Week 2 - Fat Soluble Vitamins Flashcards
Fat Soluble Vitamins
Fat soluble vitamins (4)
- Vitamin A
- Vitamin D
- Vitamin K
- Vitamin E
Names for Vit A
Retinol, Retinal and Retinoic acid
Sources of Vit A
Liver, cod liver oil, milk fats
Sources of B-carotene
yellow/orange fruit and veg + GLV
Functions of Vit A
Assist vision in dim light, maintenance of epithelial cells, normal bone formation
Recommended intake of Vit A
- Men (all ages)
- EAR 625ug/day
- RDI 900ug/day
- SDT 1500ug/day
- Women (all ages)
- EAR 500ug/day
- RDI 700ug/day
- SDT 1220ug/day
Absorption of Vit A
- Retinyl esters are broken down into proteins, fatty acids
- Retinol, carotenoid and lipids incorporated into micelles then passively absorbed into the small intestines
- Retinol then bound to Cellular Retinol- Binding Protein (CRBP) and are re-esterified by Lecithin Retinol Acyl Transferase (LRAT) into retinyl esters
- Incorporated into chylomicrons fro transport
Major storage form of retinol
Retinyl palmitate
Where is Vit A stored
- 80% in the liver
- Adipose tisse
- Lungs
- Kidneys
Three main functions of Vit A
-Vision – maintain surface epithelium, night vision
- Reproduction – deficiency can cause male infertility and low conception rates in females, including stillbirths
- Cell differentiation - gene expression, embryogenesis, immunity, growth, haemopoiesis (formation of blood cells)
Role of Vit A in vision
- Vitamin A is part of a molecule called 11-cis-retinal, which attaches to proteins in the eye called opsins (rhodopsin in rods and iodopsin in cones).
- When light hits the eye, 11-cis-retinal changes shape to become all-trans-retinal.
- This change causes the all-trans-retinal to detach from its opsin, a process called bleaching.
- The change triggers a nerve signal that travels to the brain, allowing us to see.
- After bleaching, all-trans-retinal is converted back to 11-cis-retinal through several steps.
- The 11-cis-retinal then reattaches to opsin, reforming rhodopsin and getting the visual system ready for more light.
- If there’s not enough vitamin A, 11-cis-retinal can’t be made properly, affecting rhodopsin formation and leading to night blindness.
Vit A deficiency - protein
Retinol binding protein which transports retinol around the body is dependant on protein intake
Vit A deficiency - mucopolysaccharide synthesis
- Reduced wettability of the eye surface
- Reduced tear production contributing to xerosis (dry and rough) of eye surface
- Reduced mucous production by mucous membranes with risk of infection
- Reduced taste
- Changes in skin - follicular keratitis
- Defective formation of bone, cartilage and teeth during growth
Vit A deficiency - Xerophthalmia
Clinical indicator early Vit A def is Bitot’s spots (foamy deposits on surface of conjunctiva)
Vit A deficiency biomarkers
Plasma Retinol concentration influenced by age, female sex hormones and inflammation
Signs of vitamin A toxicity
- High serum Vit A
- Bone pain and fragility
- Hydrocephalus (water on the brain) and vomiting (in infants and children)
- Dry fissured skin
- Brittle nails
- Hair loss (alopecia)
- Gingivitis (gum disease)
- Cheilosis (cracked corners of mouth)
- Anorexia
- Irritability
- Fatigue
β Carotene
β Carotene is converted to retinol in the body
An excess of carotene is carotenaemia - no health consequences
Names for Vitamin D
Cholecalciferol (D3) and Ergocalciferol (D2)
Sources of Vit D
- Cod liver oil
- Fatty fish, fortified margarine
- Egg yolk, butter, cheese, milk
Functions of Vit D
Aids absorption of calcium and phosphorus, maintaining bone formation, gene expression and modulation
Vit D deficiency
- Kids - rickets
- Adults - osteomalacia
