How vitamin K helps prevent hemorrhaging.

Vitamin K, the blood-clotting vitamin, bears that nickname for good reason. A deficiency of this naturally occurring nutrient, though rare in well-fed societies, can cause hemorrhaging.

This observation prompts pediatricians to give newborns a healthy shot of vitamin K to lower the 1 percent risk of spontaneous bleeding they would otherwise face.

How does vitamin K work?

Until recently, no one has been quite certain. Now, researchers explain how the nutrient helps blood clot normally.

Paul Dowd, a chemist at the University of Pittsburgh, and his colleagues describe how an energy transfer mechanism in vitamin K enables it to trigger coagulation. In the Sept. 22 Science, Dowd's group details the vitamin's use of oxygen and carbon dioxide to liberate energy that, in turn, affects clot-inducing proteins, setting in motion a "blood-clotting cascade."

"Since vitamin K lies at the heart of blood coagulation, which heals injuries but also causes heart attacks and strokes," Dowd says, "the key question is: How can someone preserve the blood's injury-healing abilities yet stop unwanted internal clots?

"That question drives most of the research into vitamin K's biochemistry."

Since the discovery of vitamin K in 1929, researchers have sought a deeper understanding of its chemical mechanisms in order to further its clinical use, says Robert E. Olson, a biochemist at the University of South Florida in Tampa. Vitamin K, one of four fat-soluble vitamins, is essential to human health.

"We knew that oxygen combined with vitamin K, but we weren't sure exactly how," Olson says. "That's what Dowd has now clarified."