Preformed Vitamin A (Retinol) vs Beta-Carotene: Differences in Conversion and Safety

Safety first

Taking too much preformed vitamin A can make you seriously ill, and large amounts in pregnancy can cause birth defects. [1] Babies and children are more sensitive and can become sick on smaller amounts. [1] If a child may have swallowed vitamin A or any vitamin product, call Poison Help at 1-800-222-1222 (US) or 911 if the child is unwell; other countries are listed on Poison Help by country. People who smoke, and people who have been exposed to asbestos at work, are advised by the NHS (UK) not to take any beta-carotene supplements. [2] Do not stop or change a prescribed medicine, including acne or skin retinoids, without your prescriber. See vitamin A excess, pregnancy and retinoid medicines.

The short answer

Both are routes to vitamin A, but they are not the same product. Preformed vitamin A (retinol and its esters, such as retinyl palmitate or retinyl acetate) comes from animal foods and supplements and is ready to use. Provitamin A carotenoids, mainly beta-carotene, come from plants and must be converted by the body. [1] Carotenoids from food behave very differently from beta-carotene taken as a high-dose pill, and the two forms carry different risks. There is no universal winner; the choice is made through diet and, where needed, a clinician.

Evidence labels used here: established nutritional role, evidence of harm, no good evidence of benefit, mixed. Proper evidence not found means we looked and found nothing usable.

Documented differences

Beta-carotene pills and lung cancer

Two large randomized trials found harm in high-risk groups. In ATBC, 29,133 male smokers in Finland took 20 mg of beta-carotene a day, 50 mg of vitamin E, both or placebo for 5 to 8 years; lung cancer was 18% higher in men who got beta-carotene. [5] In CARET, 18,314 smokers, former smokers and asbestos-exposed workers took 30 mg of beta-carotene plus 25,000 IU of retinol (as retinyl palmitate) daily; lung cancer risk was 28% higher and the trial was stopped early. [6] Because CARET tested the two together, it cannot say which caused the harm. These are study amounts, not advice. MedlinePlus says eating foods rich in beta-carotene may reduce cancer risk, but beta-carotene supplements do not and may raise it in current and former smokers. [1] Label: evidence of harm for supplements in these groups; no good evidence of benefit for cancer prevention.

Retinol versus retinyl palmitate

Retinol and retinyl esters are both counted as preformed vitamin A, and supplements usually use the ester forms. [1] [3] Proper evidence not found in the sources we read for a safety or benefit difference between retinol and retinyl palmitate in people (we searched PubMed for head-to-head comparisons).

Official intake and upper levels

The NHS also advises keeping vitamin A from food and supplements to 1.5 mg (1,500 mcg) a day or less on average, because over many years more may affect bones, especially in older women. [7] The units are different from one country to another and from IU, so see vitamin units explained.

Who needs extra care

Pregnancy (including liver and liver pâté, which the NHS says to avoid), young children, older adults at risk of osteoporosis, people with liver disease, and people taking retinoid medicines should ask a clinician first. [7] Check labels on multivitamins and fish liver oils, which can contain vitamin A. [7] See quality testing and certifications.

Related pages

Vitamin A profile | Carotenoids | Foods high in vitamin A