DALLAS — Dr. Chip Lavie says he has to wear body armor to races these days because of hostility from fellow runners, and he sounds like he’s only partially kidding.

The medical director of cardiac rehabilitation and preventive cardiology at John Ochsner Heart and Vascular Institute in New Orleans is also is co-author of two recent studies about running’s potentially negative effects on the heart.

“People have written in heavily criticizing it,” he says. “Obviously it’s made people think.”

The essence of the studies is of the good-news, bad-news ilk.

Good news: Runners have a 20 percent lower mortality rate than nonrunners.

Bad news: People who run in higher doses — more than 20 miles per week — seem to lose that benefit.

“I thought you’d have lower mortality with running and at some point it would level off, and there would be no additional benefit,” he says. “But I didn’t think it would level off and head the other way. There actually seems to be a U-shape.

“At superhigh doses — marathon running, ultra-marathons, really long-distance bike races — there’s actually potential for cardiac harm.”

Publications have had a track-and-field day with headlines like these: “One Running Shoe in the Grave” (The Wall Street Journal). “Forget agony of the feet: Running marathons may wreck your heart” (MSN Now). And this from an editorial in the British journal Heart: “Running too fast, too far and for too many years may speed one’s progress toward the finish line of life.”

Though his own research has made Lavie, whose marathon personal best is an impressive 3:10, cut back a little, he still runs almost daily (except one day before a short race and two before a long one). As of right now, he’s sticking with 5Ks, 10Ks and half marathons — not full.

“I’m not trying to scare people,” he says. “I’m more interested in encouraging people to get the maximum benefit at lower levels. From a society standpoint, there’s much more of a problem with lack of exercise than too much.”

That seems to be the crux of local experts’ message, too.

“First of all, we shouldn’t use those studies as a reason not to exercise,” says Dr. Sarah Samaan, a cardiologist at Legacy Heart Center and Baylor Heart Hospital Plano. “Exercise absolutely lowers the risk of heart attack, stroke and dementia by 30 percent.”

Still, she says, “If you do marathons, understand there can be risks involved with the heart. If you’re going to train, do so in a systematic way.”

Dr. Kenneth Cooper, whose running life spanned 44 years and 38,000 miles, says he’s much more concerned with obesity and inactivity than “an isolated case of someone running and dying.

“Death doesn’t occur that much,” says Cooper, who is 81 and now walks regularly. “The chance of dying while exercising is remarkably low. You’ll have deaths doing anything — watching football even. The value of exercise is overwhelming compared to the risk, but more isn’t always better.”

Intensity is the key word. “Think if you try to do weights and do a heavy one that’s 10 or 15 pounds heavier, what if you lifted it 150, 200 times?” he says. “You’d almost not be able to move the next day. In a way, that’s what you’re doing in a marathon to the heart muscle. It’s one thing if you’re doing it for 30, 40 minutes, but another for many hours straight.”