A Daily news digest by Jasper van Santen

For Some, Exercise May Increase Heart Risk – NYTimes.com

In News on May 31, 2012 at 03:52

For Some, Exercise May Increase Heart Risk

Intuitively this sounds a little ridiculous.

Could exercise actually be bad for some healthy people? A well-known group of researchers, including one who helped write the scientific paper justifying national guidelines that promote exercise for all, say the answer may be a qualified yes.

By analyzing data from six rigorous exercise studies involving 1,687 people, the group found that about 10 percent actually got worse on at least one of the measures related to heart disease:blood pressure and levels of insulin, HDL cholesterolortriglycerides. About 7 percent got worse on at least two measures. And the researchers say they do not know why.

“It is bizarre,” said Claude Bouchard, lead author of the paper, published on Wednesday in the journal PLoS One, and a professor of genetics and nutrition at the Pennington Biomedical Research Center, part of the Louisiana State University system.

Dr. Michael Lauer, director of the Division of Cardiovascular Sciences at the National Heart, Lung, and Blood Institute, the lead federal research institute on heart disease and strokes, was among the experts not involved in the provocative study who applauded it. “It is an interesting and well-done study,” he said.

Others worried about its consequences.

“There are a lot of people out there looking for any excuse not to exercise,” said William Haskell, emeritus professor of medicine at the Stanford Prevention Research Center. “This might be an excuse for them to say, ‘Oh, I must be one of those 10 percent.’ ”

But counterbalancing the 10 percent who got worse were about the same proportion who had an exaggeratedly good response on at least one measure. Others had responses ranging from little or no change up to big changes, seen in about 10 percent, where risk factor measurements improved anywhere from 20 percent to 50 percent.

“That should make folks happy,” said Dr. William E. Kraus, a co-author of the study who is a professor of medicine and director of clinical research at Duke. He was a member of the committee providing the scientific overview for the Department of Health and Human Services’ national exercise guidelines, which advise moderate exercise for at least 150 minutes a week.

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.

“You can’t have it both ways,” Dr. Bouchard said.

The national guidelines for exercise are based on such inferences and also on studies that compared the health of people who exercised with that of people who did not, a weak form of evidence often said to be hypothesis-generating rather than proof.

“We do not know whether implementing exercise programs for unfit people assures better outcomes,” said Dr. Lauer of the heart institute. “That has not been established.” And so, he said, “there is a lot of debate over how strong the guidelines should be in light of weak evidence.”

 

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