Vitamin A

What It Does

Retinal is the light-absorbing molecule in rhodopsin, and its absence first shows up as night blindness. Retinoic acid binds nuclear receptors (RAR and RXR) that control the transcription of hundreds of genes involved in cell differentiation, epithelial maintenance, immunity, and embryonic development. Worldwide, deficiency remains a leading cause of preventable childhood blindness and worsens the course of measles.

Beta-carotene is split into retinal by the enzyme BCMO1 in the intestinal wall, and the body slows that conversion when vitamin A status is adequate. On average it takes 12 mcg of beta-carotene from food, or 2 mcg from a supplement in oil, to yield 1 mcg of retinol. The average hides wide variation. Two common BCMO1 variants reduced conversion by up to about 70% in carriers (Leung 2009), which matters for vegans who rely entirely on carotenoids.

Preformed vitamin A has a narrow margin. The UL is 3,000 mcg RAE (10,000 IU) a day. Chronic excess causes liver damage and raised intracranial pressure, and higher retinol intakes have been linked to lower bone density and more hip fractures in Swedish and US cohorts (Melhus 1998, Feskanich 2002). In pregnancy, women taking more than 10,000 IU a day of preformed vitamin A from supplements had a higher rate of birth defects involving the head and heart (Rothman 1995). Isotretinoin and acitretin are vitamin A derivatives with the same teratogenic risk.

Beta-carotene is not harmless in supplement doses. In the ATBC trial, 29,133 Finnish male smokers taking 20 mg of beta-carotene daily had 18% more lung cancer (ATBC 1994). In CARET, 30 mg of beta-carotene plus 25,000 IU of retinyl palmitate in smokers and asbestos-exposed workers raised lung cancer by 28%, and the trial was stopped early (Omenn 1996).

Forms and Bioavailability

Absorption ratings are broad tiers. Head-to-head human trials rarely support a finer ranking among well-absorbed forms.

Labels column: number of labels named as vitamin A products that list this form. A product can list more than one form, and some labels do not state a form at all.

Retinyl palmitate and retinyl acetate are interchangeable preformed vitamin A and count fully toward the UL. Beta-carotene does not count toward the UL. Labels since 2020 state vitamin A in mcg RAE; older labels in IU. One IU of retinol equals 0.3 mcg RAE, and one IU of supplemental beta-carotene equals 0.15 mcg RAE. Many multivitamins split their vitamin A between the two forms and state the percentage from beta-carotene.

Typical Dosing

Since 2020, US labels state vitamin A in mcg RAE. 1 mcg RAE equals 1 mcg retinol, 2 mcg of beta-carotene from a supplement, or 12 mcg of beta-carotene from food.

Food sources: beef liver, cod liver oil, sweet potato, spinach, carrots, pumpkin, cantaloupe, eggs.

What to Look For

Check which form your multivitamin uses. For most adults, a product that supplies vitamin A mostly or entirely as beta-carotene, at a few milligrams, is the safer choice. Anyone who is or could become pregnant should keep preformed vitamin A from all supplements well under 3,000 mcg RAE, and limit liver and cod liver oil, since 3 ounces of beef liver alone exceeds the UL.

Smokers and former smokers should avoid beta-carotene at 20 mg or more. Standalone retinol supplements belong to documented deficiency, usually from fat malabsorption, under a clinician's care.

Red flags: 10,000 IU retinyl palmitate softgels taken daily for skin or immunity, cod liver oil stacked on a multivitamin with preformed vitamin A, and any vitamin A product combined with isotretinoin. Green flags: form stated, mcg RAE per serving, and the share from beta-carotene shown.

Products on Titrate

22,923 of the 214,745 labels in the NIH Dietary Supplement Label Database list vitamin A as an active ingredient (11,203 on market). 670 are sold as vitamin A products by name.

Top on-market labels, ranked by label completeness and simplicity:

1. Vitamin A 10,000 IU (3,000 mcg RAE) Carlson · 3 mg as retinyl palmitate
2. Beta-Carotene Herbadiet · 25000 IU as beta-carotene
3. Shark Liver Oil Vitamin A NOW · 10000 IU as retinyl palmitate
4. Vitamin A & D for Kids Nature's Nutra · 360 mcg as retinyl palmitate
5. Vitamin ADK Thyroid Formula Forefront Health · 5000 IU as retinyl palmitate

Open supplement search

Vitamin A does not have its own search category yet. Each product above links to its full label in the NIH database.

Related Tools

• Beta-Carotene vs Retinyl Palmitate
• All vitamin A form comparisons
• All supplement guides

References

NIH Office of Dietary Supplements. Vitamin A and Carotenoids: Fact Sheet for Health Professionals.

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. N Engl J Med. 1994;330(15):1029-1035.

Rothman KJ, Moore LL, Singer MR, Nguyen US, Mannino S, Milunsky A. Teratogenicity of high vitamin A intake. N Engl J Med. 1995;333(21):1369-1373.

Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Engl J Med. 1996;334(18):1150-1155.

Melhus H, Michaëlsson K, Kindmark A, et al. Excessive dietary intake of vitamin A is associated with reduced bone mineral density and increased risk for hip fracture. Ann Intern Med. 1998;129(10):770-778.

Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin A intake and hip fractures among postmenopausal women. JAMA. 2002;287(1):47-54.

Leung WC, Hessel S, Méplan C, et al. Two common single nucleotide polymorphisms in the gene encoding beta-carotene 15,15'-monoxygenase alter beta-carotene metabolism in female volunteers. FASEB J. 2009;23(4):1041-1053.