Younger women who smoke have more than double the risk of stroke compared to nonsmokers, with the heaviest smokers among them having nine times the risk, according to a U.S. study published on Thursday.

The research assessed stroke risk in women 15 to 49 years old who smoked cigarettes. Current smokers were 2.6 times as likely to have a stroke than women who had never smoked, according to researchers led by Dr. John Cole of the University of Maryland School of Medicine in Baltimore.

Women who smoked the most faced the highest risk, said the study, published in the American Heart Association’s journal Stroke.

For example, women who smoked 21 to 39 cigarettes a day had a risk of stroke 4.3 times higher than a nonsmoker, while those who puffed at least two packs a day - 40 cigarettes - had a stroke risk 9.1 times higher than a nonsmoker.

It has been known for a long time that smoking increases the risk of stroke, along with many other health dangers such as lung and other types of cancer, lung disease and heart disease.

But Cole said less was known about how stroke risk is affected by the number of cigarettes a person smokes.

Strokes typically occur in people older than this study population, but the research demonstrated that, even in younger women, stroke risk is greatly increased.

“The more you smoke, the more likely you are to have a stroke,” Cole said in a telephone interview. “Certainly quitting is the best thing you could do. But cutting back does offer some benefit.”

The researchers tracked 466 women in the United States who had already had a stroke and 604 women who had not had a stroke who were of similar age, race and ethnicity.

About a fifth of U.S. women ages 18 to 24 are current smokers, the researchers said.

Cole said he is planning a similar study focusing on stroke risk in younger male smokers.

By Will Dunham

WASHINGTON (Reuters)