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A study led by researchers from the Medical Research Council Population Health Research Unit at the University of Oxford (MRC PHRU), and the Nuffield Department of Population Health, has found that measuring body mass and waist circumference could help identify those most at risk of a severe disease. The results are published today in the Journal of the American Heart Association.

Millions of people across the world are affected by atrial fibrillation (AF), a condition where the heart beats irregularly and does not contract as it should, which can cause blood clots. This doubles the risk of heart-related death and is associated with a five-fold increase in stroke risk. Many of these could be avoided using preventative therapies such as anticoagulation treatments that reduce blood clotting. AF can be asymptomatic, however, and thousands are unaware that they have the condition. In the UK alone, there are thought to be 300,000 people living with undiagnosed AF, with the total affected being over 1.6 million.

Identifying those at risk of AF is therefore a clear health priority. Previous research has established a strong link between obesity and AF. Those who are obese are more likely to develop AF, and also more likely to die of a cardiac condition or stroke compared to those with AF who have a healthy weight. Until now, however, it has been unclear what measures of obesity can best predict AF risk, and whether these are different for men and women.

The researchers investigated this by analysing body mass index or BMI (a measure of body mass relative to a person’s size calculated by dividing their weight in kilograms by the square of their height in metres), waist circumference and electrocardiogram data gathered between 2008 and 2013 from over 2 million adults in the USA and United Kingdom. The study included 12,000 adults with AF, and is one of the largest studies to date to assess the association between AF and obesity. After adjusting for factors such as high blood pressure, diabetes and smoking, the data showed that both higher BMI and a larger waist circumference were associated with an increased risk of AF in men and women.

In men, there was a stronger association between waist circumference and AF risk, whilst in women BMI was the stronger indicator of AF. Waist circumference improved the ability to predict AF in men by 30%, compared with 23% using BMI. In women, BMI improved the ability to predict AF by 23% compared with 12% for waist circumference.

Since both BMI and waist circumference are simple to measure, this knowledge could help clinicians across the world to identify those most at risk of AF.

Dr Richard Bulbulia, co-senior author of the study and a research fellow in MRC PHRU said: ‘As obesity rates increase across the world, our findings make public health interventions to avoid weight gain increasingly pressing. They also point to an exciting next question to research: can weight loss decrease the severity of AF in those who have it, or prevent people from developing it? What we need now are intervention studies to demonstrate whether intentional weight loss can reduce the risk of AF.’