Beta carotene is a member of the carotenoid family belonging to the isoprenoid compounds, which are polyunsaturates with antioxidant properties. The formula for beta carotene is C40H56 and it can exist as cis- or trans-isomers. Most of the naturally-occurring and synthesized forms of beta exists as the all-trans isomer.
Where is beta carotene found?
Beta carotene is produced by plants and microorganisms, with the main sources being yellow or orange and green-leaved vegetables or fruits such as sweet potato, spinach, carrots, pumpkin, butternut squash and apricots.
Beta carotene is also available as supplements, which may be synthetic or derived from palm oil, algae or fungi. When taken as a vitamin or mineral supplement, the dose ranges form 0.4 mg to 20 mg per day.
When used as a medicine to treat vitamin A deficiency, a dose of up to 6 mg/day may be given and in cases of erythropoietic protoporphyria (EPP), up to 300 mg/day may be taken. Beta carotene is also widely used as a yellow colouring agent (EC160a) in food and drink.
Although beta carotene is not classed as an essential nutrient, it is a precursor to vitamin A and the recommended daily intake is expressed as part of the reference nutrient intake (RNI) for vitamin A as retinol equivalents (RE).
Beneficial effects of beta carotene
As a provitamin of vitamin A, the importance of beta carotene in an individual depends on their level of pre-formed vitamin A. It is therefore difficult to define a beta- carotene deficiency. Beta carotene also interacts with other carotenoids during absorption and metabolic processes.
Studies have shown an association between high dietary intake of beta carotene and a reduced risk of heart disease and cancer. This may be due to the antioxidant properties of the molecule.
The absorption of beta carotene is facilitated by dietary fats and bile salts in the small intestine. Around 10% to 90% of the total dietary beta carotene is thought to be absorbed in the gut, with absorption decreasing, the higher the intake is. Low fat diets also reduce the amount of beta carotene absorbed.
Smokers have a low blood level of beta carotene, as do individuals with a high alcohol intake and those with HIV infection. People with impaired fat absorption from diet due to conditions such as jaundice, liver cirrhosis and cystic fibrosis also have a low blood level of beta carotene. Beta carotene is excreted in the feces and sweat.
Reviewed by Sally Robertson, BSc