Obesity raises the risk of atrial fibrillation, an abnormal heartbeat that can lead to stroke and early death if not controlled, researchers said on Tuesday.

"What we found is that obesity was associated with an approximately 50 percent increase in the risk of developing atrial fibrillation," said Dr. Thomas Wang of the Framingham Heart Study.

The researchers tracked more than 5,200 middle-aged adults for an average of 14 years, during which 526 developed atrial fibrillation, mostly due to changes in the structure of the heart blamed on patients being overweight.

Obesity can cause the heart's left atrium, an upper chamber that receives oxygenated blood circulated from the lungs, to become dilated and beat abnormally fast, throwing off the heart's rhythm, according to the study published in the Journal of the American Medical Association.

"Once you get atrial fibrillation, it may be very difficult for doctors to get you back into the normal rhythm, and what that means for the patient is that the patient may be stuck with a lifetime of taking medications to protect against stroke and the other complications of atrial fibrillation," Wang said.

Beta-blockers are often used to treat the irregular heartbeat and can have side effects, such as aggravating lung disease symptoms or reducing circulation to the limbs.

Uncontrolled atrial fibrillation, which is reaching epidemic proportions as the U.S. population ages, raises the risk of stroke up to five-fold and doubles the risk of death, according to an accompanying editorial by Dr. James Coromilas of Columbia University Medical Center in New York.