What is vitamin A?
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:
What is vitamin A deficiency?
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.
What causes vitamin A deficiency?
- Primary vitamin A deficiency is caused by prolonged dietary deprivation.
- Secondary vitamin A deficiency is caused by reduced absorption, storage or transport of vitamin A.
Who gets vitamin A deficiency?
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:
- Coeliac disease
- Cirrhosis of the liver
- Pancreatic insufficiency
- Bile duct disorder
- Duodenal bypass
What are the signs and symptoms of vitamin A deficiency?
Vitamin A deficiency is the leading cause of preventable blindness in children worldwide.
- Impaired dark adaptation (night blindness) due to lack of the photoreceptor pigment rhodopsin.
- Xerophthalmia: dry, thickened conjunctiva and cornea
- Bitot spots: keratinized growths (metaplasia) on the conjunctivae causing hazy vision
- Keratomalacia: corneal erosions and ulceration
Vitamin A deficiency can also be recognised by its keratinising effect on the skin and mucous membranes.
- Dry, scaly, thickened skin with prominent follicular scale
- Dry lips and thickened tongue
- Keratinisation of the urinary, gastrointestinal and respiratory tracts
Other symptoms and signs
- Impaired immunity leading to gastrointestinal and respiratory tract infections
- Growth retardation in children
How is vitamin A deficiency diagnosed?
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.
How is vitamin A deficiency treated and prevented?
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:
- 50,000 IU for infants below 6 months of age
- 100,000 IU for infants 6–12 months of age
- 200,000 IU for 12 months through adulthood
Vitamin A deficiency can be prevented through a diet which includes:
- Spinach, kale, collards, brocolli and other leafy green vegetables
- Beta-carotene-rich fruits such as apricots or peaches, and highly-coloured vegetables such as carrots, squash, sweet potato
- Milk or cereals that have been fortified with vitamin A
- Egg yolks
- Fish liver oils
In developing countries, successful preventative measures include:
- Encouraging breastfeeding
- Periodic administration of high-dose vitamin A for children
- Encouraging families to grow fruits and vegetables for food supplementation