Teenagers who are overweight, even mildly so, may face a higher risk of developing a disease of the heart muscle later in life.

The study focused on cardiomyopathy, a disease of the heart muscle that can affect the size and shape of the heart, as well as the thickness of the muscle wall. The condition can reduce heart function and lead to heart failure, which means the heart is not able to pump blood properly around the body.

Swedish researchers analysed data on over 1.6 million young men who had enlisted in compulsory military service in Sweden between 1969 and 2005. The participants were all aged 18 and 19 when they enlisted and they were followed up for up to 46 years.

The study found that the men who had been most lean at the age of 18 had the lowest risk of developing cardiomyopathy later in life. However, as weight increased, so did the risk of the heart condition. Even men who were at the high end of a normal body mass index (BMI) displayed some increased risk.

A normal BMI is 18.5 to 24.9, while 25 and over is classed as overweight. Thirty and above is classed as obese.

The researchers found that those who had a BMI of 35 or above as teenagers were eight times more likely to develop dilated cardiomyopathy later in life. This is a form of the condition in which the heart muscle becomes weak and so cannot pump blood efficiently.

"We were interested in studying cardiomyopathies, because heart failure caused by this historically uncommon disorder doubled in Sweden between 1987 and 2006," explained Dr Annika Rosengren of the University of Gothenburg and Sahlgrenska University Hospital.

However while this study was carried out on Swedish men, the researchers believe that due to its large size, the results probably apply to men worldwide. However, it is unclear whether they also relate to women.

Details of these findings are published in the journal, Circulation.