine, eggs.
* Cholecalciferol formed in skin by UV light on 7- dehydrocholesterol,
* ergocalciferol is formed from ergosterol by the action
of UV light, prepared commercially
Function of vitamin D?
- Acts to maintain correct levels of calcium and phosphate in the blood so that proper mineralisation of bone is achieved.
- Biggest influence on calcuim and phosphate absoption
Vitamin D Deficiency?
- Rickets in children and osteomalacia in adults