Functions

Regulation of Growth and Differentiation of all Cells

Reproduction

Eye Development

Vision

Immune Function & Regulation

Forms

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

Absorption

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).

Conversion

How it is converted from plant Beta Carotene to Retinol

Transporter / Carrier Proteins

Plasma Retinol Binding Protein

All-Trans-Retinol/RBP complex

Transthyretin

NEEDS UPDATING

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.

Cell Receptor:

STRA6

Food Sources

Animal:

Dairy products, fortified cereal, liver, and fish oils.

Plant:

Orange and green vegetables, such as sweet potato and spinach.

RDA Dose

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

Supplemental Range:

Tolerable upper intake: tolerable upper intake level (UL) for vitamin A in adults is set at 3,000 μg RAE/day.

Toxicity

Over 3000ug RAE (10000 IU) – Preformed animal VITA only

Deficiency Signs and Symptoms

Blindness

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

Therapeutic Uses:

Deficiency

Deficient kids infected with measles while malnourished, immunodeficient, or are at risk of measles complications.

Acute Promyelocytic Leukaemia

Various skin diseases

Nutrient Interactions:

Drug Interactions:

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

http://lpi.oregonstate.edu/mic/vitamins/vitamin-A

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4584289/