Is Exercise Harmful for Some People?

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For some healthy people, exercise may actually increase heart risk, according to a paper published this week in the journal PLoS One.

The review of six previous studies on exercise found that working out worsened at least one measure of heart risk — blood pressure, insulin level or levels of HDL cholesterol or triglycerides — for about 10% of people. About 7% of people declined on at least two measures.

The lead author of the paper, Claude Bouchard, a professor of genetics and nutrition at the Pennington Biomedical Research Center at Louisiana State University, told the New York Times that the finding was “bizarre.”

(MORE: 5 Mistakes You’re Making at the Gym)

At the same time, the data, involving 1,687 people, showed that about 10% of people saw outsized gains in at least one measure of heart disease risk — some patients improved 20% to 50%. For other participants, exercise-related rewards ran the gamut, from none to some to significant benefits.

One of the authors of the study was on the committee that provided the scientific evidence underlying the government’s official exercise guidelines for Americans, which recommend at least 150 minutes per week of moderate activity.

The implication here is that the government’s physical activity guidelines are based on rather weak scientific data. The Times’ Gina Kolata writes:

The problem with studies of exercise and health, researchers point out, is that while they often measure things like blood pressure or insulin levels, they do not follow people long enough to see if improvements translate into fewer heart attacks or longer lives. Instead, researchers infer that such changes lead to better outcomes — something that may or may not be true.

Some critics have noted that there is no indication that those who had what Dr. Bouchard is calling an adverse response to exercise actually had more heart attacks or other bad health outcomes. But Dr. Bouchard said if people wanted to use changes in risk factors to infer that those who exercise are healthier, they could not then turn around and say there is no evidence of harm when the risk factor changes go in the wrong direction.

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Still, the findings are no excuse not to exercise. For one thing, it’s still not clear why some people had adverse responses to working out. The results couldn’t be explained by how fit participants were (or later became), how strenuously they exercised, whether they were taking medications for blood pressure or cholesterol, or their age, race or gender. “I suspect the most important explanation here will be genomics,” Bouchard told the Boston Globe.

Researchers said it’s important to figure out who will benefit from exercise and who won’t, if we want to able to prescribe exercise individually for better health. “Identifying the predictors of such unwarranted responses and how to prevent them will provide the foundation for personalized exercise prescription,” they wrote.

But for healthy people, experts agree that exercise is a benefit overall. It improves mood, makes you stronger and preserves physical fitness as you age.

So, for now, the authors recommend that people continue exercising as before. If you’ve been sedentary and are starting a new exercise regimen, however, it would be a good idea to check in regularly with your physician to monitor measures of heart health.

MORE: When Mom Exercises in Pregnancy, Her Baby’s Heart Benefits

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