Fat Soluble Vitamins Flashcards
Vitamin A
What are the two forms of vitamin A
Preformed Vitamin A - active form in the body
* retinoids (retinal, retinal, retinoic acid)
* found in animal products
Provitamin A
* Carotenoids (beta-carotene, alpha carotene, lutein, lycopene, zeaxanthin, canthaxanthin)
* must be converted to retinoid form
* Found in plants
Vitamin A
Transport of Vitamin A
Transported via chylomicrons or VLDL to the liver
* Transported from the liver as retinol via retinol-binding protein (RBP) to target tissue
Vitamin A
Functions of Vitamin A
- Retinol is needed for reproduction (sperm production and foetal development)
- Retinoic acid supports growth and cell maturation, bone formation and gene expression
- Retinal is needed for night and colour vision
Retinol to Retinal -> Retinoic acid
Essential for vision, healthy epithelial tissues and growth
Vitamin A
The Visual Cycle - Cones
- responsible for vision under bright lights
- translate objects to colour vision
Vitamin A
The Visual Cycle - Rods
- Responsible for vision in dim lights
- Translates objects to black and white vision
- Contains a pigment – rhodopsin (protein opsin bound to retinal)
Vitamin A
Cell Health and Maintenance
- Epithelial cells line the outside (skin) and external passages (mucus forming cells) within the body
- Retinoic acid influences how epithelial cells differentiate and mature
- Without vitamin A, cells will deteriorate
- Leads to xerophthalmia (major cause of blindness) and follicular hyperkeratosis (skin disorder)
Vitamin A
Deficiency of Vitamin A
- Night blindness (inadequate cis-retinal)
- Decreased mucus production
- Bacterial invasion in the eye
Xerophthalmia:
Conjunctival xerosis (dryness) -> Bitot’s spots (plaque formation) -> Irreversible blindness
Vitamin A
Toxicity of Vitamin A - Chronic
- Bone/muscle pain, loss of appetite, skin disorders, headache, dry skin, hair loss, increased liver size, vomiting
- Increased activity of osteoclasts causes weakened bones and contributes to osteoporosis and fractures
Vitamin A
Toxicity of Vitamin A - Teratogenic (affects of foetal development)
Teratogenic (affects foetal development)
* Can produce physical defects on developing foetus e.g. spontaneous abortion, birth defects
Vitamin A
Hypercarotenaemia
- High amounts of carotenoids in the bloodstream turns skin a yellow-orange colour
- Excessive consumption of carrots/squash/betacarotene supplements
Vitamin A
Food Sources of Vitamin A
Preformed - retinoids
* Liver, fish oils, fortified milk, eggs
* Contributes to half of the average vitamin A intake
Proformed - Beta carotene and carotenoids
* Dark-green leafy vegetables, yellow-orange vegetables/fruits
Vitamin D
What are the two sources of Vitamin D
- Dietary
* Vitamin D2 from plants
* Vitamin D3 from animals - Endogenous
Vitamin D metabolism
7-dehydrocholesterol
Precursor (in the skin) that converts to vitamin D3
Vitamin D metabolism
Cholecalciferol
Vitamin D from sunlight trigger the converison of a cholesterol present on our skin > convets to cholecalciferol (D3) in blood
Vitamin D metabolism
Calcidiol
In our liver, an enzyme will hydroxylate the cholecalciferol molecule turning it into calcidiol
Vitamin D metabolism
Calcitriol
- is the active form of vitamin D
Calcidiol will be further activated in the kideny through hydroxylation = Calcitriol (active form of Vitamin D)
Vitamin D metabolism
PTH (parathyroid hormone)
When blood calcium and phosphate levels are low the
release of enzymes (1-α hydroxylase) will be released
* This stimulates the activation of Vitamin D
PTH (parathyroid hormone) will trigger the 1-α hydroxylase
- PTH also regulates calcium
- Love blood valcium = increases PTH = increases osteoclast activity
Osteoclasts: promote bone demineralisation
Vitamin D
Function of Vitamin D
Vitamin D is a hormone – a compound manufactured by one part of the body that causes another part to respond
* Resulting in the body producing the minerals needed for bone growth and maintenance
* Regulates synthesis of bone proteins (Vitamin K helps synthesise this protein)
Vitamin D
Vitamin D deficiency - Rickets
Rickets: Low vitamin D in children (requires both lack of exposure to sunlight and a poor diet)
* decreased calcification of growing ends of bones (epiphyses)
* Bones bow under pressure
* Seen in cystic fibrosis (fat malabsorption)
Vitamin D
Vitamin D deficiency - Osteomalacia
Osteomalacia: (soft bone) adult form of rickets
* Due to dietary vitamin D deficiency, lack of sunlight or to extensive liver or kidney damage
* Less obvious symptoms compared to children
Vitamin D
Vitamin D deficiency - osteoporosis
Osteoporosis = low bone density (higher risk of fracture)
Vitamin D deficiency is more prevalent among older adults for several factors:
* The skin, and kidney loses capacity to make and activate vitamin D
* Spend much of the day indoor
* Drink lesser milk (main dietary source of vitamin D)
Vitamin D
Vitamin D toxicity
- From excess supplementation (not from sun exposure)
Symptoms: - over-absorption of calcium (hypercalcaemia), increased calcium excretion
Vitamin D
Food sources of Vitamin D
Limited range of foods:
* Oily fish (salmon, herring)
* Egg yolks
* Liver
* Margarine in Australia is fortified
>80% of vitamin D in Australia/NZ comes from sun exposure
Vitamin E
Forms of Vitamin E
8 naturally occuring forms - includes tocopherols and tocotrienols
* most important form is a-tocopherol (alpha)
