Beta-Carotene: Food Sources, Supplements and Safety

Carotenoids are plant pigments. Beta-carotene is one that can be converted into vitamin A; retinol and retinyl esters are preformed vitamin A. A supplement can contain either form or a mixture. Read the ingredient name rather than assuming every vitamin A product contains the same substance.^{See reference 1}

Vitamin A activity is expressed in retinol activity equivalents (RAE). Food beta-carotene, supplemental beta-carotene and preformed vitamin A do not provide identical vitamin A activity per microgram. A mass of beta-carotene is therefore not automatically the same mass of retinol or the same RAE value.^{See reference 2}

ATBC randomly assigned participants to four groups. Beta-carotene groups had 18% higher lung-cancer incidence than groups without beta-carotene, with a 95% confidence interval from 3% to 36% higher. This is a relative increase in that study population, not 18 additional cases per 100 people and not an estimate for every user.^{See reference 3}

CARET used beta-carotene together with preformed vitamin A. The combination group had a lung-cancer relative risk of 1.28 (95% confidence interval 1.04–1.57) compared with placebo. The intervention was stopped early. These results challenge the assumption that an antioxidant mechanism guarantees a beneficial supplement outcome.^{See reference 4}

A food pattern supplies many nutrients and other components together. Observational links between carotenoid-rich diets and health cannot prove that isolated beta-carotene caused the outcome. Randomised supplement trials are a different test, and in the populations above they found harm.^{See reference 6}

The smoker-trial warning is about concentrated supplements, not advice to avoid carrots or spinach. NIH guidance identifies smokers, former smokers and asbestos-exposed people as groups for whom high-dose supplemental beta-carotene is a concern. Check mixed products as well as single-ingredient bottles.^{See reference 1}

AREDS-type combinations are intended for particular stages of age-related macular degeneration. The National Eye Institute explains why lutein and zeaxanthin replaced beta-carotene in the AREDS2 formulation, including lung-cancer concerns for people with a smoking history. These studies do not make every carotenoid product suitable for every adult.^{See reference 5}

If a clinician has recommended an eye supplement, discuss its exact formulation and your smoking history with the eye-care team. Do not treat a generic beta-carotene bottle as an interchangeable version of the studied combination.^{See reference 5}