Young adults who can run 3000 meters faster tend to have thinner artery walls in their necks, which is a sign of less early artery damage, even if they’re overweight or have other risk factors.

Whether young adults are normal weight or overweight, better fitness is just as strongly linked to thinner artery walls — meaning being fit helps your arteries even if you carry extra weight.

In young men, being fitter and having lower triglycerides both link to healthier arteries, but in young women, only fitness matters — triglycerides don’t seem to affect artery thickness in this group.

People who are more physically fit in their 60s tend to have lower pressure in their main arteries, more flexible blood vessels, and less stress on their heart—signs their blood vessels are younger and healthier.

Among young, active adults, high levels of triglycerides (a type of fat in the blood) are the only blood marker that consistently links to thicker artery walls — more than cholesterol, blood sugar, or belly fat.