New research suggests that high levels of exercise can help slow the aging within the cells significantly.

Researchers from Brigham Young University have found that people who regularly partake in intense exercise have longer telomeres, reducing aging at the cellular level by up to nine years.

“Just because you’re 40, doesn’t mean you’re 40 years old biologically,” exercise science professor Larry Tucker, said in a statement. “We all know people that seem younger than their actual age. The more physically active we are, the less biological aging takes place in our bodies.”

Telomeres—protein endcaps on chromosomes—act as a biological clock for humans. They are correlated with age as each time a cell replicates a small portion of the endcap is lost.

Tucker said adults with higher physical activity levels have telomeres with a biological aging advantage of nine years over those who are sedentary, and a seven-year advantage over those who are moderately active.

“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. “You have to work out regularly at high levels.”

Tucker said telomere length is likely tied to inflammation and oxidation stress, which explains why it decreases without strenuous exercise.

“We know that regular physical activity helps to reduce mortality and prolong life, and now we know part of that advantage may be due to the preservation of telomeres,” Tucker said.

Highly active exercise is considered 30 minutes of jogging for women five days a week or 40 minutes for men.

Tucker examined data from 5,823 adults who participated in the Centers for Disease Control and Prevention’s National Health and Nutrition Examination Survey, which included an index of data for 62 activities participants might have engaged in over a 30-day period.

Tucker said sedentary people had 140 base pairs of DNA less at the end of their telomeres than highly active people. However, Tucker also found that there was no significant difference in telomere length between those who participate in low or moderate physical activity and sedentary people.

The study was published in Science Direct.