Ratinol

Beta-carotene, retinol, and retinal all show reliable vitamin A activity. Retinal and retinol exist in chemical equilibrium in the body and have equivalent antixerophthalmic activity. Retinal combines with the rod pigment opsin in the retina to form rhodopsin, which is needed for visual dark adaptation. Vitamin A prevents growth retardation and preserves the integrity of epithelial cells. Normal adult liver stores are enough to meet the body's vitamin A needs for about two years. Vitamin A is readily absorbed from the gastrointestinal tract, where it is also synthesized from beta-carotene. Its absorption depends on bile salts, pancreatic lipase, and dietary fat. It is carried in the blood to the liver by the chylomicron fraction of the lymph and is stored in the liver's Kupffer cells, mainly as retinol palmitate. Normal serum vitamin A levels are 80 to 300 units per 100 mL (a plasma range of 30 to 70 mcg per dL), and carotenoid levels are 270 to 753 units per 100 mL. The normal adult liver contains roughly 100 to 300 micrograms per gram, mostly in the form of retinol palmitate.

Nobody has established that vitamin A is safe in amounts above 6,000 Units a day during pregnancy. Taking more than the recommended dietary allowance can harm the unborn baby when given to a pregnant woman. In animal reproduction studies, overdosage caused abnormalities in the fetus in several species. The malformations recorded affect the central nervous system, the eye, the palate and the urogenital tract.

For this reason, vitamin A above the recommended dietary allowance is contraindicated in women who are pregnant or who may become pregnant. If vitamin A is used during pregnancy, or if a patient becomes pregnant while taking it, she should be told about the possible hazard to the fetus.

For nursing mothers, the U.S. Recommended Daily Allowance (RDA) of vitamin A is advised, which is 5,000 Units.

Store Vitamin A below 25°C, and keep it away from light and moisture. Keep it out of the reach of children.