Vitamin A (Retinol)
A fat-soluble vitamin, retinol (vitamin A) is found in milk, butter, eggs, liver and most fruit and vegetables. Very high levels are found in orange-coloured foods, for example: pumpkin, carrots, pawpaw, etc.
Vitamin A is essential for the normal function of the skin and eyes. It is vital for the formation of the pigment in the retina at the back of the eye, but there is no evidence that extra amounts can improve vision in people with sight problems or that it can cure skin problems.
The normal amount of vitamin A in blood is 0.7 to 2.8 µmol/L.
The recommended daily dietary intake is 425 µg in infants, 350 µg in children and 750 µg in adults.
In an entire lifetime, an intake of only 80 grams of vitamin A is required, provided the intake is evenly spread throughout life.
A vitamin A deficiency (hypovitaminosis A) may occur with starvation, tropical sprue, a poor or fad diet that lacks vitamin A, and alcoholism or narcotic addiction which may lead to the other causes. Symptoms include reduced night vision, dry eye surface, eye ulceration and dry skin. Permanent damage to the retina (light sensitive area at the back of the eye) is possible. Blood test measurements of low vitamin A levels are inaccurate, and the diagnosis must be made by history and clinical signs.
An excess of vitamin A (hypervitaminosis A) causes carotenaemia, which is characterised by yellow skin, palms and soles, and may be cause foetal abnormalities in pregnant women.