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Insomnia and stressful life events may explain why some women develop an irregular heart rhythm after menopause, new research finds.

Psychosocial factors are "the missing piece to the puzzle" that can lead to atrial fibrillation, or AFib, the study's lead author said. The findings were published Wednesday in the .

"I see many postmenopausal women with picture-perfect physical health who struggle with poor sleep and negative psychological emotional feelings or experience, which we now know may put them at risk for developing atrial fibrillation," lead author Dr. Susan X. Zhao said in a . Zhao is a cardiologist at Santa Clara Valley Medical Center in California.

Traditional AFib risk factors include older age, high blood pressure, diabetes and obesity. The irregular heart rhythm may lead to blood clots, stroke, heart failure and other cardiovascular problems. AFib primarily affects older adults, and more than 12 million people in the U.S. are expected to develop it by 2030, according to .

Previous studies have shown that because women live longer than men, they may face higher risk and worse outcomes related to AFib.

Researchers analyzed data of more than 83,000 women who participated in the , an ongoing health study in the United States. The women's ages ranged from 50 to 79, and the majority were white.

The participants answered questions about stressful life events, such as the loss of a loved one, illness, divorce, financial pressure, and domestic, verbal, physical or sexual abuse. Questions about their sleeping habits focused on overall quality and if they had trouble falling asleep or woke up during the night. Other questions addressed their life and social supports and their sense of optimism.

More than 1 in 4 participants developed AFib during an average follow-up period of about a decade. For each additional point on the insomnia scale, there was a 4% higher likelihood of developing AFib. Each additional point on the stressful life event scale resulted in a 2% higher likelihood of the heart condition.

"The heart and brain connection has been long established in many conditions," Zhao said. AFib "is prone to hormonal changes stemming from stress and poor sleep. These common pathways likely underpin the association between stress and insomnia with atrial fibrillation." Stressful life events, however, though significant and traumatic, may not last long, she said.

The reliance on patient questionnaires at the start of the study limited the research, the authors said. They called for more research to confirm the links between psychosocial stress, emotional well-being and the development of AFib.