Vitamin A is an umbrella term that includes several different nutrients. When you think about vitamin A and its well-known role maintaining healthy vision, you’re thinking of retinol. Retinol is just one form of vitamin A that's only found in foods from animals.
Vitamin A refers to different substances that are grouped into two categories called retinoids and carotenoids. The retinoids -- retinol, retinal and retinoic acid -- are active forms of vitamin A. The carotenoids are pigments that give fruits and vegetables their vibrant green, red, yellow and orange colors. There are hundreds of carotenoids and most work as antioxidants. Three of the carotenoids, alpha-carotene, beta-carotene and beta-cryptoxanthin, are called pro-vitamin A carotenoids because your body can convert them into retinol.
One of the best sources of retinol is beef liver, which has 4,208 micrograms in a 3-ounce serving. The next highest sources, eggs and dairy products, drop down to 80 micrograms in a large egg, 66 micrograms in 1 cup of 2 percent milk and 60 to 72 micrograms in 1-ounce of most cheeses, such as cheddar, Swiss and Parmesan. A 3-ounce serving of shrimp has 46 micrograms, while salmon, flounder and chicken breast are in the range of 6 to 10 micrograms per 3-ounce serving. You'll only get 2 micrograms of retinol from the same portion of light-meat turkey or roast beef.
Requirements and Reporting
For nutrition labeling, a measurement called international units, or IU, is used that lets you compare the amount of active vitamin A found in foods no matter which form of the vitamin they contain. One international unit is assigned to every 0.3 micrograms of retinol, 0.6 micrograms of beta-carotene and 1.2 micrograms of other pro-vitamin A carotenoids contained in the food. Men need to include 3,000 IU and women need 2,333 IU of vitamin A in their daily diets. You may also see another measurement -- retinol activity equivalents, or RAE -- that also includes the different forms of retinoids and carotenoids in food to reflect their total vitamin A activity.
A typical serving of the best sources of pro-vitamin A carotenoids has more IU of vitamin A than most foods with retinol. A 3-ounce serving of pan-fried beef liver has 22,175 IU, compared to one baked sweet potato with 28,058 IU, 1 cup of cooked carrots with 26,571 IU 1 cup of and spinach with 22,916 IU. Other good sources of pro-vitamin A carotenoids, such as winter squash, sweet red peppers, green leaf lettuce and peas, provide a range of 3,360 to 10,707 IU of vitamin A in a 1-cup serving. The next highest source of retinol, which is cheddar cheese, only has 284 IU of vitamin A in a 1-ounce serving.
- University of Maryland Medical Center: Vitamin A
- Linus Pauling Institute: Vitamin A
- Linus Pauling Institute: Carotenoids
- USDA: Composition of Foods, Raw, Processed, Prepared
- USDA National Nutrient Database for Standard Reference: Vitamin A (IU) Content of Selected Foods
- USDA National Nutrient Database for Standard Reference: Vitamin A (RAE) Content of Selected Foods
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