Vitamin K is a fat-soluble vitamin that activates blood-clotting factors. In 1929 Dam reported that chickens fed a fat-extracted diet developed spontaneous fatal bleeding. Supplementation experiments showed that an unknown factor was indispensable for hepatic prothrombin synthesis. At the time vitamins A and D were known, but the idea of a vitamin functioning as a co-enzyme in a specific biochemical pathway was novel. Dam’s findings influenced surgical practice and the prevention of neonatal hemorrhage during World War II. Because drugs like warfarin inhibit the vitamin K cycle, his work also laid the biochemical foundation of modern anticoagulant therapy.

Vitamin K is a fat-soluble naphthoquinone that serves as a co-factor for γ-glutamyl carboxylase, the enzyme that converts specific glutamate residues in prothrombin and factors VII, IX and X into γ-carboxyglutamate (Gla). The critical insight in Dam’s work was that removing lipids from poultry feed inadvertently eliminated vitamin K as well as other pigments. He observed that adding alfalfa meal or fish flour restored clotting ability, revealing a lipid-soluble factor. Subsequent studies showed that vitamin K cycles between hydroquinone and epoxide forms in liver microsomes, acting as an electron carrier during carboxylation. This vitamin K cycle is blocked by warfarin, leading to under-carboxylated (inactive) coagulation proteins. Dam’s discovery propelled the molecular understanding of congenital coagulation disorders such as prothrombin deficiency. Later it became clear that osteocalcin produced by osteoblasts also requires vitamin K-dependent Gla residues, extending impact to bone metabolism. The cross-disciplinary influence on nutrition, biochemistry and clinical medicine justifies the Nobel recognition.

Working with a lipid-deficient diet model, Dam quantitatively demonstrated markedly prolonged prothrombin times and reduced hepatic prothrombin content. Active fractions from alfalfa extracts were tracked with acetone/petroleum-ether partitioning; UV spectra hinted at a naphthoquinone core although purification limits remained. His observations anticipated a quinone-based redox cofactor cycle later corroborated by Stenflo and colleagues in the Gla-carboxylation mechanism. The hemorrhagic phenotype paralleled that of warfarin-treated rat models, leading to identification of vitamin K epoxide reductase (VKORC1) as the pharmacological target. Dam’s data are still cited as early evidence for the Gla-domain paradigm explaining calcium-dependent membrane association in the coagulation cascade. Recent interest in vitamin K2-mediated osteoblast signaling and Gla-rich protein inhibition of vascular calcification underscores the transformative reach of his discovery. Thus his contribution is valued for inaugurating the concept of quinone cofactors driving post-translational modifications.