History
In 1929 Denmark's Henrik Dam found that chicks fed fat-free feed bled easily, and in 1935 he named the missing factor vitamin K after the German Koagulation. Edward Doisy in the US determined its structure, and the two shared the 1943 Nobel Prize. In the 1940s Wisconsin researchers traced cattle deaths from spoiled sweet clover to dicoumarol, which blocks vitamin K; it led to warfarin, first a rat poison and then an anticoagulant drug.
What it does and where it is found
The liver uses vitamin K to make clotting factors such as prothrombin, and in bone it activates osteocalcin, which helps bind calcium. K1 (phylloquinone) comes from spinach, kale, broccoli and lettuce; K2 (menaquinones) from natto, cheese and gut bacteria. It is absorbed better with fat. Deficiency is rare in healthy adults but can follow fat malabsorption or long antibiotic courses.
Warfarin and newborns
Warfarin works by blocking vitamin K, so users need not avoid vegetables but should keep intake steady rather than changing it suddenly; discuss natto, green juices and supplements with a doctor. Newborns receive little through the placenta and lack gut bacteria, so since the American Academy of Pediatrics' 1961 recommendation a vitamin K injection at birth has been standard. Evidence that K2 supplements prevent fractures remains mixed.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Must I avoid vegetables on warfarin?
- No—eat a similar amount consistently each day.
- Is the newborn vitamin K shot necessary?
- Yes—it is recommended worldwide to prevent rare but deadly brain bleeds.
Sources reviewed: 2026-10-26
References
- Dam, H. (1935). The antihaemorrhagic vitamin of the chick. Biochemical Journal, 29(6), 1273–1285.
- American Academy of Pediatrics Committee on Fetus and Newborn. (2003). Controversies concerning vitamin K and the newborn. Pediatrics, 112(1), 191–192.
- Institute of Medicine. (2001). Dietary Reference Intakes: Vitamin K. National Academies Press.