Unfit lean men are less likely to have heart attacks than obese fit men, a new study has shown.

Researchers at a Swedish university also found that men were less likely to have heart attacks if they were continuously physically active as teenagers.

In fact, men who exercise late into their teenage years lessen the risk of a premature heart attack by 35 percent.

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When variables including a man’s BMI and his socio-economic background are taken into account, each time his fitness rises by 15 percent, his chance of having a heart attack in 30 years’ time reduces by 18 percent.

The findings published in the European Heart Journal come from the analysis of 743,498 Swedish men who were medically examined when they were conscripted into the army aged 18, between 1969 and 1984.

Scientists at Umeå University then continued to monitor the men’s records until January 2011, or when the subject suffered a heart attack, depending on which happened first.

Peter Nordström, one of the researchers, said: "as cardiovascular disease is such as a big public health problem and fitness training is both readily-available and affordable, these results and these types of study are important for the planning of preventative public health programmes.”

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He also explained that having a normal weight is more important than being in a good physical shape, adding: “it is even better to be both fit and have a normal weight”.

“While being physically fit at the end of your teens can reduce the risk of heart attack, fitness alone does not appear to fully compensate for the risks with being overweight or obese,” he said.

However, Nordström continued: “the study only shows that there is a correlation between fitness and a reduced prevalence of heart attack; we were unable to show specifically that a higher level of physical fitness reduces the risk of heart attacks.”

He also stressed that the connection between fitness and heart disease is highly complicated and can be influenced by a number of factors, including genetic predisposition.