A deficiency in Vitamin A is the second-leading cause of blindness in the developing world, said Stephen McGowan, MD, professor in the University of Iowa Department of Internal Medicine.

"Vitamin A is most critical for vision, but it is also important for the maintenance of the skin, lungs, and intestinal tract," McGowan said.

Vitamin A is found in meat and dairy products, as well as fruits and vegetables. It is a fat-soluble substance that is divided into retinol and provitarnin A. Retinol is the active form of vitamin A usually found in animal products, while provitamin A is found in fruits and vegetables. Three times as much provitamin A has to be eaten by way of fruits and vegetables in order to get the same amount of retinol that would be acquired in the consumption of animal products.

"Meat, eggs and milk (most dairy products are fortified with vitamin A), as well as carrots, yellow squash and pumpkins are good sources of vitamin A," McGowan said.

Other sources of vitamin A to keep in mind are fish, butter or cream, cheese, spinach, cassava, sweet potatoes, papaya, and mangos. Not all yellow and orange fruits and vegetables fall into this list, however. Citrus fruits do not contain any vitamin A.

Because many American foods are fortified with vitamin A, deficiency is very rare in individuals who do not have certain chronic intestinal illnesses. In developing regions such as Africa, Asia, South America, and the Western Pacific, vitamin A deficiency is most prevalent in women who are pregnant or lactating and in children 18 months to 8 years old, McGowan said.

"Babies use more vitamin A because they are growing at such a rapid pace," McGowan said. "Vitamin A deficiency is most commonly encountered after the child has been weaned off breast milk because the child is no longer getting a natural source of vitamin A."

Supplements of vitamin A are also used to help correct the deficiency or prevent if from occurring.

"Premature infants are at risk for vitamin A deficiency and are often given supplements after birth," McGowan said. "Too much vitamin A given to children could be toxic, while too little increases a child's risk for infection."

Women in their first trimester of pregnancy should also be careful not to take too much vitamin A, but they should also make sure not to take too little, McGowan said.

"People tend to think more is better and that isn't always the case," McGowan said. "More can sometimes be dangerous."

If you have questions or are unsure about the types of vitamins you or your family should be getting, ask your doctor.