Betacarotenes

Betacarotenes are a group of carotenoids that function as provitamin A compounds in humans. The most abundant member is all-trans-beta-carotene, but many natural and synthetic isomers exist. They are orange pigments found in a wide range of plants and are fat-soluble, accumulating in body lipids.

Chemically, beta-carotene has the formula C40H56 and consists of two beta-ionone rings joined by a long polyene chain. The all-trans configuration predominates in nature, but processing and storage can generate cis isomers, which may have different bioavailability and activity.

Dietary sources include orange and dark-green vegetables and fruits such as carrots, sweet potatoes, pumpkins, cantaloupe, spinach, and kale. Bioavailability is influenced by food preparation and the presence of dietary fat; cooking can improve release from plant matrices and fats aid intestinal absorption.

Biological activity and metabolism: beta-carotene is a precursor to vitamin A. In the intestine, enzymes such as BCO1 cleave beta-carotene to retinal, which is reduced to retinol (vitamin A) and then stored or transported to tissues. Retinol activity equivalents (RAE) estimate vitamin A activity: about 12 μg of dietary beta-carotene equals 1 μg retinol, while supplemental beta-carotene has a lower conversion efficiency (about 24 μg beta-carotene per 1 μg retinol).

Health implications: diets rich in beta-carotene-containing foods contribute to vitamin A status and may be associated with reduced risk of certain deficiencies. However, high-dose beta-carotene supplements have not shown consistent cancer-prevention benefits and, in some trials with smokers, were associated with increased lung cancer risk. Very high intake can cause carotenodermia (orange skin) but is not known to cause vitamin A toxicity from food sources alone. Therefore, beta-carotene is generally recommended primarily from dietary sources rather than supplements.