Exercise linked to health risks in some, but experts urge not to avoid

By Deborah Kotz, Globe Staff

As reluctant as Americans are to hit the gym -- only 20 percent of us meet the government’s exercise recommendations -- it may get even tougher to convince them thanks to a new study suggesting that workouts may increase heart risks in a small percentage of people. But a Boston exercise specialist not involved in the study said the new finding shouldn’t be used as an excuse to avoid getting fit.

The research, published online in the journal PLoS One and conducted by well-respected scientists in the fitness field, analyzed six exercise trials involving a total of nearly 1,700 healthy sedentary adults and found that within a few months, about 7 percent of those who began exercising had a worsening of two heart disease risk factors, such as an increase in blood pressure or triglycerides, a “bad” component of cholesterol, or a decrease in HDL cholesterol --which normally rises during exercise -- or insulin sensitivity, a diabetes indicator. (Most of the participants in the studies had improvement in these risk factors.)

“That’s not a good sign,” said study leader Dr. Claude Bouchard, an obesity researcher at the Pennington Biomedical Research Center in Baton Rouge, La. “I suspect the most important explanation here will be genomics.”

Unfortunately, he and others haven’t yet identified specific gene variations to predict which people will be more likely to experience detrimental effects from exercise. That, Bouchard said, is the next area for research and could eventually lead to a personalized medicine approach with doctors prescribing different types of exercise, say, strength training or yoga moves over running for those with certain genetic predispositions.

In the meantime, should some people avoid exercise altogether? And if so, who are those folks?

“This is a complex issue and the most critical one, but we don’t have all the answers,” Bouchard admitted. If you’re already exercising and doing well on your training regimen, keep at it, he advised.

If you’re sedentary and about to start an exercise program, you might want to get your blood pressure, cholesterol levels, or blood glucose levels checked a bit more frequently, Bouchard added, especially if they’re already a little elevated. “You want to see if exercise moves these numbers in the wrong direction.”

Other experts not involved in the study, however, say it’s foolish to warn healthy people away from exercise. “If we think about all the medications and interventions out there, exercise outperforms them all for reducing heart disease risk in terms of improving blood pressure, insulin sensitivity, and cholesterol,” said Dr. Gregory Lewis, associate director of the cardiopulmonary exercise laboratory at Massachusetts General Hospital.

That’s true, he said, for the vast majority of people who go from doing nothing to doing something that gets them sweating a few days a week. What’s more, exercise has mood-boosting, anti-depressant-like effects and builds our muscles and bones to keep us mobile and agile as we age.

While Lewis called the study “well done,” he also said it had an inherent limitation in that exercise wasn’t introduced in a vacuum with everything else kept constant. For instance, it’s impossible to know whether study participants gave themselves an extra scoop of ice cream or serving of pasta every time they exercised -- which could led to a net surplus of calories resulting from the exercise plan.

Bouchard dismissed this concern, pointing out that the studies controlled for this by asking participants to fill out dietary surveys before and during the study.

Still, people have been known to fudge these questionnaires, and a growing body of research suggests that exercise alone doesn’t lead to weight loss often because people get hungrier and eat more after their workouts. It does, though, lead to accelerated weight loss when used in conjunction with a calorie-reduced eating plan.

No question, more research is needed to “learn more about how exercise affects individuals,” Lewis said, since it’s well established that each of us responds differently to the same levels of exercise, with some of us developing larger improvements in lung capacity (a sign of physical fitness) than others.

In the meantime, Lewis stressed that people shouldn’t be scared away from exercising. “This isn’t the first time that an adverse effect of exercise has been discovered,” he said. “People can get rare arrhythmias and suffer heart attacks when running, but we also know that running prevents a lot more heart attacks than it causes.”

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.