Every 15 percent increase in aerobic fitness in your teen years is associated with an 18 percent reduced risk of heart attack three decades later, researchers report in the Jan. 8 online edition of the European Heart Journal.
The results also suggest that teens and young adults who undergo regular cardiovascular training have a 35 percent reduced risk of heart attack later in life.
Aerobic fitness as a teen even appears to help people who become obese later in life, said research leader Peter Nordstrom, of Umea University in Sweden.
"It should be noted that aerobic fitness decreased the risk of heart attack significantly within also overweight and obese men," Nordstrom said. Obese men who had the highest aerobic fitness as teens enjoyed a 60 percent lower risk of heart attack compared with obese men who had the least fitness.
However, obese men with high aerobic fitness did have a higher risk of heart attack than lean men with little aerobic fitness. While the study found an association between aerobic fitness and chances of heart trouble, it did not establish a cause-and-effect relationship.
The findings emphasize the need for improved physical fitness among young people, said Dr. Stephen Daniels, chairman of pediatrics at the University of Colorado School of Medicine and a spokesman for the American Heart Association.
"Even though the diseases we see are diseases of older adults, it's increasingly clear that where people are in childhood and adolescence is critically important," Daniels said. "We probably aren't doing enough to help our young population become fit and avoid obesity."
For the study, the researchers analyzed medical data from 743,498 men drafted into the Swedish army at age 18 between 1969 and 1984.
As a part of induction, all of the draftees took part in a physical examination that included a test of their aerobic fitness. They all had to ride on an exercise bicycle until they were too exhausted to continue.
National health registers provided information on heart attacks the men suffered later in life. Doctors used this medical data to track men for an average 34 years following their military physical exam.
The researchers found that men with the lowest aerobic fitness had a more than twofold increased risk of later heart attack compared with men who were most fit.
The study authors also looked into the joint effect of obesity and fitness, and found that across all weight groups the risk of a later heart attack increased significantly when comparing the least fit with the most fit.
However, the fittest obese men ran a 71 percent increased risk of heart attack when compared to men who were unfit but lean. They also had more than four times the heart attack risk faced by the fittest lean men.
"This study helps to address the 'fitness versus fatness' question by indicating that both are important, but they are independently important," Daniels said. "Good fitness can't completely counterbalance the health effects of excess weight. Obviously, the best is to be normal weight and fit, which is what we should be aiming at for the majority of our population."
Muscle strength, which also was tested during induction, did not appear to provide the same heart health benefits as aerobic fitness.
Genetics likely plays a large part in the aerobic fitness of teens and, by extension, their protection against heart attack, Nordstrom said. Another study that focused on twins within this same set of patients found that 78 percent of the variation in their aerobic fitness could be chalked up to genetics.
But it could also be that men who are in good shape in their teens have adopted the sort of lifestyle that will keep them healthy later in life, said Dr. Mark Urman, a member of the American College of Cardiology's Prevention of Cardiovascular Disease Committee.
"If you're fit as a teenager, you're going to be more likely to stay in shape over the course of your life," Urman said. "The better shape you're in, the less apt you are to have cardiovascular problems."
For more information on children and physical fitness, visit the U.S. Centers for Disease Control and Prevention.