Teenagers who are physically fit are less likely to suffer a heart attack later in life, the results of a new study indicate.

Swedish scientists looked at over 740,000 men who had undergone medical examinations between 1969 and 1984, when they were 18 years of age. Their aerobic fitness was tested at the age of 18 using a cycling test - resistance was gradually increased until they were too exhausted to cycle any more.

The men were monitored for an average of 34 years.

The study found that the more aerobically fit the men were at the age of 18, the less likely they were to suffer a heart attack 30 or 40 years later. In fact, every 15% increase in aerobic fitness was associated with an 18% reduced risk of suffering a heart attack 30 years later.

The scientists also found that 18-year-olds who regularly undertook cardiovascular training, such as running, cycling and swimming, reduced their risk of a heart attack later in life by 35%.

The study noted that the association between aerobic fitness and heart attack risk was present regardless of the participants' body mass index (BMI) when they were teenagers. However, it also noted that men who were fit, but overweight or obese, had a much higher risk of suffering a heart attack compared to thinner men who were unfit.

In fact, the fittest obese men were almost twice as likely to suffer a heart attack compared to the most unfit thinner men. They were also four times more likely to suffer a heart attack compared to the fittest thinner men.

"Our findings suggest that high aerobic fitness in late adolescence may reduce the risk of heart attack later in life...Given the strong association that we have found, the low cost and easy accessibility of cardiovascular training, and the role of heart disease as a major cause of illness and death worldwide, these results are important with respect to public health," said lead scientist, Prof Peter Nordström, of Umeå University.

Details of these findings are published in the European Heart Journal.