An orange carotenoid pigment that the intestinal wall converts into vitamin A on demand. Supplements supply it as synthetic all-trans beta-carotene or as an algal or palm-derived extract, at doses many times what a diet of coloured vegetables provides.
Beta-carotene is the cautionary tale of the entire supplement industry, and everyone selling antioxidant capsules should be made to read it. Observational data were unusually consistent: people eating more carotenoid-rich vegetables developed less lung cancer. Two large randomised trials were funded to confirm it. Both found the opposite. ATBC, in 29,133 Finnish male smokers, found 18% more lung cancer in the beta-carotene arm; CARET, in smokers and asbestos-exposed workers, found 28% more lung cancer and 17% more deaths, and was stopped early. The vegetables were never the problem. The isolated, high-dose, purified compound was — and it remains the sharpest demonstration available that a nutrient in food and the same nutrient in a capsule are not the same intervention.
Provitamin A carotenoid, β-carotene, Synthetic beta-carotene
Regulation: The US Preventive Services Task Force recommends against beta-carotene supplementation for cardiovascular disease or cancer risk reduction — one of very few explicit "do not use" recommendations it has issued for a nutrient. No Tolerable Upper Intake Level was set, because the IOM concluded instead that supplemental beta-carotene is not advisable for the general population outside provitamin A deficiency.
What the research used
The amounts, forms and durations published trials of Beta-carotene (supplemental) actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for ATBC trial
20 mg
Strong
Synthetic beta-carotene capsule, daily · 5–8 years
This arm produced more lung cancer, not less. The number is recorded because it is the dose at which harm was demonstrated, not because it is a target.
Studied for CARET trial
30 mg
Strong
Beta-carotene plus 25,000 IU retinyl palmitate, daily · Stopped early after ~4 years
Terminated ahead of schedule for harm in smokers and asbestos-exposed workers.
Studied for Typical retail supplement
3–15 mg
Not enough
Softgel or multivitamin component
Often labelled in IU (5,000–25,000 IU). A dietary intake from vegetables of 3–6 mg/day is common and carries none of the trial findings above.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
Each timing below was actually compared against an alternative in a trial, which is unusual.
🍽️With food
Moderate
Carotenoid absorption depends on dietary fat and improves substantially when taken with a meal containing some. This is measurable in absorption studies rather than assumed.
Timing was tested. A trial compared this window against another and reported a difference.
The evidence in depth
Best supported: Limited
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Some trials report that several weeks of supplementation modestly raises the UV dose needed to redden skin — an effect roughly equivalent to a very low sun protection factor. It is not a substitute for sunscreen and the trials are small.
Limited evidence. Early human work, or mostly lab and animal research.
Beta-carotene was part of the original AREDS eye formulation, but it was removed in AREDS2 and replaced with lutein and zeaxanthin precisely because of the lung cancer signal in smokers. On its own it has no established macular benefit.
Not enough evidence. Not enough human research to say anything useful yet.
Beta-carotene quenches singlet oxygen in a test tube, but the large randomised trials designed on that reasoning found no benefit for cancer or cardiovascular outcomes and, in smokers, net harm. The antioxidant rationale is a good example of a mechanism that failed when tested in people.
What may be going on: At high oxygen tension — as in the lung of a smoker — beta-carotene can behave as a pro-oxidant rather than an antioxidant, one of the proposed explanations for the trial results.
Not enough evidence. Not enough human research to say anything useful yet.
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Too much
Increased lung cancer incidence in smokers and asbestos-exposed workers
Two large randomised trials — ATBC and CARET — independently found higher lung cancer incidence and higher mortality in people given 20–30 mg/day of supplemental beta-carotene who smoked or had asbestos exposure. CARET was stopped early for harm. Anyone who smokes, has smoked, or has occupational asbestos exposure should not take beta-carotene supplements. This is a landmark finding and it is not disputed.
Too much
Carotenodermia
Sustained high intake turns skin — especially palms and soles — orange-yellow. It is harmless and resolves on stopping, but it is sometimes mistaken for jaundice; the distinguishing feature is that the whites of the eyes stay white.
Interaction
Reduced absorption with fat-blocking drugs and interference with other carotenoids
Interacts withOrlistat, cholestyramine, colestipol, mineral oil
Orlistat, cholestyramine and mineral oil all reduce carotenoid absorption. In the other direction, high-dose beta-carotene competes for absorption with lutein and other carotenoids, lowering their blood levels.
Worth knowing
No pre-market safety review, and the harm is dose-related
US supplements reach shelves without pre-market efficacy or safety assessment, and beta-carotene remains freely sold at trial-harm doses, including inside multivitamins where buyers may not notice it. Reading the label matters more here than almost anywhere else in this catalogue.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.