Vitamin A, also called retinol, is a fat-soluble vitamin that is essential for humans. Adequate intake is important for normal vision and immune function. Dietary vitamin A can be provided as both preformed vitamin A and provitamin A carotenoids that are precursors to vitamin A. Preformed vitamin A is abundant in animal-derived foods like liver, kidney, eggs, and dairy products. Carotenoids, like beta-carotene, are found in darkly colored fruits and vegetables. Preformed vitamin A is efficiently absorbed through the intestines, while carotenoids may either be absorbed through the intestines intact or cleaved to form vitamin A prior to absorption. The proportion of beta-carotene converted to vitamin A decreases as beta-carotene intake increases, limiting the risk of vitamin A toxicity 1.
Beta-carotene, also called provitamin A, is a member of a group of plant-produced compounds called carotenoids, which serve as precursors to vitamin A. Beta-carotene is a potent antioxidant. The ultimate source of all vitamin A is from the carotenes, and beta-carotene has the highest vitamin A activity 2. Beta-carotene is particularly abundant in orange vegetables and fruit, and may be directly added to foods as a vitamin supplement 3.
Carotenoids may either be absorbed through the intestines intact, or be cleaved to form vitamin A prior to absorption. There is no Recommended Dietary Allowance (RDA) for beta-carotene or other provitamin A carotenoids. However, dietary provitamin A carotenoids have vitamin A activity that can be expressed as retinol activity equivalents (RAEs). The RDA for RAEs is 900 µg/day for men and 700 µg/day for women 1. Beta-carotene supplementation in humans is likely safe over long periods of time.
Blakeslea trispora is a fungus that can be used as a source of carotenoids, such as beta-carotene, gamma-carotene and lycopene, for dietary supplements 4,5.