A light jog a few times a week may help you live longer but running too hard may actually be harmful, a new study has found.

Researchers in Denmark analysed information from about 1,000 healthy joggers ages 20 to 86, and around 400 people who were healthy, but did not jog, and were mostly sedentary.

They found that light joggers were about 78 per cent less likely to die over the 12-year study than those who were sedentary.

Light joggers were defined as those who ran at a speed of about 8 km/h a few times a week, for less than 2.5 hours per week total.

In contrast, those who jogged strenuously were just as likely to die during the study period as those who were sedentary, according to the research published in the Journal of the American College of Cardiology.

Strenuous joggers were defined as those who ran at a speed of more than 11 km/h, for more than four hours per week, ‘Live Science’ reported.

The finding "suggests there may be an upper limit for exercise dosing that is optimal for health benefits," study co-author Dr Peter Schnohr, of the Copenhagen City Heart Study and Frederiksberg Hospital in Denmark, said.

"If your goal is to decrease risk of death and improve life expectancy, jogging a few times a week at a moderate pace is a good strategy. Anything more is not just unnecessary, it may be harmful," Schnohr said.

The study adds to a growing body of evidence that has shown that even small amounts of exercise can have health benefits.

In the study, people who jogged less than one hour a week were less likely to die than those who didn’t jog at all.

The best outcomes in the study were associated with running between 1 and 2.4 hours per week, with no more than three days of running per week, at an average or slow pace.

"The goal is not to unnecessarily frighten people who wish to participate in more-strenuous exercise," Duck-chul Lee, of Iowa State University’s Department of Kinesiology, and colleagues, wrote in an editorial accompanying the study in the journal.

Although most research suggests that, beyond a certain point, more physical activity is not necessarily better, "we still need more data to truly determine ‘is more actually worse?’" they said.

The authors of the editorial also noted that in the new study, the "strenuous" jogging group included only 40 people, while the other groups included hundreds.