Who Found Vitamin A, and How Night Blindness Became a Supplement Story
More than 2,900 years before vitamin A was crystallized in 1937, Egyptian physicians prescribed ox liver for blindness. This is how a liver remedy became a measured fat-soluble nutrient, and where today's intake limits come from.
The history of vitamin A starts with a liver. Egyptian physicians prescribed ox liver for blindness in the second millennium BCE, more than 2,900 years before Holmes and Corbet crystallized the vitamin in 1937. The idea that liver helps night vision is far older than any measurement of vitamin A, and it took the 20th century to explain why it worked. ## How old is the idea that liver helps night vision? The oldest written prescriptions come from Egypt. The Papyrus Ebers and the London Medical Papyrus, both from the second millennium BCE, contain remedies for blindness, and the Egyptian version used ox liver. The liver was roasted or smoked, and its fluid was sprayed into the eyes of the sufferer. The prescriptions are short, but they draw a direct line between blindness and liver as medicine ([Panayotov, Nineveh Medical Project, British Museum](https://oracc.museum.upenn.edu/asbp/ninmed/historyofmedicine/liverforblindness/index.html)). The motif spread. Assyrian physicians favored donkey liver for day or night blindness. Hippocrates recorded a version in the Treatise on the Eye in the 5th century BCE, where the patient drank raw bull's liver dipped in honey. Dioscorides and Celsus, both writing in the 1st century CE, kept the idea alive with goat liver ([Nineveh Medical Project](https://oracc.museum.upenn.edu/asbp/ninmed/historyofmedicine/liverforblindness/index.html)). Assyriologist Marten Stol offered the modern explanation. Night blindness is a deficiency of vitamin A, and liver contains a large amount of it, which is why the liver remedy was probably so effective ([Nineveh Medical Project](https://oracc.museum.upenn.edu/asbp/ninmed/historyofmedicine/liverforblindness/index.html)). ## Who connected night blindness to diet? The sources I could verify do not name one person for that link. Liver was prescribed for centuries before the diet experiments that the historical review describes. The [historical review by Semba](https://doi.org/10.1159/000343124) opens the chain with François Magendie's 1816 deprivation experiments on dogs, which produced corneal ulcers and high mortality. The chain then moved in steps. Nicolai Lunin showed in the 1880s that milk held an unknown essential substance. Frederick Gowland Hopkins proposed "unsuspected dietetic factors" in 1906, and Wilhelm Stepp showed in 1911 that the milk factor was fat soluble. In 1913, Elmer McCollum and Marguerite Davis at Wisconsin, and Thomas Osborne and Lafayette Mendel at Yale, found that butter and egg yolk were not nutritionally equivalent to lard and olive oil for rat growth and survival. The factor became "fat-soluble A" in 1918 and "vitamin A" in 1920 ([Semba, 2012](https://doi.org/10.1159/000343124)). Fat solubility has a consequence. Because vitamin A is fat soluble, the body stores the excess, primarily in the liver, and those levels can accumulate, according to the [NIH Office of Dietary Supplements](https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/). Liver also appears as a clinical treatment in the [vitamin B12 origin story](/blog/history/history-of-vitamin-b12-from-liver-cure-to-cobalamin). ## When did researchers first isolate vitamin A? The answer has two steps. In 1931, Paul Karrer extracted vitamin A from cod-liver oil and determined its composition, according to the [Nobel Prize site](https://www.nobelprize.org/prizes/chemistry/1937/karrer/facts/). Karrer shared the 1937 chemistry prize for his work on carotenoids, flavins and vitamins A and B2. Holmes and Corbet crystallized vitamin A in 1937 ([Semba, 2012](https://doi.org/10.1159/000343124)). The cod-liver source has its own story in the [omega-3 history](/blog/history/history-of-omega-3-from-cod-liver-oil-to-epa-and-dha). The eye chapter closed in 1967. The Nobel Prize in Physiology or Medicine went to Ragnar Granit, Haldan Hartline and George Wald "for their discoveries concerning the primary physiological and chemical visual processes in the eye" ([Nobel Prize](https://www.nobelprize.org/prizes/medicine/1967/summary/)). Wald found that vitamin A is an important component in rhodopsin, a light-sensitive substance in the retina ([Nobel Prize, Wald facts](https://www.nobelprize.org/prizes/medicine/1967/wald/facts/)). ## What is the difference between retinol and beta-carotene? Retinol is the preformed form, the vitamin itself, and it comes from animal foods. Beta-carotene is a provitamin, a plant pigment the body converts into retinol. The [NIH Office of Dietary Supplements](https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/) measures both in retinol activity equivalents (RAE). One microgram RAE equals 1 mcg of retinol, 2 mcg of supplemental beta-carotene, or 12 mcg of dietary beta-carotene. The two forms also absorb differently. The body absorbs up to 75% to 100% of retinol from food, and in most cases 10% to 30% of beta-carotene from food. Preformed vitamin A supplies about 65% to 80% of intake in the United States and other high-income countries, while provitamin A is the main form in low-income countries with more plant-based diets. ### Where does supplemental vitamin A come from today? Supplements often list retinyl acetate or retinyl palmitate, which are preformed retinyl esters, or beta-carotene, or a mix of the two. The Office of Dietary Supplements notes that 3,000 mcg RAE is a common amount in supplements, while multivitamins commonly carry 750 to 1,050 mcg RAE ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/)). ## What did the beta-carotene trials find? Provitamin A has a harder chapter. The Beta-Carotene and Retinol Efficacy Trial (CARET) enrolled 18,314 people at high risk of lung cancer because of smoking or asbestos exposure. Participants took 30 mg of beta-carotene and 25,000 IU of retinyl palmitate daily. The trial stopped early in January 1996, because the active group had a 28% higher incidence of lung cancer and a 17% higher incidence of death than the placebo group ([Goodman et al., 2004](https://doi.org/10.1093/jnci/djh320)). After the supplements stopped, the lung cancer and mortality risk ratios stayed above 1.0, though they were no longer statistically significant. Among nonsmokers, the Office of Dietary Supplements reports that beta-carotene and vitamin A supplements do not appear to affect cancer risk ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/)). The eye trials pointed in a different direction for a different group. The Age-Related Eye Disease Study enrolled 3,640 adults aged 55 to 80 and tested antioxidants, with and without zinc. Antioxidants plus zinc lowered the odds of developing advanced age-related macular degeneration in the full cohort (odds ratio 0.72, 99% CI 0.52 to 0.98). The trial found no statistically significant serious adverse effect for any formulation ([AREDS report no. 8, 2001](https://doi.org/10.1001/archopht.119.10.1417)). The zinc in that formula is covered in the [zinc monograph](/ingredients/zinc). ## How much preformed vitamin A is too much? The Food and Nutrition Board's Tolerable Upper Intake Level for preformed vitamin A is 3,000 mcg a day for adults 19 and older. The figure is the same for men, women, pregnant women and lactating women. For ages 14 to 18 it is 2,800 mcg. The limit applies to food and supplements together ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/)). The Office of Dietary Supplements says the limits were set around increased risk of liver abnormalities, teratogenic effects (birth defects), and several toxic effects in infants and children. Chronic high intake can cause dry skin, painful muscles and joints, fatigue, depression and abnormal liver test results. No limit has been set for beta-carotene, and the board advises against beta-carotene supplements for the general population, except as a provitamin A source to prevent deficiency. The Egyptian remedy and Karrer's 1931 extract had the same starting point: liver, the organ where the body keeps most of its vitamin A. **Next reads** - [Vitamin D complete guide](/health/vitamin-d-complete-guide): the reference page for vitamin D, with dosage and food source guides. - [Vitamin C origin story](/blog/history/history-of-vitamin-c-from-scurvy-to-ascorbic-acid): another vitamin, another deficiency disease, and a different route to the name. ### Related reading - [the vitamin D origin story from rickets to sunshine](/blog/history/history-of-vitamin-d-from-rickets-to-sunshine-vitamin)