Being in shape may be as important to a long life as not smoking, according to an interesting new study of the links between fitness and mortality.
The study also explores whether there is any ceiling to the benefits of fitness — whether, in essence, you can exercise too much. The answer, it found, is a reassuring no.
At this point, we should not be surprised to hear that people who exercise and have high aerobic endurance tend to live longer than those who are sedentary and out of shape. A large body of past research has linked exercise with longevity and indicated that people who work out tend also to be people with lengthy, healthy lives.
But much of this research relied on asking people about their exercise routines, a practice that is known to elicit unreliable answers.
So for the new study, which was published this month in JAMA Network Open, a group of researchers and physicians at the Cleveland Clinic decided to look for more objective ways to measure the relationship between endurance and longevity.
Because most of the researchers also are avid exercisers and even competitive athletes, they hoped to learn, too, whether people can overdo exercise and potentially shorten their life spans.
Helpfully, they had a trove of data at hand in the records of hundreds of thousands of men and women who had completed treadmill stress tests at the clinic.
These stress tests, which sometimes are part of standard yearly checkups and other times are ordered by physicians to check for cardiac or other health problems, involve someone jogging on a treadmill at a progressively intense pace until, basically, he or she cannot.
Based on the results, technicians can determine people’s aerobic fitness.
Now, the researchers turned to this database and pulled records for 122,007 middle-aged or older men and women.
They grouped the people by fitness, from those who were in the bottom quarter of fitness, to those who were below average, above average or highly fit, essentially in the top 25 percent of fitness.
The researchers also marked off a small group in the top 2 percent or so of endurance and categorized them as having “elite” fitness.
Then the researchers checked death records for the decade after people had completed their stress tests.
They found that some of the men and women had died and also that there strong correlations between fitness and mortality.
The greater someone’s fitness, the less likely he or she was to have died prematurely and vice versa, the numbers showed.
This correlation held true at every level of fitness, the researchers found. People with the lowest fitness were more likely to die early than those with below-average fitness, while those with high fitness lived longer than those whose fitness was above average.
Even at the loftiest reaches of endurance, the advantage held, the data showed. The 2 percent of the people with elite fitness lived longer than those with high fitness and were about 80 percent less likely to die prematurely than the men and women with the lowest endurance.
“We did not see any indication that you can be too fit,” says Dr. Wael Jaber, the study’s senior author and a cardiologist at the Cleveland Clinic Lerner College of Medicine.
More surprising, when the researchers compared the longevity benefits of endurance to those of other health factors, fitness held up well.
People in this database who smoked or had heart disease were more likely to die young than those who did not, the researchers found, as they had expected.
But the numerical risks were about the same as the ones associated with being unfit. In other words, being out of shape increased someone’s risk of dying early as much as smoking did.
But Dr. Jaber cautions that these numbers can be misinterpreted. The clinic’s medical records noted only if someone had ever smoked, not for how many years or how frequently, making risk assessments difficult.
The correlations also do not suggest that being fit somehow balances out or reduces the health risks of smoking, Dr. Jaber says. “Fitness is very good for you and so, obviously, is not smoking,” he says.
The study has other caveats, including the confounding role of genes, which strongly influence fitness. Some of the apparent longevity benefits of being in shape may be from having the right parents, Dr. Jaber says.
Socioeconomic status and other factors also probably play a role. People who show up for stress testing at the Cleveland Clinic may have resources that are not shared by everyone, including good insurance and an interest in health.
Perhaps most fundamentally, the study did not look directly at exercise, only fitness, and so cannot tell us how much we should move to extend our lives.
But the findings are tantalizing, Dr. Jaber says. “We know from other research that you can increase fitness with exercise,” he says. “So I think we can say, based on this study and others, that it is a very good idea to exercise if you hope for a long and healthy life.”