Scientists know plenty about heart health in middle and old age. But data on the cardiovascular health of young adults is more scant.

A new study in the journal Circulation sheds some light on this little-understood period — and shows it may be feasible to reduce the possibility of heart attacks and strokes even in people who start out with poor heart health.

The study used insurance data collected during routine health exams for 3.5 million young adults in South Korea between 2003 and 2004. Many received follow-up exams in the years that followed.

Researchers from Yonsei University College of Medicine in Seoul gave each patient a score based on six common measures of cardiovascular health: low cholesterol, a healthy weight, participation in physical activity, under-control blood sugar and blood pressure, and nonsmoker status. Then they looked to see how many people were hospitalized for cardiovascular events such as heart attack or stroke.

The higher the heart-healthy score, the less likely participants were to be hospitalized for heart trouble. That isn’t surprising based on what scientists already know about the benefits of a heart-healthy lifestyle.

But you may be surprised by how big of an effect each cardiovascular health factor had. A one-point increase in the score was associated with a 42 percent reduction in heart attack risk and lower risk of heart failure and stroke. And patients who had lower scores but improved them over time managed to reduce their risk.

That has implications for doctors and patients. It suggests that while it’s best to start out with good heart health and healthy habits, gains are possible even for those who don’t have good heart health in young adulthood. It also implies that it’s worth monitoring heart health in young adults, even those who don’t have a history of cardiovascular events.

Unsurprisingly, the study found that people who began with good heart health and maintained it were least likely to be hospitalized or die of a stroke or heart attack. But even though young adults are less likely to have cardiovascular events, researchers say, it’s worth tracking them.