Vitamin A is an essential vitamin required by body for various purposes. It is often mentioned as an eye vitamin because deficiency of this vitamin may majorly affect eyesight. Vitamin A is not available in body; it has to be consumed through dietary source. This fat soluble vitamin is available in two forms, retinol and carotene. Retinol is found only in foods of animal origin. It is found in fish oils, liver, egg, butter, etc.
Carotene is a provitamin. Provitamins are substances which occur in food, which are not themselves vitamins but are capable of getting converted into vitamins while digestion of food. Carrots, green leafy vegetables, spinach, broccoli, pumpkin contain Beta carotene, which gets converted to retinol or vitamin A. Beta carotene is largely absorbed and converted into retinol in small intestine. The absorption of both retinol and Beta carotene is facilitated by fats and bile salts.
The clinical deficiency of vitamin A is rare in affluent countries. A dietary deficiency is only produced when there is insufficient supply of dairy produce, fish and vegetables. Vitamin A deficiency is largely present in developing countries due to malnutrition. It is prevalent in under developed countries of Asia, South America, and Africa and it may lead to very serious health consequences.
Deficiency Of Vitamin A (Retinol) And Eye Problems
Deficiency of vitamin A results in changes in epithelial surface of all parts of body. It may affect skin, intestine and even eyes. The tear glands of eye become dry and they are blocked with horny plugs of keratin, which decreases the secretion. This may result in irritation, inflammation and dryness in the eye surface.
Where vitamin A is deficiency is prevalent, minor disorders of eye and skin often recover more rapidly in children receiving regular prophylactic doses if the vitamin. It also improves the growth and well being. Below are some of the eye problems encountered with vitamin A or retinol deficiency.
- Night blindness: Night blindness or reduced vision at night is one of the earliest symptoms noted in vitamin A deficiency. Retinol is an essential component of a pigment present in eye. It is called rhodopsin. The vision in dim light depends on rhodopsin. Hence lack of vitamin A (retinol) may result in impairment of dark adaptation.
- Xeropthalmia: Vitamin A deficiency in moderate amount may cause dryness in conjunctiva. It becomes thick and pigmented. The pigments give a peculiar smoky white appearance which is called bitot’s spot. Xerosis or dryness and bitot’s spot occurs especially in children whose diet is deficient in vitamin A. Xeropthalmia is a condition where dryness spreads to cornea. Cornea is transparent portion on the white surface of eye. It becomes dull, lazy and dry. In young children Xeropthalmia is easy to detect, but in older children it is difficult to diagnose as the condition can also occur due to dust exposure and glare.
- Keratomalacia: This disease of eye occurs in children between the ages of 1 and 5 years. It occurs in people living for long periods on diet almost entirely devoid of vitamin A. The cornea becomes wrinkled and ulcers form on cornea. Unless early and adequate treatment is given, there is grave risk of blindness.
Daily Requirement Of Retinol
The daily requirement of retinol is:
- 300 mcg for infants and young children.
- 500 to 600 mcg for children between the ages 9 to 15 years.
- 750 mcg for adolescents and adults.
- 1200 mcg for lactating women.
Vitamin A deficiency can be prevented with better maternal and child health services, education of mothers, and improvement in food production. The prime objective should be that children should obtain adequate amount of vitamin A or carotene in their diet or as supplement.