A Requirements and the different forms of Vitamin A
Vitamin A is found in food sources in two different forms. Retinal is the active form of Vitamin A and is found in meat and dairy food sources. Carotenoids are found in fruits and vegetables and are converted by the body into the active form of Vitamin A. The most commonly known Carotenoid is Beta Carotene, for which carrots are well known. Vitamin A obtained directly from meat, or Vitamin A converted from carotendoids, both function the same way inside the body.
The daily recommended amount of Vitamin A is 5000 IUs. Obtaining the recommended daily allowance of vitamin A is not difficult because many foods contain more than 5000 IUs in a single serving. Keeping track of Vitamin A consumption from lesser sources can be difficult though, because different carotenoids each convert to different amounts of Vitamin A and the conversion is dependant upon the amount of Vitamin A already in the body. Those who have plenty of Vitamin A already in their systems will not convert as much as someone with a deficiency.
The second reason it is difficult to track Vitamin A consumption is because the cooking method used will have a drastic effect on the amount available. Cooking meat destroys some of the Retinal found in the food, and boiling vegetables and discarding the water will result in the loss of a good amount of the carotenoids. The good news is that the major sources of Vitamin A have such large amounts that even cooking or boiling those foods will still result in more than a full days supply of Vitamin A.
Food sources rich in Vitamin A, dairy and meat
Vitamin A is found in all meats and dairy products, in many cases however, these sources only provide minimal amounts of Vitamin A once cooked. The major exception to this rule is liver which will supply more than the recommended daily allowance with even a small serving. Other meat and dairy products that are a good source of vitamin A in their edible forms include eggs, butter and cheese. Most of the Vitamin A found in milk is destroyed during pasteurization, but in many countries, the milk is later enriched with Vitamin A. Cod Liver Oil, which is a common supplement, contains large amounts of Vitamin A.
Food sources rich in beta carotene and other caratenoids, fruits and vegetables
Carotenoids such as Beta Carotene come from fruits and vegetables and are changed into functional Vitamin A inside the body. Carotenoids have bright colors, so generally all red, orange or yellow fruits or vegetables contain large amounts of Vitamin A. Also dark, leafy vegetables like spinach contain high amounts of Vitamin A. There are a few things that can be done to increase the amount of Vitamin A obtained from plants sources. The first is to make juices using a blender. This will help destroy the cell walls and allow more of the carotenoids to be absorbed in the intestines. Also, it is best if carotenoids are consumed with foods that contain fat. Fat is needed to transport carotenoids through the lining of the small intestines. Finally, when cooking, it is best to either steam the vegetables or to consume the water used (like soup) because much of the nutritional value of the food will be found in the water after boiling.
Functions of Vitamin A
Vitamin A performs many important functions in the body, but it's function in vision often leads to the most notable side effect of deficiency, poor vision, especially in dim lighting. Vitamin A is also important for the immune system. Most causes of deficiency involve a medical condition that diminishes absorption in the small intestines. Alcoholism is also a leading cause of Vitamin A deficiency, mainly because the liver is an important part of fat digestion, which also affects the absorption rates of many nutrients.
Summary of information about Vitamin A food sources
Vitamin A can be consumed in two forms. The active form of Vitamin A can come directly from animal products such as liver, cheese and eggs. Cooking will reduce the amount of Vitamin A these foods provide, but they will still give large amounts. Because these foods contain other things that are not helpful to good nutrition like cholesterol, it is usually recommended that the majority of Vitamin A come from plant sources. Plants provide Carotenoids, which are transformed inside the body into the active form of Vitamin A. Carrots, brocolli, leafy vegetables and dark colored fruit are all a good source of beta carotene and vitamin A along with many other vitamins and minerals.