Moderate caffeine consumption does not appear to trigger an abnormal rhythm of the atria, the upper chambers of the heart, new research reports.

Danish investigators evaluated the effects of caffeine, consumed through coffee, tea, cola, cocoa or chocolate, in almost 48,000 people. The investigators found that those who consumed the most caffeine per day - roughly 1,000 milligrams, or about 10 cups of coffee - were no more likely to experience Atrial Fibrillation or flutter than people who drank the least amount, equivalent to between 2 and 3 cups of coffee each day.

In an accompanying editorial, Drs. Martijn B. Katan and Evert Schouten of Wageningen University and Research Center in the Netherlands, note that caffeine also does not appear to cause abnormal rhythms in the lower chambers of the heart, called ventricles, which can be deadly.

Although atrial fibrillation and flutter are less dangerous than ventricle rhythm abnormalities, they can still cause palpitations, problems in blood circulation, and fainting. Atrial fibrillation affects up to 10 percent of people over age 65.

The editorialists add that even if caffeine doesn’t disturb heart rhythm, it appears to raise blood pressure slightly, and increase the body’s concentration of homocysteine, high levels of which have been linked to heart disease.

“That effect is enough to justify counseling high-risk patients to moderate their caffeine intake, but other interventions - e.g., smoking cessation, weight loss, exercise, and a healthy diet low in saturated and trans fats - yield larger benefits and should come first,” they write.

During the study, Drs. Lars Frost and Peter Vestergaard of Aarhus University Hospital and his colleague followed 47,949 people for an average of nearly 6 years, noting what they ate and drank and who developed atrial fibrillation or flutter.

Reporting in the American Journal of Clinical Nutrition, the authors found that people who drank more than the equivalent amount of caffeine in 2 to 3 cups of coffee were no more likely to develop atrial fibrillation or flutter during the study.

In the editorial, Katan and Schouten note that the same study found that people who drink relatively large amounts of alcohol are more likely to develop atrial fibrillation.

“This consistent finding increases confidence that an effect of coffee on atrial fibrillation would have been detected if it existed, because people tend to report their coffee intake more accurately than their intake of alcohol,” they write.

SOURCE: American Journal of Clinical Nutrition, March 2005.