Regular exercise is great for your heart. Period. But some recent studies have suggested that too much exercise might actually hinder heart health, prompting doctors to question the merits of grueling, months-long marathon training. An innovative new study should silence those skeptics. Researchers from the University of Hartford in Connecticut found that training for a marathon does not harm the heart and may indeed help it, although it doesn't necessarily erase damage caused by other factors, such as smoking in earlier years or eating an unhealthy diet. 

Here's why this study is so unique – and telling: In order to root out the cardiovascular effects of endurance training from other markers of heart health – a task that has flummoxed scientists in the past – the researchers examined 42 Boston Marathon entrants along with their non-running spouses. They did this on the assumption that, aside from the intense training, both partners likely had similar dietary and lifestyle habits. 

The day before the race, the researchers measured everybody's cholesterol levels, blood pressure, body weight, and other markers of inflammation, along with their arterial thickness – a cardiovascular risk factor that paints a good picture of heart health. "We did not find any evidence that runners had greater atherosclerotic progression, or thickening of the arterial wall, relative to their spouses," says lead study author Beth Taylor. "Since there was no difference between runners and their spouses, these results are reassuring that long-term, chronic, high-intensity exercise does not damage the heart."

And since the spouses of these marathoners also proved to be very healthy, Taylor believes they've reaped some of their partners' hard training. "Although the spouses weren't quite as healthy as the runners, we saw little evidence of cardiovascular disease risk," she says. "There was obviously some bias in our study because people who agree to be in studies on running and health are probably pretty motivated and healthy. However, we speculate that being married to a marathoner gives the spouse some extra lifestyle incentive and encouragement to stay healthy."

As for the runners themselves, the tests confirmed that training has likely improved their heart health, but it isn't a cure-all. Some of the marathoners had signs of stress or damage likely caused by other and past behaviors. So, in a nutshell, "strenuous running is neither panacea nor poison for perfect cardiovascular health," says Taylor.

Marathoners – and their lovers – may not be the only ones who reap such heart-health perks. "Some of the other endurance sports such as cross-country skiing have also been implicated as being potentially damaging to the heart," Taylor says. "But I think any exercisers who participate in high-intensity, sustained endurance training could find relevance in these results."