Who Found Vitamin K, and How a Clotting Vitamin Became the K2 Story

Vitamin K started with chicks that bled on a synthetic diet. Henrik Dam named the factor in 1935, and he and Edward Doisy shared the 1943 Nobel Prize. The later story is the K2 family, the MK-7 trials, and a warning for people on warfarin.

The history of vitamin K starts with chicks that bled. Henrik Dam was studying sterol metabolism when his chickens, fed a low-fat synthetic diet, began to bleed internally in a way that looked like scurvy. Vitamin C did not reverse it, so the bleeding pointed to a factor nobody had named yet ([NobelPrize.org, Dam](https://www.nobelprize.org/prizes/medicine/1943/dam/facts/); [Norn et al., 2014](https://pubmed.ncbi.nlm.nih.gov/25639072/)). ## Why is vitamin K named for blood clotting? In 1934 Dam showed that adding hempseed counteracted the bleeding. He concluded that the seed held a substance the blood needs to coagulate, and he called that substance vitamin K ([NobelPrize.org, Dam](https://www.nobelprize.org/prizes/medicine/1943/dam/facts/)). According to PubMed, the unknown factor was named vitamin K in 1935, and a few months later H.J. Almquist and E.L.R. Stokstad in Berkeley observed the same phenomenon ([Norn et al., 2014](https://pubmed.ncbi.nlm.nih.gov/25639072/)). For the scurvy side of that comparison, the [history of vitamin C](/blog/history/history-of-vitamin-c-from-scurvy-to-ascorbic-acid) is the place to start. ## Who shared the Nobel Prize for vitamin K? Henrik Dam and Edward Adelbert Doisy shared the 1943 Nobel Prize in Physiology or Medicine, each taking half. Dam was honored "for his discovery of vitamin K," and Doisy "for his discovery of the chemical nature of vitamin K" ([NobelPrize.org, Dam](https://www.nobelprize.org/prizes/medicine/1943/dam/facts/); [NobelPrize.org, Doisy](https://www.nobelprize.org/prizes/medicine/1943/doisy/facts/)). Both received their prizes a year later, in 1944. Doisy's work was chemical. In 1939 he produced two variants of vitamin K in pure form, which let him determine its structure and make the vitamin by artificial means. That became especially important in treating bleeding among small children ([NobelPrize.org, Doisy](https://www.nobelprize.org/prizes/medicine/1943/doisy/facts/)). According to PubMed, a Danish medical history credits Dam and Paul Karrer with isolating vitamin K in Zurich in 1939, and credits Doisy with determining its structure ([Norn et al., 2014](https://pubmed.ncbi.nlm.nih.gov/25639072/)). ## What is the difference between K1 and K2? Vitamin K1 is phylloquinone, the form found in plant foods. Vitamin K2 is the menaquinone family, and gut bacteria produce some of it. The NIH says research indicates that substantial quantities of long-chain menaquinones are present in the large bowel, and that experts believe they satisfy at least some of the body's requirement. How much the body absorbs from that source is unclear ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/)). Supplements carry K1 as phylloquinone or phytonadione, a synthetic form of K1, and K2 as MK-4 or MK-7. Food composition tables report most vitamin K as phylloquinone because menaquinone data are limited ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/)). Menadione, sometimes called vitamin K3, is another synthetic form. The NIH says lab studies in the 1980s and 1990s showed it damaged liver cells, so it is no longer used in dietary supplements or fortified foods ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/)). For the forms and doses of K2 in more detail, see the [vitamin K2 monograph](/ingredients/vitamin-k2). ## How did natto get into the K2 research? The MK-7 in the 2007 comparison was derived from natto. Schurgers and colleagues tested synthetic vitamin K1 against natto-derived menaquinone-7 in healthy volunteers ([Schurgers et al., 2007](https://doi.org/10.1182/blood-2006-08-040709)). According to PubMed, both forms were absorbed well, with peak serum concentrations at 4 hours. MK-7 had a much longer half-life, which gave steadier serum levels and built up to 7 to 8 times higher levels during prolonged intake. It also induced more complete carboxylation of osteocalcin. The NIH food table lists 850 micrograms of MK-7 in a 3-ounce serving of natto ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/)). ## What did the bone and blood vessel studies test? The bone trial gave 244 healthy postmenopausal women either placebo or 180 mcg of MK-7 a day for three years ([Knapen et al., 2013](https://doi.org/10.1007/s00198-013-2325-6)). MK-7 improved vitamin K status and reduced the age-related decline in bone mineral content and density at the lumbar spine and femoral neck, but not at the total hip. It also favorably affected bone strength and reduced the loss of vertebral height in the lower thoracic region. The authors said that whether the results extend to children and men needs further investigation. A second three-year trial used the same 180 mcg dose in 244 healthy postmenopausal women, 120 on MK-7 and 124 on placebo, and measured arterial stiffness. After three years, MK-7 significantly decreased carotid-femoral pulse wave velocity and the Stiffness Index beta in the whole group. In women whose baseline Stiffness Index beta was above the median, several local carotid measures improved too. MK-7 lowered circulating dp-ucMGP by 50 percent compared with placebo, but did not change the acute-phase or endothelial markers that were measured ([Knapen et al., 2015](https://doi.org/10.1160/TH14-08-0675)). The [vitamin D complete guide](/health/vitamin-d-complete-guide) covers the vitamin D side of this pairing, and the [D3 and K2 combination article](/health/vitamin-d-complete-guide/vitamin-d3-k2-combination-benefits) looks at the two together. Two Mt. Angel Vitamins products carry 120 mcg of K2 as MK-7 per serving, which is below the 180 mcg used in those trials. [Everyday Liquid Sunshine 2 D3 + K2](https://mtangelvitamins.com/products/everyday-liquid-sunshine-2-d3-k2?utm_source=learn_hub&utm_medium=content&utm_campaign=blog_post&utm_content=history-of-vitamin-k-from-danish-blood-clotting-to-k2) puts 5,000 IU of vitamin D3 and 120 mcg of K2 in one dropper squeeze, about 70 servings per 2 fl oz bottle at $25.99, or about 37 cents a day. [Bones + K2 with Aquamin Calcium](https://mtangelvitamins.com/products/bones-k2-comprehensive-bone-supp?utm_source=learn_hub&utm_medium=content&utm_campaign=blog_post&utm_content=history-of-vitamin-k-from-danish-blood-clotting-to-k2) provides 500 mg of calcium from red algae, 25 mcg of D3 and 120 mcg of K2 as MK-7 in two capsules, 30 servings for $27.99, or about 93 cents a day. Vitamin K2 helps activate osteocalcin, a bone protein.† *†These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.* ## Why does vitamin K matter for people taking blood thinners? Vitamin K can have a serious and potentially dangerous interaction with warfarin (Coumadin) and similar anticoagulants. These drugs work against vitamin K, so people who take them need a consistent intake from food and supplements, because sudden changes can raise or lower the anticoagulant effect ([NIH ODS](https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/)). The NIH advises anyone who takes these medicines regularly to discuss their vitamin K status with their health care providers. The 2007 Blood paper gave hematologists a specific warning: preparations supplying 50 mcg a day or more of MK-7 may interfere with oral anticoagulant treatment in a clinically relevant way ([Schurgers et al., 2007](https://doi.org/10.1182/blood-2006-08-040709)). Warfarin has an older story. Norn and colleagues describe cattle in Canada dying of internal bleeding in the 1920s, and a veterinary pathologist in Alberta traced the mysterious disease to spoiled sweet clover hay. A farmer once traveled through a blizzard with a dead cow and a milk can of unclotted blood to the University of Wisconsin, where, by their account, only the door to Karl Paul Link's biochemistry department was open. That visit started the isolation of dicoumarol. Warfarin was first used as an effective rat poison, and it later became the drug of choice for thromboembolic diseases ([Norn et al., 2014](https://pubmed.ncbi.nlm.nih.gov/25639072/)). Dam's chicks were a lucky choice, according to the Danish account, because the vitamin is not formed by intestinal bacteria in chicks. In people, the large bowel holds substantial quantities of long-chain menaquinones, and the NIH says how much of that the body absorbs is still unclear. **Next reads** - [Vitamin K2 monograph](/ingredients/vitamin-k2): the reference page for K2 forms and doses. - [History of vitamin C, from scurvy to ascorbic acid](/blog/history/history-of-vitamin-c-from-scurvy-to-ascorbic-acid): the scurvy story that Dam's chicks were compared with. ### Related reading - [The history of vitamin D from rickets to the sunshine vitamin](/blog/history/history-of-vitamin-d-from-rickets-to-sunshine-vitamin) - [The history of vitamin E](/blog/history/history-of-vitamin-e-from-fertility-factor-to-tocopherol)