Even the slow joggers were getting vigorous exercise, the researchers said. But in a report published Monday in the Journal of the American College of Cardiology researchers from Denmark say that people who push their bodies too hard may essentially undo the benefit of exercise. In Lee's own study of 55,000 adults, including more than 13,000 runners, he found a lower risk of death over the follow-up period in joggers with the highest running time and frequency—nearly three hours a week and at least six times a week—compared with non-runners. Even people who ran slightly more, for 2.5 hours to four hours a week at an average pace less than three times a week, showed slightly higher mortality risk, at 66%, something that came as a surprise to the authors. Cohen—Courtesy of Boston Children's Hospital Getty Images 1 of 10 Advertisement 
 
 “I would expect the light joggers to have really low risk,” says Jacob Marott, a researcher at the Copenhagen City Heart Study at Frederiksberg Hospital and one of the study’s co-authors. “But regarding the moderate joggers, I was a little surprised they didn’t have a bigger benefit from jogging than the light joggers. The study's good news, Lee said, is that the researchers found benefit even in jogging less than an hour a week, or even once a week, compared to not jogging at all.
– It's common knowledge that a healthy person shouldn't sit around all day, but new research on running is emphasizing the opposite danger. Running too much can be just as bad for you as being sedentary, the study suggests. Researchers tracked some 1,100 healthy runners and 413 sedentary folks over a period of more than 12 years, HealthDay reports via Medical Xpress. People ranged in age from 20 to 95. The risk of dying during the study turned out to be approximately the same among heavy runners—those who ran quickly more than three days a week for a total of more than four hours—and sedentary people who rarely exercised, Time reports. The best plan, according to the study, was to run lightly: The group that had the best results ran at a slow-ish pace (about 5mph) less than three times each week, going for an hour to 2.4 hours total. Even a group that ran a bit more often and longer saw a slight increase in death risk, Time notes. The findings could perhaps relate to cardiovascular problems previously observed in the most die-hard runners and cyclists. "If you want to do something good for yourself, you don’t have to be extreme," says a study author. But another researcher points to a number of possible flaws in the findings, including the fact that the hardest-running group was quite small. (Another recent study has a warning on exercise: It could hurt your teeth.)