- Vitamin A in Plant Foods
- Dietary Reference Intakes for Vitamin A
- Vitamin A Deficiency
- Vitamin A Absorption
Vitamin A in Plant Foods
Pre-formed vitamin A exists only in animal products. However, there are about 50 carotenoids that the body can convert into vitamin A, with the most common being beta-carotene. The vitamin A content of foods is measured in retinol activity equivalents (RAE). You may also see carotenoids measured in international units, or IU. One IU beta-carotene from foods is equivalent to 0.05 micrograms RAE and 1 IU beta-carotene from dietary supplements is equivalent to 0.15 micrograms RAE.
Our table of the RAE content of various plant foods has been moved to the Daily Needs page.
Dietary Reference Intakes for Vitamin A
|Dietary Reference Intakes for Vitamin A|
|≥ 19 male||900||3,000|
|> 19 female||700||3,000|
The upper limit for vitamin A applies only to the retinol form (found in animal products, fortified foods, and supplements), but does not apply to carotenoids.
Vitamin A Deficiency
Vitamin A deficiency symptoms begin with night blindness and can progress to more severe eye problems such as corneal ulcers, scarring, and blindness (1).
Vitamin A deficiency also reduces the ability to ward off infections.
Vitamin A is important for growth and development in infants and children, and for red blood cell formation.
Vitamin A Absorption
Eating vegetables high in carotenoids with some fat has been shown to increase both the absorption and synthesis of vitamin A (2).
Many factors affect how well dietary carotenoids are absorbed and converted to vitamin A, including body composition, age, smoking, medications, alcohol consumption, food processing, and genetic variation (3, 4). As many as 50% of individuals in some populations may have a low response to beta-carotene and other carotenoids, meaning they either don’t absorb as much as others do or they don’t convert as much to vitamin A (6).
Researchers are looking into how genetic variability impacts the conversion of carotenoids into vitamin A and whether recommendations should vary according to people’s genetic type (5). But at this point, it’s not possible outside of a research setting to determine if someone has a lower response to dietary carotenoids. Even so-called “low-responders” apparently can absorb some dietary carotenoids and convert some to vitamin A (7).
We don’t know the amount of provitamin A carotenoids that is optimal for a low responder who relies exclusively on carotenoids. But choosing a generous amount of foods containing beta-carotene and other provitamin A carotenoids may lead to greater absorption and more conversion in low-responders (8). Until more is known, our best advice is to meet the intake recommendations for provitamin A carotenoids by eating generous amounts of leafy green vegetables, carrots, sweet potatoes, and bright orange winter squashes.
If you have concerns about vitamin A, taking a vegan supplement providing a small amount of preformed vitamin A in the form of retinol is another option. The recommendation for a small amount is because some observational studies have found an increased risk for bone fracture with intakes of preformed vitamin A above 1,500 mcg RAE, only slightly more than the RDA (9, 10). In any case, preformed vitamin A intakes should not exceed 3,000 mcg RAE (10,000 IU) daily (11).
Last updated January 2020
2. Kopec RE, Cooperstone JL, Schweiggert RM, Young GS, Harrison EH, Francis DM, Clinton SK, Schwartz SJ. Avocado Consumption Enhances Human Postprandial Provitamin A Absorption and Conversion from a Novel High-β-Carotene Tomato Sauce and from Carrots. J Nutr. 2014 Aug;144(8):1158-66.
3. Moran NE, Mohn ES, Hason N, Erdman JW Jr, Johnson EJ. Intrinsic and extrinsic factors impacting absorption, metabolism, and health effects of dietary carotenoids. Adv Nutr. 2018 Jul 1;9(4):465-492.
6. Lietz G, Oxley A, Leung W, Hesketh J. Single nucleotide polymorphisms upstream from the β-carotene 15,15′-monoxygenase gene influence provitamin A conversion efficiency in female volunteers. J Nutr. 2012 Jan;142(1):161S-5S.
8. Borel P, Desmarchelier C, Nowicki M, Bott R. A combination of single-nucleotide polymorphisms is associated with interindividual variability in dietary β-carotene bioavailability in healthy men. J Nutr. 2015 Aug;145(8):1740-7.
11. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, 2001