“Free retinol is not generally found in food. Retinyl esters (including retinyl palmitate) are the storage form of retinol in animals and thus the main precursors of retinol in food from animals. Plants contain carotenoids, some of which are precursors for vitamin A (e.g., α-carotene, β-carotene, and β-cryptoxanthin). Yellow- and orange-colored vegetables contain significant quantities of carotenoids. Green vegetables also contain carotenoids, though yellow-to-red pigments are masked by the green pigment of chlorophyll (1). The table below lists a number of good food sources of vitamin A, including fruit and vegetables, along with their vitamin A content. The retinol activity is indicated in micrograms of retinol activity equivalents (μg RAE). For information on this unit of measurement, see the section on RAE. In addition, use the USDA food composition database to check foods for their content of carotenoids without vitamin A activity, such as lycopene, lutein, and zeaxanthin.
Vitamin A international units (IUs)
Vitamin A is currently listed on food and supplement labels in international units. The USDA database also provides the vitamin A content of food sources using the vitamin A international unit (IU). Yet, contrary to RAE, the number of IUs of vitamin A does not reflect the bioavailability of vitamin A from different food sources. Conversion rates between IUs and μg RAE are set as follows:
• 1 IU of retinol is equivalent to 0.3 μg RAE
• 1 IU of supplemental β-carotene is equivalent to 0.15 μg RAE
• 1 IU of dietary β-carotene is equivalent to 0.05 μg RAE
• 1 IU of α-carotene or β-cryptoxanthin to 0.025 μg RAE
Thus, in Table 3, the number of IUs of vitamin A in carotenoid-containing food (numbers in italics) can be obtained by multiplying the RAE by approximately 20.