Vitamins >> Vitamin A deficiency

Vitamin A deficiency and vision
Vitamin A deficiency among children in developing nations is the leading preventable cause of blindness. The earliest evidence of vitamin A deficiency is impaired dark adaptation or night blindness. Mild vitamin A deficiency may result in changes in the conjunctiva (corner of the eye) called Bitot's spots. Severe or prolonged vitamin A deficiency causes a condition called xeropthalmia (dry eye), characterized by changes in the cells of the cornea (clear covering of the eye) that ultimately result in corneal ulcers, scarring, and blindness.

Vitamin A deficiency and infectious disease

Vitamin A deficiency can be considered a nutritionally acquired immunodeficiency disease. Even children who are only mildly deficient in vitamin A have a higher incidence of respiratory disease and diarrhea, as well as a higher rate of mortality from infectious disease, than children who consume sufficient vitamin A. Supplementation of vitamin A has been found to decrease the severity of and deaths from diarrhea and measles in developing countries, where vitamin A deficiency is common. HIV-infected women who were vitamin A deficient were three to four times more likely to transmit HIV to their infants. The onset of infection reduces blood retinol levels very rapidly. This phenomenon is generally believed to be related to decreased synthesis of retinol binding protein (RBP) by the liver. In this manner, infection stimulates a vicious cycle, because inadequate vitamin A nutritional status is related to increased severity and likelihood of death from infectious disease.

The Recommended Dietary Allowance (RDA)

The RDA for vitamin A was revised by the Food and Nutrition Board (FNB) of the Institute of Medicine in 2001. The latest RDA is based on the amount needed to ensure adequate stores of vitamin A in the body to support normal reproductive function, immune function, gene expression, and vision.