what was the first Vit discovered
Vit A
Vit a is a generic term for a large number of……
….related compounds with Vit A activity
called retinoide
what is an early sign of Vit A deficiency
night blindness…lack of Vit A in back of eye
what are the 3 key forms of retinoids
- retinal (vision)
- retinol (transport; converted to other forms)
- retinoic acid (hormone)
Vit A interconversions
Vit A is esterified to FA in food
Carotenoids
plant derived
carotenoid blood concentrations can be used as biomarkers for fruit and veg intake
higher blood levels associated with lower risk of several chronic diseases
some have PROVit A activity
Beta carotene is most potent….
- potential to cleave TWO molecules of Vit A
- less efficient absorption than vit A
- less bioavailable
which carotenoids have pro Vit An activity
alpha carotene
beta carotene
beta cryptoxanthin
can carotenoids be converted to retinAL?
yes
Vit A and Carotenoid good
Vit A (retinoids)
- animal foods
- liver, fish, milk products, butter, egg yolk
Carotenoids
- plant foods
- orange and yellow fruits and veggies
- dark green leafy vegetables
Vit A bioavailability
the rate and extent at which a vitamin is absorbed and utilized
depends on amount in food and amount absorbed
animal sources (retinoids) are more bioavailable
RAE= retinol activity equivalents
vit A has best bioavailbility (all-trans-retinol)/aniaml source
then dietary beta carotene
then supplemental beta carotene
then other active carotenoids
metabolic functions of Vit A
VISION
- retinAL
- participates in visual cycle
- initiated by light, end result is AP
REGULATION OF GENE EXPRESSION
- retinOIC ACID
- repro, growth, integrity of imune system, integrity of epithelial cells
Vit A-regulation of gene expression
retinoic acid can act as a steroid hormone
retinoic acid actually binds to the DNA and alter protein
most physiological effects of Vit A result from its role in regulating gene expression
process of vit A in gene expression
1) retinol travels to target cell membrane
2) retinol–>retinal –>retinoic acid
3) retinoic acid travels intracellularly to the nucleus by CRABP (cellular retinoic acid binding protein)
4) retinoic acid attaches to DNA receptors and alters transcription
regulation of gene expresion and Vit A WRT repro, growth, immunity and other epithelial cells
REPRO
supports sperm development
support normal fetal development
GROWTH
role in bone turnover
RA regulates the gene expression of growth hormone
IMMUNITY
- maintains integrity of skin and mucosal cells
- differentiation of white blood cells
- “anti-infective” hormone
OTHER EPITHELIAL CELLS
- role in differentiation
- lungs, cornea, GI tract, skin
- Vit A also contribute toward RBC formation
**Vit A nutrient interactions
ZINC**
- Vit A need zinc
- Zn deficiency interferes with Vit A
- Zn needed for synthesis of RBP
- Zn needed for release of Vit A from liver storage
- Zn needed for conversion of retinOL to retinAL
IRON
-Vit A helps Iron
Combination of Vit A and iron reduces anemia more effectively than iron alone
-may relate to Vit A’s role in diffferentiation of RBD…hemoglobin
Vit A deficiency can lead to irreversible blindness
-xerophthalmia
lack of Vit A in FRONT of eye (cornea)
-ulcerations of the cornea
-leading cause of blindness in developing countries
what is the leading cause of blindness in developed countries?
diabetes
other effecets of Vit A deficiency
- decreased growth
- failure to reproduce
- increased susceptibility to infection
- keratinization of epithelial tissues
- cells change shape and secrete keratin
Vit A toxicity
can be toxic due to liver storage
-hypervitaminosis A
overconsumption of Vit A, NOT carotenoids
-Teratogenic risk
risk of birth defects if too much Vit A during pregnancy
harmful toxicity is due to Vit A not carotenoids
