TUESDAY, Jan. 17 (HealthDay News) -- Middle-aged men with blood pressure in the upper-normal range are at increased risk for atrial fibrillation later in life, researchers say.

Atrial fibrillation -- which affects more than 2.7 million Americans -- is a heart rhythm disorder that can lead to stroke and other heart-related complications. High blood pressure is a known risk factor for atrial fibrillation.

Previous research has shown that women with blood pressure in the upper end of the normal range are at increased risk for atrial fibrillation. This study looked at whether the same was true in men.

In the new study, Norwegian researchers analyzed data from more than 2,000 men aged 40 to 59 who had their blood pressure measured at the start of the study and were followed for up to 35 years. During the follow-up, 270 (13 percent of the men) developed atrial fibrillation.

U.S. guidelines define high blood pressure as systolic pressure (top number) at 140 millimeters of mercury (mm Hg) or higher and diastolic pressure (bottom number) at 90 mm Hg or higher. Pre-hypertension is a systolic pressure of 120 to 139 mm Hg and a diastolic pressure from 80 to 89 mm Hg.

Men with high systolic blood pressure at the start of the study were 60 percent more likely to develop atrial fibrillation during follow-up than those with normal systolic blood pressure.

Men with upper-normal levels of systolic blood pressure (128 to 138 mm Hg) were 50 percent more likely to develop atrial fibrillation than those with normal systolic blood pressure (below 128 mm Hg), the investigators reported.

And, they found, men with a diastolic of 80 mm Hg or higher at the start of the study were 79 percent more likely to develop atrial fibrillation than those with diastolic blood pressure below 80 mm Hg (normal).

On average, according to the report published in the Jan. 17 edition of the journal Hypertension, atrial fibrillation developed 20 years after the start of the study.

"Our results indicate that men with upper-normal blood pressure appear to have a higher risk for [atrial fibrillation] than men with lower blood pressure," lead author Dr. Irene Grundvold, a consultant cardiologist in the cardiology department at Oslo University Hospital, said in journal news release.

More information

The U.S. National Heart, Lung, and Blood Institute has more about atrial fibrillation.