Introduction - vitamin A
Introduction - vitamin A deficiency
Causes
Demographics
Signs and symptoms
Diagnosis
Treatment and prevention
Vitamin A is a fat soluble organic compound required for vision and for epithelial tissue health. It is converted in the body from dietary beta-carotene and 3 other carotenoids. 80-90% of vitamin A is stored in liver.
Vitamin A is also called retinol. Natural and synthetic compounds derived from retinol are known as retinoids and include:
Newer synthetic compounds that act through the retinoid pathway include tazarotene, bexarotene and adapalene.
The normal range of vitamin A/retinol is 28–86 μg/dL. Vitamin A deficiency is defined as serum retinol levels of below 28 μg/dL. Vitamin A deficiency can lead to blindness, skin disease and growth retardation in children.
Vitamin A deficiency is prevalent in Africa and Southeast Asia, where it is estimated that 250 million preschoolers suffer from this deficiency due to lack of carotenoids in their diet. Symptoms are aggravated by serious infection, particularly measles.
Vitamin A deficiency can also occur in adults with diseases of the gastrointestinal system that interfere with absorption of vitamin A. These include:
Vitamin A deficiency is the leading cause of preventable blindness in children worldwide.
Vitamin A deficiency can also be recognised by its keratinising effect on the skin and mucous membranes.
Diagnosis of vitamin A deficiency is usually clinical. The history of impairment of dark adaptation is very suggestive of vitamin A deficiency, but can also occur with therapeutic use of retinoids (eg isotretinoin prescribed for acne). The finding of xerophthalmia and dry skin is suggestive of vitamin A deficiency, but can be due to other causes.
Measurement of serum vitamin A/retinol is useful if levels are under 28 μg/dL but the result may be normal if deficiency is mild. Low retinol levels are indicative of advanced disease, since the circulating levels of vitamin A do not drop until hepatic vitamin A supplies are depleted.
Diagnosis is confirmed by therapeutic response to vitamin A supplementation.
Vitamin A deficiency is treated with vitamin A palmitate oil at a dosage of 60,000 IU orally for 2 days, then 4,500 IU orally per day.
An alternative dosing is:
Vitamin A deficiency can be prevented through a diet which includes:
In developing countries, successful preventative measures include:
