Atlanta ? Quitting smoking can turn back time.

A year after kicking the habit, smokers’ arteries showed signs of reversing a problem that can set the stage for heart disease, according to the first big study to test this.

The improvement came even though smokers gained an average of 9 pounds after they quit, researchers found. Their levels of so-called good cholesterol improved, too.

“A lot of people are afraid to quit smoking because they’re afraid to gain weight,” said the study’s leader, Dr. James Stein, a University of Wisconsin-Madison cardiologist.

Smoking is one of the top causes of heart disease, and about one third of smoking-related deaths in the U.S. are due to heart disease. A heart attack often motivates longtime smokers to give it up.

Quitting is known to lower the risk of developing or dying of lung cancer. This is the first major clinical trial to show it quickly improves artery health. Results were published in the Journal of the American College of Cardiology and presented at the group’s annual conference on Monday.

Doctors found that artery function improved 1 percent among study participants who quit smoking.

“That may not sound like much,” but research shows that translates to a 14 percent lower risk of developing heart disease, Stein said.

With the small improvement at one year, the question is, do ex-smokers keep getting better?

The study is continuing another two years to find an answer, Stein said.