Sources of Preformed Vitamin A
There are two sources of vitamin A that occur in nature: preformed and provitamin (also known as carotene). Preformed vitamin A is derived from animal sources and very easy for the body to absorb. It's fat soluble, meaning that lipids, or fats, are necessary for its absorption. As such, it's possible to overdose on this vitamin. Carotene is found in plants, especially dark-colored fruits and vegetables. This type of the vitamin is water soluble, so there's little chance of overdose, but it's also less easily absorbed by the body.
Liver
Beef and chicken liver are rich, natural sources of preformed vitamin A. In three ounces of beef liver, there are 30,000 IU (International Unit) of the vitamin, while there are 13,000 IU in the same amount of chicken liver.
Dairy
Preformed vitamin A is prevalent in dairy products such as milk, butter and cheese. Whole milk has around 300 IU in every cup. Butter has about 450 IU per tablespoon, and cheese has about 250 IU per ounce. Low-fat and skim dairy products are often fortified with vitamin A to make up for the loss incurred by stripping the foods of fat.
Eggs
Along with vitamins D and E, eggs are a rich natural source of preformed vitamin A. However, all the vitamins are located in the egg yolk; the whites provide protein but significantly less nutritional content.
Fish Oil
The greatest concentrated source of vitamin A available is fish oil, which is derived from fish livers. The fish themselves are not as high in preformed vitamin A, but their livers pick it up (along with omega-3 fatty acids) when the fish consume external sources of the vitamin, such as algae.
Recommended Dose
For an adult male (14 or older), the recommended daily amount of vitamin A is 3,000 IU. The dose is lower for females 14 and up: 2,310 IU. Be careful not to exceed the daily dosage, because consuming too much vitamin A (hypervitaminosis A) can lead to vomiting, blurred vision, hair loss, birth defects, osteoporosis and liver problems.
Benefits
An appropriate amount of vitamin A is essential for vision, reproduction, bone and cell growth and the immune system. Vitamin A also helps prevent bacteria from entering the body by creating healthy linings for the eyes, the intestines, urinary and respiratory tracts, as well as supporting the skin and mucus membranes.
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