Dr David McGrath

Spine Physician

MB BS (Hons) FAFOM, RACP, FAFMM
Master of Pain Medicine

Vit A levels (retinol)
plasma>30 mg/dL
serum 45-65 mg/dL
Daily Dosage 1-3 mg
Toxic 6 mg /day (see vitamin interactions A,D,E,K)

Common Forms
1. Retinol (alcohol form)
2. Retinal (aldehyde form)
3. Retinoic Acid (acid form) Active Form
4. Carotene (alpha,beta)
5. Lycopene
6. Lutein
7. Zea/xanthin
8. Crypto/xanthin

Sources
1. Retinyl Esters (retinyl molecule + fatty acid molecule) (animal fats) Lipases,esterases from pancreas releases retinol
2. Carotenes (alpha,beta,gamma) (split to produce one of vitA forms) (red/yellow vegetable,fruit pigments) (also called carotenoids ) eg lycopene Carotenes often complexed with proteins. Pepsin in stomach creates hydrolysis
3. Egg yolk pigments (Zea and crypto xanthins )
4. Cod Liver Oil best source, also for VitD

Blood Transport
1. Chylomicrons transport from GIT
2. RBP binding protein. Complex (retinol-RBP-TTR-T4) (TTR=transthyretin=prealbumin )
3. Albumin transport

Hormone Action
1. Retinoic acid has nuclear reactions (nuclear receptors)
2. Morphogenesis. Lungs,skin,trachea,GIT. Essential normal cell differentiation.

Deficiency is a major cause of morbidity worldwide (rarely toxicity)
1. Stunted growth
2. Cataracts
3. Night vision
4. Immunodeficiency (susceptible to infections)
5. Bone excess growth. Bone,muscle pain
6. Xero/derma
7. Kerato/malacia
8. Xero/sis
9. Conjuncivitis,keratitis, episcleritis,(conjunctiva,sclera, cornea )(xero/phthalmia)
10. Dry, itchy, scaly skin,alopecia, hair coarsening,acne (oil,sweat,hair follicles,differentiation)
11. Ataxia

Retinyl esters/retinol play an important role in
1. Maintaining/synthesis glycoproteins, (lectins) important for cell-cell interaction

Retinol
1. Synthesis of light photo-pigment in eye (rods,cone cells) rhodopsin

Acne
13cis retinoic acid (acutane) teratogenic,

Interactions
1. Protein, zinc,iron
2. Vit K and E (excess reduces vit K absorption,lowers vitE)
3. Synergistic with vitD (vit D ptotective against vitA toxicity)

Metabolism
1.Irreversible step to retinoic acid
2.Bile excretion 70%, some kidney,lungs. (entero hepatic circulation loop)