For the first time, researchers have linked the hardening of arteries to blood clots in veins, a finding that could trigger new research in the effort to prevent the blockages that kill thousands of people each year.

Italian researchers found patients hospitalized with unexplained deep-vein clots were nearly 2 1/2 times more likely to also have hardening of the arteries, or atherosclerosis, than patients with deep-vein clots attributed to other health problems. The doctors concluded either hardening of the arteries can induce blood clots in veins or the two conditions share common risk factors.

“I favor the first hypothesis,” said Dr. Paolo Prandoni, the lead researcher and an associate professor of internal medicine at the University of Padua Medical School.

Prandoni said scientists had not suspected the link. He said researchers now should study mechanisms that might connect artery and vein disorders, and whether cholesterol-lowering or anticlotting drugs can prevent deep-vein clots as well as control atherosclerosis to prevent heart attacks and strokes.

The study is in today’s edition of the New England Journal of Medicine.

Arteries, which carry blood from the heart throughout the body, can harden over time from factors including smoking, high blood pressure and cholesterol, or plaque, which stays in arteries and attaches to their walls.

Veins, which have thinner walls, don’t harden or build up plaque. But blood clots can form in veins from surgery, cancer, leg injury or immobilization, pregnancy, recent childbirth or use of the hormone estrogen. In about one-third of patients with a vein clot, there’s no identifiable reason — and thus no way to prevent it.

If part of a clot breaks free, it can travel to the lungs and lodge there, causing a blockage called a pulmonary embolism. Pulmonary embolisms kill at least 60,000 Americans annually, according to the Centers for Disease Control and Prevention; one apparently killed NBC war correspondent David Bloom on Sunday.