We all know that running a few kilometers each day is good for our health, right? And a little time spent on training is useless. Well, what we didn't know, until now, is that running too much could be bad for us. New research suggests that running long distances regularly for many years could shorten our life instead of extending it. The study is from the Minneapolis Heart Institute Foundation. Researcher Dr James O'Keefe said too much running can cause plaque . This can lead to heart disease. He wrote: "Years of extreme exercise…appears to erase some benefits you get from moderate exercise, so that your risk of heart disease, of dying of coronary disease, is the same as an inactive person."

The researchers looked at the health and training of 3,300 runners over the age of 35. Seventy per cent of them ran more than 30 kilometres a week. Such people can hardly be called unhealthy. But the study found that men who were marathon runners for 25 years had 62 per cent more plaque in their heart than men of the same age who did a little training or no exercise. Another doctor and long-time runner, John Hagan, said he felt cheated . He has been running marathons and doing triathlons since 1967. He used to run up to 60 kilometres per week. He said: "As a physician and a runner, I felt so  betrayed . I thought I was out there exhausting myself, building an absolutely indestructible heart. It was really hard work to do." Dr Hagan advised people to exercise regularly but not to overdo things.