Just an hour or two a week confers life-extension benefits, researcher contends. (HealthDay)—A little jogging is good for your health, researchers say, but too much might not be. 
 
 "In this study, the dose of running that was most favorable for reducing mortality was jogging 1 to 2.4 hours per week, with no more than three running days per week," said study researcher Jacob Marott of the Frederiksberg Hospital in Copenhagen, Denmark. The best pace was slow or average—about 5 miles per hour, he added. 
 
 Out of a pool of about 5,000 healthy Danish adults, Marott and his colleagues followed nearly 1,100 healthy joggers and 413 sedentary people for more than 12 years. The joggers noted their hours and frequency of jogging, and their perception of their pace. 
 
 The strenuous joggers, the investigators found, were as likely to die during that time period as the sedentary non-joggers. Light joggers and moderate joggers fared better, in that order, Marott's team found. 
 
 The findings were released online Feb. 2 in advance of publication in the Feb. 10 print edition of the Journal of the American College of Cardiology. 
 
 What is it about strenuous running that might be harmful? "We believe that long-term strenuous endurance exercise may induce pathological structural remodeling of the heart and large arteries," Marott said. 
 
 However, a U.S.-based researcher said the debate about the optimal dose of running for longevity is far from resolved. 
 
 The new study has limitations, said D.C. (Duck-chul) Lee, an assistant professor of kinesiology at Iowa State University, who co-authored an editorial accompanying the study. 
 
 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. It was published in 2014, also in the Journal of the American College of Cardiology. 
 
 In the Copenhagen study, joggers self-reported their pace. Even the slow joggers were getting vigorous exercise, the researchers said. 
 
 "The reported pace was not an absolute pace in miles per hours, but the subjects' own perception of pace as slow, average or fast," Marott said. He said that's more appropriate than an absolute scale when the age range is as wide as it was in their study (ages 20 to 95). In general, however, the slow or average pace was about 5 miles per hour or a 12-minute mile, and the fast pace was 7 miles per hour or about an 8-minute mile, he said. 
 
 In the United States, about 54 million people run regularly, according to background information with the study. In 2013, more than 540,000 people finished a marathon (26.2 miles), and nearly 2 million completed a half marathon. 
 
 One limitation of the current study, Lee said, is that a very small group logged the most jogging time. Just 47 joggers put in more than four hours a week, and only 80 ran more than three times a week. These small numbers could have affected the comparisons and results, Lee said. 
 
 Also, the researchers didn't look at more than 3,500 active non-joggers who exercised in other ways, Lee said. The researchers looked only at death from all causes, he said, instead of looking to see if high jogging miles and times affected certain causes of death, which could have given more specific information about potential harms. 
 
 "More [running] may be worse only in cardiovascular disease," he said. In another assessments on the effects of running and death rates, Lee's group found that death from all causes was lower in runners compared with non-runners, regardless of how much they ran, but there was a slight trend for less benefit from higher doses when compared with lower doses. 
 
 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. Perhaps this will motivate sedentary people to get moving, he said. 
 
 Although the study by Marott and colleagues found an association between light jogging and improved survival rates, it did not prove a cause-and-effect relationship. 
 
 "Basically, the study still shows it's a much better option to prescribe some form of running as a part of a healthy lifestyle and that sedentary behavior is not a prescription for long-term health and mortality," said Dave Watt, executive director of the American Running Association and the American Medical Athletic Association. 
 
 Explore further: Regular jogging shows dramatic increase in life expectancy 
 
 More information: For tips on starting to exercise, see the American Heart Association. 
 
 ||||| Americans as a whole don’t exercise enough—at least that’s what the latest studies show—and so the message is clear: get more active, take walks, Let’s Move! Basically anything is better than sitting on the couch. But how much exercise is enough? That’s a hotly debated question for which experts still don’t have a satisfactory answer. But given that most of us are starting from a sedentary position, the assumption has long been the more the better. 
 
 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. Those who ran at a fast pace more than four hours a week for more than three days a week had about the same risk of dying during the study’s 12-year follow up as those who were sedentary and hardly exercised at all. The link held even after the researchers accounted for potentially confounding factors such as age, sex, whether the participants had a history of heart disease or diabetes, or whether they smoked and drank alcohol. 
 
 MORE This Is How Much Exercise Experts Really Think You Need 
 
 In fact, those with the lowest risk of dying during the study period were people who ran less than three times a week for one to 2.4 hours, at a slow to moderate pace. 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. 
 
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 “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. It made me think that if it’s really true, then exercise recommendations should take that into account.” 
 
 MORE It Doesn’t Matter How Much You Exercise If You Also Do This 
 
 What Marott and his team found was that both too little running and too much running are linked to higher rates of death. The most intense runners ended up with a risk of dying that was similar to that of those who opted to stay on the couch. Somewhere in between is the Goldilocks amount that’s just right to maintain heart health, burn off excess calories and keep blood sugar levels under control. And according to his results, that sweet spot is closer to the ‘less’ side of the curve than the ‘more’ side. 
 
 That dovetails with the mounting research that so-called micro-workouts—high intensity but brief workouts that could be as short at 1 minute, according to another recent paper—may be better for the body than long and continuous workouts. 
 
 That still means that some exercise is better than no exercise, but scientists may be getting more sophisticated about understanding that more isn’t always better, and that there may be a tipping point at which the harms of running start to outweighed its benefits. 
 
 Those negative effects might include things like changes in the structure and function of the heart and its vessels; previous studies showed that marathoners and long distance cyclists, for example, tend to be at higher risk of developing abnormal heart rhythms, and may be more vulnerable to enlarged hearts, which are less efficient at pumping blood and delivering oxygen and removing waste than normal-sized organs. 
 
 MORE Short Bursts of Exercise Are Better Than Exercising Nonstop 
 
 Marott acknowledges that it’s also possible that some other behaviors or factors common to avid runners, such as their exposure to the sun, which can increase their risk of skin cancer, might be explaining their higher risk of dying during the study. Other studies will have to investigate whether that’s the case, but in the meantime, Marott says “if you want to do something good for yourself, you don’t have to be extreme. Jogging one to four hours a week for no more than three days a week at a slow to moderate pace is actually achievable. And that’s a positive take-home message.” 
 
 Read next: 7 Reasons Why You’re Working Out and Still Not Losing Weight 
 
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– 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.)