A striking new global study has found that two seemingly unrelated conditions—breast cancer and atrial fibrillation, a common irregular heartbeat known as AFib—are following remarkably similar patterns across much of the world. The findings suggest that millions of women could lower their risk of both diseases by tackling the same lifestyle habits, particularly smoking and alcohol consumption.

The research, published on recently in the Journal of the American Heart Association, analysed health data from women aged 55 years and older across 204 countries and territories using the Global Burden of Disease 2021 database. Researchers also employed machine learning—computer systems trained to identify hidden patterns in vast amounts of data—to map where the two diseases occur together and uncover the risk factors they share.

The results surprised even the investigators. Around 40% of the countries studied showed similar rates of both breast cancer and atrial fibrillation/flutter, an irregular heartbeat that can increase the risk of stroke, heart failure and other serious complications. High-income countries including the United States, Canada, Australia, New Zealand and many European nations consistently emerged as high-risk regions.

"Identifying shared risk factors is important for developing interventions that support optimal health, such as smoking cessation and alcohol restriction, which could potentially reduce the global incidence of breast cancer and atrial fibrillation/flutter substantially," said Dr Shu Wang, director of the Breast Disease Center at Peking University People's Hospital in Beijing and a co-author of the study.

After examining exposure to 58 behavioural, environmental and metabolic risk factors, the researchers identified smoking and alcohol use as the strongest common contributors. Their analysis estimated that reducing alcohol intake and smoking worldwide could potentially lower breast cancer cases by about 15% and atrial fibrillation/flutter by around 12%.

Alcohol alone was estimated to account for 9.27% of breast cancer cases and 7.57% of atrial fibrillation/flutter cases globally.

The geographical overlap also points to broader lifestyle changes accompanying economic development. Western countries generally reported higher exposure to smoking, alcohol consumption, obesity, physical inactivity and calorie-rich diets—risk factors that previous research has consistently linked with both cardiovascular disease and several cancers. Earlier scientific statements from the American Heart Association have likewise highlighted that maintaining a healthy weight, exercising regularly, avoiding tobacco and limiting alcohol can reduce the risk of both heart disease and breast cancer.

"One of the most surprising aspects of our findings was how common both breast cancer and atrial fibrillation/flutter diagnoses were among women ages 55 and older in high-income regions, which highlights the influence of lifestyle," Dr Wang said. "This is the first study combining global data with machine learning to show the relationship between the conditions, their location across the world and the shared risk factors."

Dr Zeye Liu and Dr Yi Shi, cardiac surgeons and study co-authors from Peking University People's Hospital, said growing evidence is bringing cancer and cardiovascular health closer together than previously recognised.

"Breast cancer and atrial fibrillation/flutter rise together across many regions of the world and share the same modifiable risk factors. From a cardiovascular perspective, this means that reducing smoking and alcohol use could help lower the risk of both conditions at the same time," they said.

Commenting independently, Dr Laxmi Mehta, Chair of the American Heart Association's Council on Clinical Cardiology, said the findings reinforce what preventive medicine has been suggesting for years.

"Many of the same modifiable factors—including smoking, alcohol use, poor diet, physical inactivity and obesity—contribute to both breast cancer and cardiovascular disease, including atrial fibrillation/flutter," she said, adding that integrated lifestyle strategies could help prevent both illnesses.

The researchers cautioned that the study identifies associations rather than proving that one disease causes the other. Because the analysis relied on country-level data, differences in healthcare systems, screening programmes and data quality may also have influenced the results. Even so, the newly developed global risk maps could help governments design more targeted prevention programmes while guiding future research incorporating genetic, metabolic and socioeconomic information.

For ordinary women, the message is refreshingly simple. Diseases affecting different organs may still share the same roots. Avoiding tobacco, drinking less alcohol, staying physically active, maintaining a healthy weight and eating a balanced diet may not only protect the heart but also reduce the risk of one of the world's most common cancers—offering a powerful reminder that healthier everyday choices can deliver benefits across the whole body.