Danger of too much exercise after heart attacks, New Study

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.

Cardiovascular exercise like running or walking has a number of health benefits. But too much exercise may be unhealthy, especially after a heart attack.

A recent study found benefits associated with exercise up to a point. Those running or walking the most, however, had an increased risk of death from heart attacks or other heart problems.

The study was written by Paul Williams, PhD, of Lawrence Berkeley National Laboratory in Berkeley, CA, and Paul Thompson, MD, of Hartford Hospital in Hartford, CT.

The research examined whether more exercise decreased the risk of death in patients who survived a heart attack. A heart attack occurs when blood flow to the heart is stopped, usually by a blood clot.

The authors used two large-scale studies where people self-reported whether they had had a heart attack and how much and how often they walked or ran for exercise.

Patients were divided into groups based on the authors’ calculation of how much energy they expended. They measured expended energy in metabolic equivalent of task-hours per day, or MET-h/d.

A measure of 1 MET-h/d is the same as running 0.62 miles each day.

Of the 2,402 study participants, 526 died during an average follow-up period of 10.4 years. Of those deaths, 376 were related to heart disease.

The researchers found that the risk of death related to heart disease decreased as the amount of energy used running or walking increased.

Meeting recommended exercise levels between 1.07 and 1.8 MET-h/d decreased the risk of heart-related death by 21 percent, compared to less exercise.

Between 1.8 and 3.6 MET-h/d reduced the risk of heart-related death by 24 percent.

Patients exercising between 3.6 and 5.4 MET-h/d had a 35 percent lower risk of heart-related death than those exercising less than the suggested amount.

For participants burning 5.4 to 7.2 MET-h/d, there wasn’t a difference in risk reduction compared to the group expending 3.6 to 5.4 MET-h/d. The authors wrote that this finding represented a “plateau of risk reduction.”

Comparing participants expending 3.6 MET-h/d with those reporting 7.2 MET-h/d, the authors found that, at the higher level of exercise, heart-related death was 2.62 times more likely.

“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,” Drs. Williams and Thompson said in a press release. “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.”

The authors acknowledged that they studied heart attack survivors, who might have different risks than other groups.

Agencies/Canadajournal