Beta-Carotene (The Provitamin-A Carotenoid Antioxidant)

Beta-carotene is the orange-red pigment that colors carrots, sweet potatoes, and pumpkins. It is the most abundant and best-known of the provitamin-A carotenoids — the body cleaves a single beta-carotene molecule into two molecules of retinol (vitamin A) exactly as needed, making it a self-regulating, non-toxic source of vitamin A. Beyond its vitamin-A role, beta-carotene is a potent lipid-phase antioxidant and the single most efficient quencher of singlet oxygen known in biology. Crucially, its safety story is split: beta-carotene from food and whole-food sources is unambiguously beneficial, but two large trials (ATBC 1994 and CARET 1996) showed that high-dose synthetic beta-carotene supplements increased lung-cancer risk in smokers and asbestos-exposed workers. That paradox — helpful nutrient, harmful isolated megadose — is the central lesson of this page.

Table of Contents

1. What Beta-Carotene Is: A Provitamin-A Carotenoid
2. Conversion to Retinol (Vitamin A)
3. Antioxidant Mechanism: Singlet-Oxygen Quenching
4. Dietary Sources
5. Benefit: Eye Health & Vision
6. Benefit: Skin Health & Photoprotection
7. Benefit: Immune Function
8. Benefit: Antioxidant Status & Lipid Protection
9. Benefit: Cognitive & Vascular Aging
10. The ATBC & CARET Trials: The Smoker Paradox
11. Dietary Intake & Supplement Dosing
12. Cautions and Contraindications
13. Key Research Papers
14. Connections

What Beta-Carotene Is: A Provitamin-A Carotenoid

Beta-carotene (β-carotene) is a tetraterpenoid pigment built from eight isoprene units — a 40-carbon chain capped at each end by a beta-ionone ring. The molecule's defining feature is a long backbone of eleven conjugated carbon-carbon double bonds. This run of alternating single and double bonds is a delocalized "electron highway" that both absorbs visible light in the blue-green range (so the molecule appears orange-red to our eyes) and gives the molecule its remarkable ability to absorb and dissipate the energy of reactive oxygen species.

Carotenoids are divided into two families. The carotenes — beta-carotene, alpha-carotene, and lycopene — are pure hydrocarbons containing only carbon and hydrogen. The xanthophylls — lutein, zeaxanthin, beta-cryptoxanthin, and astaxanthin — carry oxygen atoms on their ring structures. Beta-carotene sits in the carotene family and is the most abundant carotenoid in the human diet and in human plasma after lycopene and lutein.

What makes beta-carotene a provitamin A is that its two beta-ionone rings are the exact structural unit the body needs to manufacture retinol. Each beta-carotene molecule is symmetric, with a beta-ionone ring on both ends, which is why it can in principle yield two molecules of vitamin A. By contrast, alpha-carotene and beta-cryptoxanthin have only one beta-ionone ring and therefore yield only one molecule of retinol; lycopene and lutein have no beta-ionone ring at all and cannot become vitamin A. This is the structural reason beta-carotene is the most efficient dietary provitamin-A carotenoid.

The term "carotene" itself comes from the Latin carota (carrot), from which the pigment was first isolated by Heinrich Wackenroder in 1831. Its connection to vitamin A — that animals could make the vitamin from the plant pigment — was established in the 1930s, work that ultimately won Paul Karrer a share of the Nobel Prize in Chemistry for determining its structure.

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Conversion to Retinol (Vitamin A)

The conversion of beta-carotene into vitamin A is one of the elegant self-regulating systems in human nutrition. In the cells lining the small intestine (and to a lesser extent the liver), an enzyme called beta-carotene 15,15'-monooxygenase (BCO1) cleaves beta-carotene symmetrically at its central double bond, producing two molecules of retinal. Retinal is then reduced to retinol (the storage and transport form of vitamin A) or oxidized to retinoic acid (the active hormone form). A second enzyme, BCO2, performs an asymmetric, off-center cleavage that is important for clearing other carotenoids.

The critical safety feature is feedback regulation. When the body's vitamin A stores are adequate, retinoic acid suppresses transcription of the BCO1 enzyme. Conversion slows down, and excess beta-carotene is simply stored in fat tissue and skin or excreted — it is not forced into becoming vitamin A. This is why you cannot develop vitamin A toxicity from eating carrots or sweet potatoes, no matter how many you eat. The body throttles its own production. By contrast, preformed vitamin A (retinol/retinyl esters from liver, fish-liver oil, and high-dose supplements) bypasses this checkpoint entirely and can accumulate to toxic, even teratogenic, levels.

Conversion efficiency is far lower and more variable than the textbook ratios once suggested. The old 6:1 figure (6 micrograms of dietary beta-carotene equaling 1 microgram of retinol) has been replaced by a 12:1 ratio for beta-carotene in a mixed diet (and 24:1 for other provitamin-A carotenoids), reflected in the modern Retinol Activity Equivalent (RAE) system. Several factors lower real-world conversion:

• Genetics — common polymorphisms in the BCO1 gene reduce enzyme activity by up to 50% in a large fraction of the population, creating "low converters" who get less vitamin A from a plant-based diet.
• Food matrix — beta-carotene locked inside raw, intact plant cells is poorly absorbed. Cooking, chopping, pureeing, and especially adding fat dramatically increase bioavailability. Beta-carotene from a raw whole carrot is far less available than from cooked, mashed carrot eaten with oil.
• Fat intake — as a fat-soluble compound, beta-carotene needs dietary fat (and bile) for micelle formation and absorption. A few grams of fat in the same meal can multiply absorption several-fold.
• Vitamin A and iron status — conversion increases when the body is deficient in vitamin A and may be impaired by poor thyroid function, zinc deficiency, and intestinal disease.

This self-limiting biology is exactly why beta-carotene is a safer everyday source of vitamin A activity for most people than preformed retinol — the topic is explored further on the Vitamin A page.

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Antioxidant Mechanism: Singlet-Oxygen Quenching

Independent of any vitamin-A activity, beta-carotene is one of nature's most effective antioxidants in the lipid (fat) phase of cells — the membranes and lipoproteins where water-soluble antioxidants like vitamin C cannot reach. Its antioxidant power comes from two distinct mechanisms.

1. Singlet-oxygen quenching. Singlet oxygen is an unusually reactive, high-energy excited state of the oxygen molecule, generated by ultraviolet light, photosensitizing reactions, and certain immune processes. It is intensely damaging to DNA, proteins, and unsaturated membrane lipids. Beta-carotene is the most efficient biological quencher of singlet oxygen known. Its long conjugated double-bond system absorbs the excess electronic energy from singlet oxygen, converting the oxygen back to its harmless ground state and dissipating the energy as harmless heat. A single beta-carotene molecule can quench up to a thousand singlet-oxygen molecules before being chemically consumed — it acts almost catalytically. This is the same mechanism plants use to protect their photosynthetic machinery from light damage, which is why carotenoids are universal in green tissue.

2. Free-radical chain-breaking. Beta-carotene also scavenges peroxyl radicals (the propagating species in lipid peroxidation) by adding the radical onto its conjugated chain, forming a relatively stable, resonance-delocalized carbon-centered radical that halts the chain reaction. Notably, this radical-trapping behavior is most protective at the low oxygen tensions found in most body tissues. At the unusually high oxygen partial pressures found in the lung — especially the smoke-damaged lung — the beta-carotene radical can instead react with oxygen and behave as a pro-oxidant. This oxygen-tension dependence is one of the leading biochemical explanations for why high-dose beta-carotene proved harmful specifically in the lungs of smokers (see the safety section below).

Beta-carotene does not act alone. It works inside an antioxidant network, where it is regenerated by vitamins C and E and cooperates with glutathione-based defenses. This network behavior is why isolated, high-dose single-antioxidant supplements behave so differently from the same compound delivered in a food matrix alongside hundreds of cooperating phytochemicals.

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Dietary Sources

Beta-carotene is found almost exclusively in plant foods, where it produces orange, yellow, and (masked by chlorophyll) deep-green coloring. As a rule of thumb, the more intense the orange or the darker the green, the higher the beta-carotene content.

• Carrots — the archetypal source. One medium cooked carrot supplies roughly 8–12 mg of beta-carotene. Cooking and pureeing markedly increase bioavailability over raw.
• Sweet potatoes — among the richest common foods; a single baked sweet potato with skin can provide well over 10 mg, often exceeding a full day's vitamin-A activity in one serving.
• Pumpkin and winter squash (butternut, kabocha, acorn) — very high; canned pumpkin is especially concentrated and well-absorbed.
• Dark leafy greens — spinach, kale, collard greens, Swiss chard, and turnip greens are paradoxically high in beta-carotene; the orange pigment is simply hidden under green chlorophyll.
• Other orange produce — cantaloupe, mango, apricots (especially dried), red and orange bell peppers.
• Herbs and concentrates — cilantro, parsley, and dried herbs are extremely concentrated by weight; algae such as spirulina and the natural-source Dunaliella salina alga are commercial sources of mixed natural carotenes.

Maximizing absorption from food: always pair beta-carotene-rich vegetables with a source of fat — olive oil, avocado, nuts, or full-fat dairy. Light cooking (steaming, roasting, sauteing) and mechanical breakdown (chopping, blending) rupture the tough plant cell walls that otherwise trap the pigment. A salad of raw spinach delivers far less beta-carotene than the same spinach lightly wilted in olive oil; carrots eaten with a fat source can deliver several times the carotenoid of plain raw carrot sticks.

Whole-food beta-carotene comes packaged with alpha-carotene, beta-cryptoxanthin, lutein, zeaxanthin, fiber, potassium, and vitamin C — a synergistic matrix that isolated supplements cannot reproduce, and which underlies the consistent finding that dietary carotenoid intake tracks with better health even where supplements failed.

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Benefit: Eye Health & Vision

Beta-carotene's connection to eyesight is real but frequently misunderstood. The childhood claim that "carrots help you see in the dark" traces to a genuine biochemical truth wrapped in wartime propaganda: vitamin A (made from beta-carotene) is the essential precursor of rhodopsin, the light-sensitive pigment in the rod cells of the retina that enables night vision. The 11-cis-retinal derived from vitamin A combines with the protein opsin to form rhodopsin; when light strikes it, the retinal isomerizes and triggers the nerve signal of sight. Vitamin A deficiency is the world's leading cause of preventable childhood blindness, beginning with night blindness (nyctalopia) and progressing to xerophthalmia and corneal destruction. In a vitamin-A-deficient person, beta-carotene reverses night blindness; in a well-nourished person, extra beta-carotene does not give superhuman vision.

The more important modern role is in age-related macular degeneration (AMD), the leading cause of vision loss in older adults. The landmark Age-Related Eye Disease Study (AREDS, 2001), run by the U.S. National Eye Institute, showed that a high-dose antioxidant formula — vitamin C, vitamin E, zinc, copper, and 15 mg of beta-carotene — reduced progression to advanced AMD by about 25% over five years in people at high risk. The follow-up AREDS2 (2013) trial then replaced beta-carotene with the macular xanthophylls lutein and zeaxanthin, for two reasons: lutein/zeaxanthin are the carotenoids actually concentrated in the macula, and beta-carotene posed a lung-cancer risk in the trial's many former smokers. AREDS2 found lutein + zeaxanthin worked at least as well and was safer. As a result, modern AMD eye formulas have largely removed beta-carotene and substituted lutein and zeaxanthin — a direct, practical consequence of the smoker-safety data discussed below.

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Benefit: Skin Health & Photoprotection

Beta-carotene accumulates in the skin, where it serves a dual cosmetic and protective role. Because it is an orange-yellow pigment deposited in the fat of the dermis, a carotenoid-rich diet imparts a warm golden tone to the skin. Studies have shown this "carotenoid coloration" is perceived as healthier and more attractive than tanning from sun exposure — and unlike a UV tan, it carries no DNA damage. (At very high intake the harmless pigment can tint the palms and soles orange, a condition called carotenodermia, discussed under Cautions.)

More importantly, beta-carotene provides systemic photoprotection from the inside out. As the body's premier singlet-oxygen quencher, dermal beta-carotene neutralizes the reactive oxygen species generated when ultraviolet light strikes skin, reducing the lipid peroxidation, inflammation, and erythema (sunburn) that follow. Meta-analyses of controlled trials show that supplementation for at least 10–12 weeks meaningfully raises the minimal erythemal dose — the amount of UV needed to cause visible reddening — with longer supplementation producing larger effects. This is genuine but modest protection: it is the equivalent of a low sun-protection factor and is not a substitute for topical sunscreen. Combining beta-carotene with vitamin E enhances the effect.

Clinically, oral beta-carotene (often with canthaxanthin) has long been used to manage erythropoietic protoporphyria (EPP), a rare inherited disorder of extreme, painful photosensitivity, where it markedly increases sun tolerance. It is also studied in polymorphous light eruption ("sun allergy"). Beta-carotene is one of several carotenoids — alongside lycopene and the xanthophylls — that together form the skin's dietary antioxidant shield.

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Benefit: Immune Function

Beta-carotene supports immunity along two pathways. The first is indirect, through its role as a vitamin A precursor: vitamin A (as retinoic acid) is essential for the integrity of the epithelial barriers that form the body's first line of defense — the skin and the mucosal linings of the respiratory, digestive, and urinary tracts. Retinoic acid also drives the maturation and function of T-lymphocytes, regulates the balance of helper-T-cell subsets, supports antibody responses, and is critical for the gut-homing of immune cells. Vitamin A deficiency is one of the most important nutritional causes of impaired immunity worldwide, dramatically increasing childhood mortality from measles, diarrheal disease, and respiratory infection — the reason the World Health Organization runs global vitamin A supplementation programs in children.

The second pathway is direct: as a membrane antioxidant, beta-carotene protects immune cells — which generate large quantities of reactive oxygen species during the respiratory burst they use to kill pathogens — from oxidizing their own membranes. Some human studies report that beta-carotene supplementation enhances natural-killer-cell activity and lymphocyte proliferation, particularly in older adults whose immune function and tissue carotenoid levels have declined with age. The evidence here is suggestive rather than definitive, and the practical message is the familiar one: an immune benefit is reliably associated with adequate carotenoid intake from a varied diet, not with isolated megadoses.

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Benefit: Antioxidant Status & Lipid Protection

Plasma beta-carotene is one of the most-used biomarkers of overall fruit-and-vegetable intake and is a useful index of a person's lipid-phase antioxidant reserve. Within circulating lipoproteins, beta-carotene rides inside LDL and HDL particles, where — together with vitamin E and other carotenoids — it helps defend the polyunsaturated fatty acids of the lipoprotein from oxidation. Oxidation of LDL is an early, pivotal step in atherosclerotic plaque formation, so the carotenoids carried within LDL form part of the particle's built-in protection.

Large prospective cohort studies consistently show that people with the highest dietary intake and highest blood levels of beta-carotene have lower rates of cardiovascular disease, certain cancers, and all-cause mortality. This is the observational evidence that originally motivated the supplement trials. The crucial lesson of the past three decades, however, is that this association reflects the value of a carotenoid-rich diet — and everything that travels with it — rather than the isolated molecule. When researchers extracted beta-carotene, concentrated it into a pill, and gave it at supraphysiologic doses, the benefit not only disappeared but in high-risk groups reversed (next section). Beta-carotene's antioxidant contribution is best understood as one well-coordinated player in the body's redox network, alongside CoQ10, glutathione, and the vitamin C/E cycle — not as a stand-alone therapeutic agent to be megadosed.

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Benefit: Cognitive & Vascular Aging

The brain, with its high oxygen consumption and lipid-rich membranes, is particularly vulnerable to oxidative damage, and several lines of evidence link carotenoid status to cognitive aging. The Physicians' Health Study II included a sub-study in which men took beta-carotene (50 mg every other day) for an average of 18 years; those on long-term supplementation showed modestly better scores on tests of verbal memory and general cognition than the placebo group, whereas a separate short-term arm showed no effect — suggesting that any cognitive benefit, if real, requires many years to emerge. Observational studies similarly tie higher plasma carotenoids (beta-carotene, plus lutein and zeaxanthin) to slower cognitive decline and lower dementia risk.

As with cardiovascular outcomes, this is best read as supporting a lifelong carotenoid-rich dietary pattern rather than as an endorsement of high-dose supplements — especially given the safety signal in smokers. The most prudent strategy for protecting the aging brain and vasculature is a diet rich in colorful vegetables and fruit, which supplies beta-carotene within its natural matrix of cooperating antioxidants.

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The ATBC & CARET Trials: The Smoker Paradox

This is the most important section on the page, and the single most-cited cautionary tale in supplement science. By the late 1980s, observational data overwhelmingly suggested that people who ate more beta-carotene-rich foods, and who had higher blood beta-carotene, had less lung cancer. The logical hypothesis was that giving beta-carotene supplements to high-risk people — smokers — would lower their cancer risk. Two large randomized trials set out to prove it. Both produced the opposite result.

ATBC (Alpha-Tocopherol, Beta-Carotene) trial, 1994

Published in the New England Journal of Medicine, the ATBC Study (the ATBC Cancer Prevention Study Group, NEJM 1994) randomized 29,133 male smokers in Finland to beta-carotene (20 mg/day), vitamin E (alpha-tocopherol), both, or placebo, and followed them for 5–8 years. The result stunned the field: the men taking synthetic beta-carotene had an 18% higher incidence of lung cancer and an 8% higher overall mortality than those not taking it. The vitamin E arm showed no such harm. The trial that was designed to prove beta-carotene prevented lung cancer instead found it increased it.

CARET (Carotene and Retinol Efficacy Trial), 1996

Published two years later in the New England Journal of Medicine (Omenn and colleagues, NEJM 1996), CARET tested a combination of 30 mg/day beta-carotene plus 25,000 IU of retinyl palmitate (vitamin A) in 18,314 participants at high risk — current and former heavy smokers and asbestos-exposed workers. CARET was stopped early, about 21 months ahead of schedule, when the data confirmed ATBC: the supplement group had a 28% higher incidence of lung cancer and a 17% higher death rate. Independently, the U.S. Physicians' Health Study found beta-carotene neither helped nor harmed in a population that was largely non-smoking — reinforcing that the harm was specific to smokers and high-level carcinogen exposure.

Why isolated megadoses backfired in smokers

The leading biochemical explanations all converge on context-dependence:

• Pro-oxidant behavior at high oxygen tension. The lung has the highest oxygen partial pressure in the body, made worse by the oxidant load of cigarette smoke. Under these conditions, high concentrations of beta-carotene can flip from antioxidant to pro-oxidant, with its breakdown radicals propagating rather than quenching oxidative damage.
• Harmful oxidative cleavage products. Cigarette-smoke oxidants cleave beta-carotene into eccentric apocarotenal fragments that interfere with retinoic-acid signaling, disrupt normal cell-growth control, and can induce carcinogen-activating enzymes in lung tissue.
• Supraphysiologic dose. The 20–30 mg/day used was many times higher than is ever achievable from food, pushing tissue concentrations into a range the body's regulatory systems never evolved to handle.

The take-home message

The crucial distinction, repeated by every authoritative body since, is between the nutrient and the isolated megadose:

• Beta-carotene from food is safe and beneficial for everyone, including smokers. No study has ever found harm from dietary beta-carotene in carrots, sweet potatoes, squash, or leafy greens. The self-limiting biology and the protective food matrix prevent the pro-oxidant scenario.
• High-dose synthetic beta-carotene supplements should be avoided by current and former smokers and people with significant asbestos exposure. U.S. Preventive Services Task Force guidance specifically recommends against beta-carotene supplements for the prevention of cardiovascular disease or cancer, citing this harm signal.
• Eat the carrot; skip the high-dose pill. The episode is a textbook demonstration that an antioxidant beneficial in food can become harmful when extracted, concentrated, and consumed far outside its natural dose range and matrix — a lesson that reshaped how nutrition science evaluates single-nutrient supplementation.

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Dietary Intake & Supplement Dosing

There is no formal Recommended Dietary Allowance (RDA) for beta-carotene itself, because the body's need is for vitamin A, which can also be supplied as preformed retinol. There is likewise no Tolerable Upper Intake Level for beta-carotene from food — reflecting its food-source safety — although authorities caution explicitly against high-dose supplements in smokers.

• Dietary target (everyone) — obtain beta-carotene from food: aim for the equivalent of about 3–6 mg/day from a varied diet of orange, yellow, and dark-green vegetables and fruit. Several servings of carrots, sweet potato, squash, or leafy greens easily meet this, eaten with a little fat for absorption. This is the recommended approach for the overwhelming majority of people.
• Supplemental beta-carotene — when used, low doses in the range of roughly 3–6 mg/day (often expressed as 5,000–10,000 IU) are sometimes included in multivitamins as a vitamin-A source. Doses at this level have not shown the harms seen in the trials, but provide no demonstrated advantage over food for the general population.
• AREDS-type eye formulas — the original AREDS used 15 mg/day, but the modern AREDS2 formulation has replaced beta-carotene with lutein (10 mg) and zeaxanthin (2 mg) for both efficacy and smoker safety. Choose the beta-carotene-free formula.
• Clinical photosensitivity (EPP) — high therapeutic doses (often 30–180 mg/day) are used under specialist supervision for erythropoietic protoporphyria; this is a supervised medical use, not a consumer recommendation.
• Form — if supplementing, natural mixed carotenoids (e.g., from Dunaliella salina algae, supplying beta-carotene alongside alpha-carotene and other carotenoids) are generally preferred over isolated all-trans synthetic beta-carotene, as the synthetic single-isomer form is what was used in the harmful trials.

Bottom line: the optimal and safest dose of beta-carotene for nearly everyone is the amount delivered by a colorful, vegetable-rich diet. High-dose isolated supplements are not recommended for general use and are specifically contraindicated in smokers.

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Cautions and Contraindications

• Smokers and asbestos-exposed individuals — do not take high-dose supplements. Per the ATBC and CARET trials, current and former smokers and those with heavy asbestos exposure should avoid beta-carotene supplements above the small amounts found in a standard multivitamin. This is the single most important caution and applies regardless of how long ago one quit smoking, since former smokers were also harmed.
• Carotenodermia — very high beta-carotene intake (from food or supplements) can deposit pigment in the skin, turning the palms, soles, and nasolabial folds a harmless orange-yellow. Unlike jaundice it spares the whites of the eyes, is benign, and reverses over weeks once intake drops. It is a cosmetic sign of high intake, not a toxicity.
• Not a source of vitamin A toxicity — because conversion is self-regulated, beta-carotene cannot cause the headache, liver damage, or birth defects associated with excess preformed retinol. This makes it the safer provitamin-A choice in pregnancy, where high-dose retinol is teratogenic. Even so, pregnant and breastfeeding women should obtain beta-carotene from food and avoid high-dose isolated supplements.
• Drug and nutrient interactions — absorption is reduced by fat-blocking weight-loss drugs (orlistat), bile-acid sequestrants (cholestyramine, colestipol), and the cholesterol-absorption blocker ezetimibe. The combination of beta-carotene with a statin plus niacin blunted the HDL-raising and clinical benefit in one cardiovascular trial (HATS), an interaction worth noting for patients on lipid therapy.
• Heavy alcohol use — chronic high alcohol intake may worsen the pro-oxidant, liver-stressing potential of high-dose beta-carotene; another reason to favor food sources.
• General principle — the safety concerns attach almost entirely to isolated, high-dose supplements. Beta-carotene as it occurs in whole foods has an excellent safety record across all populations.

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Key Research Papers

The following are landmark peer-reviewed studies and authoritative references on beta-carotene. DOI and PubMed links open in a new tab.

1. The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The effect of vitamin E and beta carotene on the incidence of lung cancer and other cancers in male smokers. New England Journal of Medicine. 1994;330(15):1029–1035. DOI: 10.1056/NEJM199404143301501 · PMID: 8127329
2. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease (CARET). New England Journal of Medicine. 1996;334(18):1150–1155. DOI: 10.1056/NEJM199605023341802 · PMID: 8602180
3. Hennekens CH, Buring JE, Manson JE, et al. Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease (Physicians' Health Study). New England Journal of Medicine. 1996;334(18):1145–1149. DOI: 10.1056/NEJM199605023341801 · PMID: 8602179
4. Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration (AREDS Report No. 8). Archives of Ophthalmology. 2001;119(10):1417–1436. DOI: 10.1001/archopht.119.10.1417 · PMID: 11594942
5. Age-Related Eye Disease Study 2 (AREDS2) Research Group. Lutein + zeaxanthin and omega-3 fatty acids for age-related macular degeneration: the AREDS2 randomized clinical trial. JAMA. 2013;309(19):2005–2015. DOI: 10.1001/jama.2013.4997 · PMID: 23644932
6. Druesne-Pecollo N, Latino-Martel P, Norat T, et al. Beta-carotene supplementation and cancer risk: a systematic review and metaanalysis of randomized controlled trials. International Journal of Cancer. 2010;127(1):172–184. DOI: 10.1002/ijc.25008 · PMID: 19876916
7. Köpcke W, Krutmann J. Protection from sunburn with beta-carotene — a meta-analysis. Photochemistry and Photobiology. 2008;84(2):284–288. DOI: 10.1111/j.1751-1097.2007.00253.x · PMID: 18086246
8. Grodstein F, Kang JH, Glynn RJ, Cook NR, Gaziano JM. A randomized trial of beta carotene supplementation and cognitive function in men (Physicians' Health Study II). Archives of Internal Medicine. 2007;167(20):2184–2190. DOI: 10.1001/archinte.167.20.2184 · PMID: 18001195
9. von Lintig J. Provitamin A metabolism and functions in mammalian biology. American Journal of Clinical Nutrition. 2012;96(5):1234S–1244S. DOI: 10.3945/ajcn.112.034629 · PMID: 23053549
10. Lietz G, Lange J, Rimbach G. Molecular and dietary regulation of beta,beta-carotene 15,15'-monooxygenase 1 (BCMO1). Archives of Biochemistry and Biophysics. 2010;502(1):8–16. DOI: 10.1016/j.abb.2010.06.032 · PMID: 20599666
11. Burton GW, Ingold KU. Beta-carotene: an unusual type of lipid antioxidant. Science. 1984;224(4649):569–573. DOI: 10.1126/science.6710156 · PMID: 6710156
12. Mathews-Roth MM. Carotenoids in erythropoietic protoporphyria and other photosensitivity diseases. Annals of the New York Academy of Sciences. 1993;691:127–138. DOI: 10.1111/j.1749-6632.1993.tb26164.x · PMID: 8129277

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External Authoritative Resources

• Linus Pauling Institute — Vitamin A & Carotenoids Micronutrient Information Center
• NIH Office of Dietary Supplements — Vitamin A & Carotenoids Fact Sheet
• MedlinePlus — Beta-Carotene
• PubMed — All research on beta-carotene

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Connections

• All Antioxidants
• Astaxanthin
• CoQ10
• Glutathione
• Alpha Lipoic Acid
• Quercetin
• Spirulina
• Chlorella
• Vitamin A
• Vitamin C
• Vitamin E
• Sweet Potatoes
• Oxidative Stress
• Cadmium (Cigarette-Smoke Toxin)
• Eye Health & Vision
• Skin Health
• Zinc
• Selenium

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