Loss Of Vitamins As A Cause Of Blindness

According to the World Health Organization, vitamin A deficiency is the leading cause of preventable blindness among children and is considered a public health concern in more than half of all countries. While vitamin A deficiency can occur as a result of underlying medical conditions, it usually develops from inadequate dietary intake of the vitamin.

Physiology of Vision

Vitamin A allows your eyes to translate light images into vision. Light enters your eye through your cornea and travels to the retina in the back of your eye. Your retina contains two light-sensitive proteins, rhodopsin and iodopsin, which are located in the structures referred to as rods and cones. Rhodopsin and iodopsin are rich in vitamin A and rely on the vitamin to provide you with vision.

When light reaches rhodopsin, the protein absorbs the light, the shape of the vitamin A is changed and the vitamin eventually detaches from the protein. This series of events, called bleaching, sends messages through your optic nerve, which transmits as visual images to your brain. After bleaching, vitamin A reattaches to the protein and returns to its normal shape.

Vitamin A Deficiency

If you do not have enough vitamin A in your body, the light-sensitive proteins in your eye lack the vitamin A necessary to create visual images. A vitamin A deficiency initially manifests as night blindness, which is defined as difficulty seeing after dusk. Night blindness is due to an inability to regenerate rhodopsin, which prevents the eyes from adjusting from daylight to darkness.

Vitamin A deficiency, if untreated, can lead to a condition called xerophthalmia, which is characterized by severe dryness and damage to the cornea. Severe xerophthalmia can lead to blindness. "Nutrition and You" by Joan Salge Blake notes that up to 10 million children suffer from xerophthalmia annually and 500,000 of them go blind.

Considerations

Blindness from vitamin A deficiency is most common in developing regions, especially southeast Asia. This occurs because the prominent food, rice, does not contain vitamin A. Young children and pregnant women in low-income areas represent the highest-risk group for blindness from vitamin A deficiency.

Prevention

Meeting your needs for vitamin A is the only way to prevent a vitamin A deficiency. It is recommended that infants between the ages of 0 and 6 months receive 400 mcg per day, whereas infants from 6 to 12 months need 500 mcg daily. Children between 1 and 3 years old should consume 300 mcg per day, children between 4 and 8 need 400 mcg daily and children from 9 to 13 require 600 mcg per day. Teenagers and men aged 14 and older should consume 900 mcg per day, whereas females of the same age require 700 mcg daily.

The best food sources of vitamin A include leafy, dark green vegetables, oranges, carrots, squash, pumpkin and egg yolks. In the United States, many foods, such as milk and cereal, are fortified with vitamin A.