Vitamin A – Explored
Regulation of Growth and Differentiation of all Cells
Immune Function & Regulation
There are 3 forms of Vitamin A within the body:
MAKE AN OVERVIEW OF THESE FORM – FLOW CHART ETC
Retinol – preformed animal form
Retinaldehyde (Retinal) – converted by the body from Retinol.
Retinal is oxidised to make Retinoic Acid – the form of Vitamin A known to regulate gene transcription
Also add Beta-Carotene section
Vitamin A diffuses in the gut into micelles which enter the enterocytes. Enterocytes package these fats into Chylomicrons which carry the Vitamin A molecule into the blood via lymphatic capillaries (lacteals).
How it is converted from plant Beta Carotene to Retinol
Transporter / Carrier Proteins
Plasma Retinol Binding Protein
Transport & Storage:
Retinyl Esters are hydrolysed to generate All-Trans-Retinol, which binds to Retinol Binding Protein (RBP) before being released in the bloodstream.
All-Trans-Retinol/RBP complex circulates bound to the protein, Transthyretin.
Vitamin A as Retinyl Esters in Chylomicrons was also found to have an appreciable role in delivering Vitamin A to extrahepatic tissues, especially in early life.
Fat soluble Vitamin A in the form of Retinyl Esters is stored in the liver.
Dairy products, fortified cereal, liver, and fish oils.
Orange and green vegetables, such as sweet potato and spinach.
700 μg RAE women
900 μg RAE men
The RDA is the recommended intake needed by nearly all of the population to ensure adequate hepatic stores of vitamin A in the body (20 μg/g for four months if the person consumes a vitamin A-deficient diet) to support normal reproductive function, immune function, gene expression, and vision
Tolerable upper intake: tolerable upper intake level (UL) for vitamin A in adults is set at 3,000 μg RAE/day.
Over 3000ug RAE (10000 IU) – Preformed animal VITA only
Deficiency Signs and Symptoms
Increased susceptibility to infections
(Even children who are only mildly deficient in vitamin A have a higher incidence of respiratory complications and diarrhoea, as well as a higher rate of mortality from measles infection compared to children consuming sufficient vitamin A).
Thyroid and Skin disorders
Disease of the eye and blindness
Impaired dark adaptation known as night blindness or Nyctalopia
Abnormal changes in the conjunctiva (corner of the eye), manifested by the presence of Bitot’s spots.
Severe or prolonged vitamin A deficiency eventually results in a condition called Xerophthalmia (Greek for dry eye), characterised by changes in the cells of the cornea (the clear covering of the eye) that ultimately result in corneal ulcers, scarring, and blindness.
Immediate administration of 200,000 international units (IU) of vitamin A for two consecutive days is required to prevent blinding Xerophthalmia.
Toxicity Signs and Symptoms
Deficient kids infected with measles while malnourished, immunodeficient, or are at risk of measles complications.
Acute Promyelocytic Leukaemia
Various skin diseases
Vitamin A Serum Levels
Sub-clinical vitamin A deficiency is often defined by serum retinol concentrations lower than 0.70 μmol/L (20 μg/dL). In severe vitamin A deficiency, vitamin A body stores are depleted and serum retinol concentrations fall below 0.35 μmol/L (10 μg/dL).
World Health Organization considers vitamin A deficiency a public health problem when the prevalence of low serum retinol (<0.70 μmol/L) reaches 15% or more of a defined population