Too much exercise may be bad for heart: study

Exercise is good for your health, but a new study out Tuesday found "clear evidence" of an increase in cardiovascular deaths in heart attack survivors who exercise too much.

The study, published in the U.S. journal Mayo Clinic Proceedings, analyzed the relationship between exercise and cardiovascular disease-related deaths in about 2,400 physically active heart attack survivors.

Remarkable reductions in deaths from cardiovascular events were seen among patients who were running less than 30 miles (about 48 kilometers) or walking less than 46 miles (about 74 kilometers) per week.

Beyond this point, however, much of the benefit of exercise was lost, in what is described as a reverse J-curve pattern.

"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," said the study led by Paul Williams of the Lawrence Berkeley National Laboratory and Paul Thompson of the Hartford Hospital.

"Competitive running events also appear to increase the risk of an acute event."

However, the researchers pointed out that as the study was based on heart attack survivors, the findings cannot be readily generalized to the entire population of heavy exercisers.

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

"For patients with heart disease, almost all should be exercising, and generally most should be exercising 30-40 minutes most days, but from a health stand-point, there is no reason to exercise much longer than that and especially not more than 60 minutes on most days," said Carl Lavie, a cardiologist at the John Ochsner Heart and Vascular Institute in New Orleans.

"As Hippocrates said more than 2,000 years ago, 'if we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health,'" he concluded.