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Exercise tied to heart risks for some. But don't cancel the gym membership

By Robert Bazell, Chief science and medical correspondent
NBC News

About 1 in 10 people may actually experience higher blood pressure, cholesterol levels and other risk factors for heart disease after exercising, concludes a survey of six studies that included a total of 1,697 volunteers published Thursday in the journal PLoS One.

The analysis from Pennington Biomedical Research Center, Louisiana State University, and several other research centers reported that the scientists don’t know why a group would have adverse heart effects from exercise. It was not related to age or fitness of the participants at the start of the study.

Many experts say the 10 percent figure is hardly surprising. To put it in perspective, if a new drug were to be effective in 90 percent of the people studied, it would be called hugely successful. 

“With any therapeutic intervention, there are always responders and non-responders,” says Dr. Steven Nissen, chairman of cardiovascular medicine at the Cleveland Clinic. “No intervention produces benefits in 100 percent of subjects. Biological systems are complex and many other factors can alter the response to any intervention.”

To be fair, the authors of this latest study start their paper by saying that: “Physical activity level and cardio-respiratory fitness are strong and inversely associated with risk of cardiovascular, metabolic, and aging related morbidities as well as premature mortality.”  In other words, as we have heard for decades, exercise is good for you in many ways.

All the studies they looked at took place over a few weeks or months and none of the outcomes measured actual disease or death.   Emphasizing the 10 percent who had negative outcomes in some risk measures hardly negates the benefits of exercise.

So if you’re looking for an excuse to stay away from the gym, this research isn’t it.

Robert Bazell is NBC's chief science and medical correspondent. Follow him on Facebook and on Twitter @RobertBazellNBC

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