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Vitamin A is essential throughout life, beginning in the earliest stages. It is required for cell differentiation, the process that determines the function of new cells. This makes vitamin A especially important during fetal development and childhood growth, periods with the highest rates of cell differentiation. Throughout life, vitamin A remains necessary for growth, vision and fighting disease.

The body makes vitamin A from precursors in the diet – either retinyl esters from animal products (and fortified foods) or carotenoids from plants. These precursors can be changed to three forms of vitamin A: retinol (the most common), retinal and retinoic acid. As a group, retinyl esters, retinol, retinal and retinoic acid are called retinoids.

The body is more efficient at transforming retinyl esters into vitamin A than carotenoids (a type of pigment produced by some plants). Therefore, it requires larger amounts of carotenoids than retinyl esters to make the same amount of vitamin A. The best sources of carotenoids are yellow and orange fruits and vegetables, including carrots, mangos and sweet potatoes.

Supplements may be recommended by physicians for people who do not consume enough vitamin A through the diet or as part of the treatment for various conditions. They are available as preformed retinol (ready to be used by the body), beta carotene (must be converted to be used) or a combination of both. However, vitamin A supplementation does significantly increase the risk of overdose. Getting too much vitamin A can lead to birth defects, osteoporosis, liver damage, central nervous system disorders and other problems.