Retinol comes from three places: animal foods that contain it ready-made, plant foods that your body converts into it, and chemical synthesis in factories that produce it for supplements and skincare. The form found in animal tissues is called preformed retinol because it requires no conversion. The form found in orange and dark-green vegetables is a precursor, beta-carotene, that your intestines must process before it becomes usable retinol.
Animal Foods With Preformed Retinol
Animals concentrate retinol in their livers, so organ meats are by far the richest natural source. A single cooked slice of beef liver (about 68 grams) contains roughly 6,410 micrograms of retinol, which is more than double the tolerable upper intake level of 3,000 micrograms per day. Cod liver oil is the next most concentrated source at about 1,350 micrograms per teaspoon, though some preparations run even higher, with one tablespoon delivering approximately 4,080 micrograms.
Everyday animal foods contain far less. A cup of whole milk provides about 110 micrograms, a large egg has 97, and a tablespoon of butter adds 95. Skim and reduced-fat milk are often fortified with vitamin A to replace what’s lost when the fat is removed. Nonfat milk with added vitamin A actually delivers slightly more retinol per cup (157 micrograms) than whole milk. Fortified breakfast cereals contribute about 230 micrograms per serving.
How Your Body Makes Retinol From Plants
Plants don’t contain retinol. What they contain are carotenoid pigments, most importantly beta-carotene, which gives carrots, sweet potatoes, and mangoes their orange color and is also abundant in dark leafy greens like spinach and kale. Your body splits beta-carotene molecules roughly in half to produce retinol, and this conversion happens predominantly in the small intestine.
The enzyme responsible for this splitting has a name that matters only because genetics can change how well it works. About 45% of people carry gene variants that reduce the enzyme’s activity. In some cases, a double mutation cuts its efficiency by 57%, making those individuals significantly worse at turning plant foods into usable vitamin A. These “poor converters” may get far less retinol from a plate of carrots than someone without those variants, which is one reason dietary guidelines can’t treat plant and animal vitamin A sources as interchangeable.
The conversion ratio reflects this inefficiency. Current guidelines say it takes 12 micrograms of beta-carotene from food to equal 1 microgram of preformed retinol. For beta-carotene taken as a supplement, the ratio is better: 2 micrograms of supplemental beta-carotene equals 1 microgram of retinol, because the purified form is absorbed more easily than beta-carotene trapped in plant cell walls.
How Synthetic Retinol Is Made
Nearly all the retinol in supplements, fortified foods, and skincare products is manufactured through chemical synthesis. The process starts with petroleum-derived raw materials, specifically acetone and acetylene, which are combined to build a molecule called beta-ionone. This compound is the essential starting point for all industrial vitamin A production.
The route from beta-ionone to finished retinol involves assembling a chain of carbon atoms in a precise arrangement. BASF patented the first commercial process in 1956, using a reaction that joined a 15-carbon fragment to a 5-carbon fragment. In 1971, the French chemical company Rhône-Poulenc (now Adisseo) developed an alternative method using sulfone chemistry to form the critical carbon-carbon bonds. Both approaches remain the basis of modern production, with refinements to catalysts and reaction conditions improving yields over the decades.
The synthetic retinol molecule is chemically identical to the retinol found in beef liver or cod liver oil. Your body processes it the same way regardless of whether it was extracted from an animal source or assembled in a reactor.
Forms of Retinol in Products
Pure retinol is unstable. It breaks down when exposed to light, heat, and oxygen. For this reason, most supplements and skincare products use retinyl palmitate or retinyl acetate, which are retinol molecules bonded to a fatty acid for stability. When you apply retinyl palmitate to your skin or swallow it in a capsule, enzymes called lipases break the bond, releasing free retinol and a fatty acid (palmitic acid, in the case of retinyl palmitate).
This extra conversion step means retinyl esters are somewhat less potent than pure retinol at any given concentration. In skincare, this translates to a gentler but slower-acting product. In supplements, the conversion happens efficiently enough in the gut that the difference is minor for most people.
Why the Source Matters Nutritionally
Because plant-based beta-carotene requires conversion and that conversion varies dramatically between individuals, preformed retinol from animal foods or supplements is the more reliable way to meet vitamin A needs. This distinction is especially relevant for vegans, young children, and people with fat absorption disorders, all of whom may struggle to get enough retinol from plant sources alone.
On the other hand, preformed retinol is one of the few vitamins where toxicity from food is a real concern. That single slice of beef liver exceeds the safe upper limit. Cod liver oil can do the same at modest doses. Beta-carotene from plants carries no toxicity risk because the body slows its conversion when vitamin A stores are sufficient. The worst that happens with excess beta-carotene is a harmless orange tint to the skin, which fades when intake drops.
The recommended daily intake for adults is 900 micrograms for men and 700 micrograms for women, measured in retinol activity equivalents. A balanced diet that includes some dairy, eggs, or fortified foods alongside colorful vegetables will typically cover this without supplementation.