By Amy Norton

NEW YORK (Reuters Health) - Offering yet another reason to never start smoking, a new study finds that both current and former smokers run an elevated risk of the heart rhythm disorder atrial fibrillation.

The condition, also known as AF, is the most common heart arrhythmia in the U.S., affecting about 2 million people. During an episode of AF, abnormal electrical activity in the heart causes its upper two chambers to beat in a rapid, uncoordinated rhythm; the arrhythmia itself is not life-threatening, but over time AF can contribute to stroke or heart failure in some people.

While smoking is a well-known risk factor for heart disease, it has not been clear whether the habit boosts the risk of AF specifically.

The new findings, reported in the American Heart Journal, suggest that it does -- even after a smoker quits.

Researchers found that of nearly 5,700 Dutch adults age 55 and older, current smokers and former smokers were about 50 percent more likely to develop AF over 7 years.

The bottom line, lead researcher Dr. Jan Heeringa told Reuters Health, is that AF "has to be added to the long list of diseases" linked to smoking.

"An independent effect of smoking on atrial fibrillation has never been found, until now, in our study," noted Heeringa, of Erasmus Medical Center in Rotterdam, the Netherlands.

Even when the researchers took other factors into account -- such as age, and whether participants had high blood pressure or had ever suffered a heart attack -- smoking itself was still linked to higher AF risk.

It is surprising that former smokers had an AF risk comparable to current smokers', according to Heeringa.

But the finding does not mean that quitting the habit is "meaningless," the researcher stressed. It's known that smokers who quit lower their risk of developing a number of smoking-related ills, including lung cancer and heart attacks.

"Stopping of smoking, at any age, has huge beneficial effects on health," Heeringa said.

SOURCE: American Heart Journal, December 2008.

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