BAKERSFIELD, Calif. -- A young woman's chance of having a stroke is directly related to the number of cigarettes she smokes, according to new research.

Neurologists from the University of Maryland examined strokes in younger women, ages 15 to 49, and found that any smoking doubled the odds of stroke.

But the more cigarettes women smoked per day, the higher their risk climbed. Young women who smoked one to 10 cigarettes per day had more than twice the stroke risk of nonsmokers, but those who smoked 40 or more cigarettes per day increased their odds of stroke by more than nine times.

Researchers said smoking raises stroke risk in several ways: it increases the stickiness of blood cells and makes them more likely to clot, and at the same time weakens the body's own mechanism for dissolving the clots.