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