Vitamin A is released as needed into the bloodstream, becoming available for use by cells throughout the body, including those of the eye.
Vitamin A is a fat soluble substance found in ester form in animal and dairy products. It is hydrolyzed in cells of the small intestine to alcohol.
About half the dietary vitamin A intake comes from animal food sources as preformed vitamin A, retinoid. The other half of dietary vitamin A intake comes from fruits and vegetables in the form of pro-vitamin A carotenoids especially beta carotenes. Whole eggs, whole milk, and liver are among the few foods that naturally contain vitamin A. Vitamin A is present in the fat portion of whole milk.
There are many other fortified foods such as breakfast cereals that also provide vitamin A. Carotene, the naturally occurring progenitor of vitamin A found in certain vegetables and fruits, is split in the intestinal cells to retinaldehyde, most of which is promptly reduced to retinol.
It is important to regularly eat foods that provide vitamin A or beta-carotene even though the body can store vitamin A in the liver. Stored vitamin A will help meet body needs when the intake from food is low.
Vitamin A functions to maintain normal reproduction, vision and immune function. Vitamin A allows human to see in dim light and plays a role in the production of tears, which lubricate and moisten the eye.
People without enough of this vitamin develop eyes that are so dry and ulcerated that the cornea can burst, leading to total blindness.
Vitamin A
