Compared with the people in the study who didn't exercise at all, the highly active people had a "biological age" that was about nine years younger, said study author Larry Tucker, a professor of exercise science at Brigham Young University in Utah.
To reap these benefits of exercise, you'd need to spend 30 to 40 minutes running, five days a week, according to the study.
In the study, Tucker looked at data on more than 5,800 people ages 20 to 84 who had taken part in a health survey conducted by the Centers for Disease Control and Prevention. The survey, called National Health and Nutrition Examination Survey, is aimed at collecting data on people's lifestyle, health, physical activity and nutrition. [How to Jump-Start Your Exercise Routine in 2017]
In addition to filling out questionnaires, the people who had participated in the survey had samples of their DNA collected by CDC investigators between 1999 and 2002.
The purpose of this DNA collection was to measure the lengths of people's telomeres, which are molecular "caps" found on the ends of chromosomes that protect the genetic structures from damage. Telomeres get shorter over time, but the rates of this shortening vary from person to person. Therefore, telomeres are considered a marker of a person's "biological age," which refers to the age of that person's cells rather than his or her chronological age.
Although the CDC survey had data on both physical activity levels and telomere length, the relationship between the two had not been analyzed.
In the study, Tucker looked into this relationship, and found that the people who had high physical activity levels had significantly longer telomeres than the people who did not exercise at all and the people who exercised less frequently and less intensely.
In particular, the men in the study who exercised at the intensity and duration equivalent to 40 minutes of running five days a week, and the women who exercised at the equivalent of 30 minutes of running five days a week, had telomeres whose length suggested their cells were nine years younger than the cells of the people who did not exercise at all.
Tucker also compared the telomere length of the people in the highly active group with the telomere length of the people who also exercised but at lower levels. In this case, he found that the difference in cellular aging between the two groups was seven years. [Extending Life: 7 Ways to Live Past 100]
This finding suggests that "for telomeres, taking it to the next level of activity seems important," Tucker told Live Science.
In other words, "If you want to see a real difference in slowing your biological aging, it appears that a little exercise won't cut it,” Tucker said in a statement. "You have to work out regularly at high levels."
It is not clear why being highly active is linked to having longer telomeres, but previous research has shown that exercise may help reduce inflammation and oxidative stress, both of which have been implicated in the more rapid shortening of telomeres, Tucker said.
A previous study found that professional athletes had higher levels of activation of an enzyme called telomerase, which stabilizes telomeres, compared with people who didn't exercise.
Originally published on Live Science.