A new study published in Mayo Clinic Proceedings finds that heart attack survivors who exercise excessively are at increased risk of dying from heart problems. However, regular physical activity is recommended for managing heart disease and lowering the risk of death from high blood pressure, stroke and type 2 diabetes.

In the new study, researchers from the Department of Cardiology, Hartford Hospital, Hartford, CT, analyzed data from the National Walkers’ and Runners’ Health Studies databases, involving about 2,400 physically active heart attack survivors.

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According to the Physical Activity Guidelines for Americans, we need about 150 minutes per week of moderate-intensity exercise or 75 minutes per week of vigorous-intensity exercise.

The results confirm previous findings that the benefits to the heart of walking and running are about the same, as long as the energy expended is the same. However, when walking rather than running, it takes about twice as long to burn an equal number of calories.

The study also found that deaths from heart problems decreased up to 65% among patients who ran less than 30 miles per week or walked less than 46 miles per week. Exercising more than this, however, resulted in the benefits of exercise being lost.

The authors explain:

“These analyses 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.”

“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,” they add.

However, the authors admit that because all of the patients in their study were heart attack patients, it may not be possible to generalize their findings to all heavy exercisers.

An editorial on the subject by Dr. James O’Keefe, from the Mid America Heart Institute in Kansas City, MO, says that on the basis of the Hartford study, about 1 out of every 20 people is overdoing exercise. “We have suggested the term ‘cardiac overuse injury’ for this increasingly common consequence of the ‘more exercise is better’ strategy,” he says.

Despite this, O’Keefe also points out that the study finds that about 10 in every 20 people are not getting the minimum recommended amount of exercise.

According to the Physical Activity Guidelines for Americans, we need about 150 minutes per week of moderate-intensity exercise or 75 minutes per week of vigorous-intensity exercise.

He explains that several studies have found about 5 hours of vigorous exercise per week to be the safe upper range for long-term heart health and life expectancy. Also, people should not engage in high-intensity exercise every day and should abstain from exercising 1-2 days a week.

O’Keefe’s co-author Dr. Carl “Chip” Lavie, cardiologist at the John Ochsner Heart and Vascular Institute, New Orleans, LA, adds:

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.

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.’ I and my co-authors believe this assessment continues to provide wise guidance.”

As well as the editorial and Hartford study, the same issue of Mayo Clinic Proceedings also includes a meta-analysis of 10 cohort studies assessing 42,000 athletes participating in a wide range of sports.

The meta-analysis found that athletes live longer than the general population, “which suggests that the beneficial health effects of exercise, particularly in decreasing cardiovascular disease and cancer risk, are not necessarily confined to moderate doses,” comments senior investigator Dr. Alejandro Lucia of the European University Madrid, Spain. “More research is needed however, using more homogeneous cohorts and a more proportional representation of both sexes.”