By any measure, Dave McGillivray is a paragon of lifelong fitness.

The longtime race director of the Boston Marathon and the TD Beach to Beacon 10K has finished 131 marathons and completed eight Ironman triathlons. He once ran 3,452 miles from Oregon to Massachusetts to raise money for charity; another time he ran 1,520 miles from Florida to Boston. And each year on his birthday he runs the same number of miles as the years he’s been alive, a streak started when he was 12 years old.

So it came as a shock last October when McGillivray, 59, began gasping for air on routine runs.

“It felt like I was running at altitude,” he said. “I had this pain in my chest, and I’d run, walk, run, then walk until I could run aerobically without having to stop and catch my breath.”

Eventually the discomfort subsided, and he finished his workouts without a problem. But the breathlessness returned at the start of every run.

At first, McGillivray dismissed the symptoms as overtraining, overuse or maybe just a virus. After all, at routine checkups he always got a clean bill of health.

But the problems persisted, so he went in for tests. Blood tests, an electrocardiogram and a stress test turned up nothing. But an angiogram revealed something ghastly: One artery was 70 percent blocked, another was 40 percent blocked and a third artery was 50 percent blocked. McGillivray had coronary heart disease.

“I was shocked,” he said. “Sitting there on the exam table, seeing the blocked arteries on the video monitor, I thought, ‘This is the beginning of the end. I’m going to die.’ ”

DIFFERENCE BETWEEN FITNESS, HEALTH

Actually, the diagnosis was the beginning of something else entirely for McGillivray. Namely, a raft of diet and lifestyle changes that took 27 pounds off his 5-foot-4 frame, 80 points off his cholesterol level, and rendered him stronger, faster and more energized than he’s been in years.

The North Andover, Massachusetts, resident is still a few weeks away from tests that will show what impact the changes had on his arteries. But his story illustrates an important difference between fitness and health that doctors hope runners will take to heart.

“A daily exercise routine, and running in particular, is an incredibly powerful way to reduce the risk of a heart problem, but it does not completely confer immunity, and Dave is a perfect example of that,” said Aaron Baggish, associate director of the Cardiovascular Performance Program at the Massachusetts General Hospital Heart Center.

“There’s a common misconception that just because you’re fit and you run, you don’t have to worry about routine risk factors like the rest of the population – things like high blood pressure, high cholesterol, poor diet and genetics.”

McGillivray will be sharing his story and addressing this issue Thursday at a sports medicine symposium conducted by Beach to Beacon medical personnel. The event, at the Dana Center Auditorium at Maine Medical Center from 5 to 8 p.m., is free and open to the public.

To be sure, McGillivray is hardly the first runner to discover heart issues. In 2007, at age 48, coach and former Boston Marathon champion Alberto Salazar had a heart attack while out on a run. And then there is Jim Fixx, a former two-pack-a-day smoker with a family history of heart disease. He became a runner and wrote The Complete Book of Running, which is largely credited with inspiring the 1970s running boom. Fixx died at age 52 while out on a run in 1984.

And as a tidal wave of people have taken up running in recent years – a record 19 million people finished races in 2013, according to Running USA, up 22 percent from the year before – several finish-line deaths have grabbed media attention.

All of this has led medical experts and anyone looking for an excuse not to exercise to ask: Will running kill you?

Doctors are quick to answer with an emphatic “no.”

The American College of Sports Medicine recommends that most healthy adults get at least 150 minutes of exercise per week (five sessions of 30 minutes) to prevent chronic diseases. Running is considered one of the best forms of exercise because it’s cheap, convenient and requires no special equipment. Even a slow-paced jog can improve health measurably.

But those who exercise without eating right or managing their blood pressure, cholesterol and stress levels could be asking for trouble.

“Even if you’re running regularly, if you’re not addressing the routine things that cause heart disease, you’re going to end up with a problem at some point or another,” Baggish said. “A lot of runners eat whatever they want, thinking that running will keep weight down. But weight is just one part of the story. Having a lean body is not the same thing as having a healthy one.”

UNHEALTHY HABITS OUT THE WINDOW

Indeed, McGillivray had a raft of risk factors for heart disease that could have killed him had he not been so fit.

Heart disease runs in McGillivray’s family; his father had five-way bypass surgery and both grandfathers had heart attacks. And he is the first to admit that his diet, sleep patterns and stress levels were out of whack. He was always one of those people who figured sleep and recovery were overrated, and that he was entitled to a beer, a steak and a pint of ice cream for all of his hard work on the road.

As soon as he got the diagnosis, all that changed.

Sugar, red meat, fats, fried food and beers were out; fruits, vegetables and whole grains were in.

Doctors told him he didn’t have to be so austere, but he wanted to go all out. “I don’t need to put anything in my body that’s counterproductive,” he said. “It wasn’t tough to give up cookies or ice cream. It was a matter of life or death.”

What’s more, cleaning up his diet and dropping from 155 pounds to 128 set off a cascade of positive side effects that dramatically improved his quality of life.

“Because I lost weight, I felt better, and because I felt better, I could run better, and because I ran more, I lost more weight,” he said. “Now I feel as fit as I’ve been in 20 years. My energy level is as high as it’s ever been, And that feeds on the emotions and psyche, and makes you feel even better about yourself.”

He’s focused on sleeping more and taking more time to recover. He tries to feel a little less sheepish about taking time to exercise, knowing that staying healthy is what will help him take care of his loved ones.

“Before, I always snuck out the door for a run and felt guilty that I wasn’t doing something with my kids,” said the father of five. “Now I realize that if I take care of myself, I put myself into a better position to be around for a long time for them.”

McGillivray logs about 50 miles a week, and is planning his annual birthday run in August; this year it will be 60 miles. He’s eyeing an Ironman triathlon in October.

And he’s become passionate about sharing his story and the lessons he’s learned with other runners.

“Being fit doesn’t necessarily mean being healthy, and it took me 59 years to learn that,” McGillivray said. “It was a rude awakening.”

Jennifer Van Allen can be contacted at 791-6313 or at:

jvanallen@pressherald.com