Vitamin A, a fat soluble nutrient has an important role in embryonic growth, vision and resistance to infection.
It is also involved in the regulation of various physiological functions such as gene expression, maintenance of immune system and red blood cell production.
Vitamin A is a generic term for all retinoids that qualitatively exhibit the biological activity of all-trans retinol. It has a clearly defined role in vision: when retinal tissue is deprived of vitamin A, rod and cone function is impaired.
It is also required for the integrity of epithelial cells throughout the body, via the regulatory action of retinoic acid at the level the gene.
A main dietary source of vitamin A are the carotenoids from fruits and vegetables. These carotenoids seem to have separate function as antioxidants in addition to their provitamin A function.
Active vitamin A is found only in animal sources. It is especially high in the fish liver oil from cod, halibut, salmon and shark. It is also found in beef and chicken liver and in eggs and dairy products.
Beta carotene, the vitamin A precursor, is found only in green and yellow orange fruits and vegetables, such as carrots, kale, kohlrabi, parsley, spinach turnip green and cantaloupe.
Vitamin A deficiency is rare in the US, but it is still a major public health problem in the developing world. It is most often associated with protein/calorie malnutrition and affects over 120 million children worldwide.
As early as 1500 BC, clinical symptoms of vitamin A deficiency such as night blindness were described by the Egyptians. Furthermore, the importance of vitamin A for resistance to infectious disease has been known for almost hundred years.
Extremely dry skin, dry hair, sloughing off of skin, and broken fingernails are other common signs of vitamin A deficiency. Vitamin A deficiency also decreases resistance to infections, and may contribute to the pneumonia associated with vitamin A deficiency.
Roles of vitamin A in human body
