More exercise may not always be better, according to a recent study.

Researchers found that while regular physical activity, such as brisk walking and jogging, keeps the heart healthy and lower the risk of death from other diseases such as hypertension, and stroke, too much exercise can contribute to cardiovascular deaths.

The Physical Activity Guidelines for Americans recommends about 150 minutes per week of moderate-intensity exercise or about 75 minutes of vigorous-intensity exercise.

"These analyzes provide what is to our knowledge the first data in humans demonstrating a statistically significant increase in cardiovascular risk with the highest levels of exercise," researchers wrote in the study. "Results suggest that the benefits of running or walking do not accrue indefinitely and that above some level, perhaps 30 miles per week of running, there is a significant increase in risk. Competitive running events also appear to increase the risk of an acute event."

For the study, researchers examined the relationship between exercise and cardiovascular disease-related deaths in nearly 2,400 physically active heart attack survivors. They conducted a prospective long-term study using National Walkers' and Runners' Health Studies databases.

They discovered that remarkable dose-dependent reductions in deaths from cardiovascular events of up to 65 percent were seen among patients who were running less than 30 miles or walking less than 46 miles per week. Beyond this point however much of the benefit of exercise was lost, in what is described as a reverse J-curve pattern.

"Extrapolation of the data from the current Williams and Thompson study to the general population would suggest that approximately one out of twenty people is overdoing exercise," James H. O'Keefe from the Mid America Heart Institute and first author of an editorial on "Exercising for Health and Longevity versus Peak Performance: Different Regimens for Different Goals," which appears in the same issue. Along with co-authors Carl "Chip," said. "We have suggested the term 'cardiac overuse injury' for this increasingly common consequence of the 'more exercise is better' strategy."

Even so, the researchers said that about 10 out of every twenty people are not getting the minimum recommended amount of physical activity.

The findings were recently published in the journal Mayo Clinic Proceedings.