It takes only days for your body to start thanking you for butting out for good, according to new study findings reported on Monday.

Japanese investigators found that 14 days after a group of smokers quit, their blood became significantly less likely to form clots, putting them at a lower risk of heart attack or stroke.

However, Dr. Stavros Konstantinides of the University of Goettingen in Germany, who was not involved in the study, cautioned that the findings do not suggest that it takes only days for smokers’ bodies to become as healthy as non-smokers’.

These findings provide “extra motivation for people to quit smoking,” he told Reuters Health, but they need to stick with it for more than two weeks to get the full health benefits.

During the study, Hirohiko Morita of the Kurume University School of Medicine and colleagues asked 27 men who had smoked at least 15 cigarettes per day for more than 5 years to quit. Half of the men were allowed to start smoking again after 2 weeks, while the other half remained abstinent for 4 weeks.

The researchers followed smokers over time, noting how their blood responded when they quit.

Reporting in the Journal of the American College of Cardiology, the researchers found that within 2 weeks, former smokers’ blood underwent changes that rendered it less likely to clot, an established risk of smoking. Once people began smoking again, their apparent risk of blood clots climbed to its pre-quitting level.

“This was really an effect that can come really fast after stopping smoking,” Konstantinides noted.

He added that the study did not examine the actual risk of blood clots, stroke or heart attack, just factors that tend to influence clotting.

In an interview, Konstantinides explained that blood function takes only days to respond to a non-smoking environment because smoking has a very immediate effect on the blood. However, smoking damages blood vessels much more slowly, he said, so, in turn, it takes much longer for blood vessels to recover from smoking.

He added that the study participants were all very healthy, and quitting smoking may have different effects on blood function in men who already have medical problems such as heart disease, for example.

SOURCE: Journal of the American College of Cardiology, February 15, 2005.