"Even after people have hit adulthood with some unhealthy behaviors, it's not too late to produce a benefit for their heart if they change those behaviors," said study author Bonnie Spring, a health psychologist and professor of preventive medicine at Northwestern University Feinberg School of Medicine.
"Conversely, if they don't keep up their healthy lifestyle behaviors, and lose some, we will see adverse effects on their coronary arteries, which increases the risk of heart disease," Spring said.
While many studies have shown that unhealthy behaviors are linked with heart problems, fewer studies have looked at whether turning around the bad habits might have a good effect, she noted.
The general thinking is that people won't change, Spring added. She found that's not always true -- and that the change made a difference.
"What's important here is, if you have reached adulthood and you have an unhealthy lifestyle, you are not doomed to have heart disease," Spring said. "If you make healthy changes, you can reduce your risk."
Spring's team tracked the health behaviors of more than 3,500 men and women enrolled in the Coronary Artery Risk Development in Young Adults (CARDIA) study. The researchers evaluated the participants when they were aged 18 to 30 and then again 20 years later, looking for changes that predict heart disease, such as calcification in the blood vessels.
The investigators looked at five healthy habits: not being overweight; being a nonsmoker; being physical active; having a low intake of alcohol; and having a healthy diet (defined as being low in fat and high in calcium, fiber and potassium).
At the study's start, less than 10 percent of the young men and women reported all five healthy habits. Over time, 25 percent of the men and women made healthy lifestyle changes. About 35 percent stayed the same in terms of health habits, and 40 percent had fewer healthy habits over time.
The more healthy habits that were added, the lower the risk of heart disease, the researchers found. "We can't claim cause-and-effect," Spring said, because the study only found an association between the two.
However, the more healthy habits that were added, the lower the risk of finding the early signs of heart problems, she explained. The more that were discarded, the higher the risk.
For instance, those who kept the same habits over the 20 years had nearly a 20 percent risk of having the early signs of heart disease by year 20. Those who discarded three or four healthy behaviors had a 32 percent risk of having the early heart disease signs. And those who added three or four healthy habits reduced the risk to just 5 percent.
What to do first? The two habits that had the most effect, Spring said, were keeping a healthy weight and not smoking.
Those two habits might have shown the greatest effect simply because they are easier to measure, Spring said. Even so, she suggested those two habits are a good place to start.
The study is published in the July 1 issue of the journal Circulation and was funded by the U.S. National Institutes of Health.
One expert noted the study shows that lifestyle choices made early in adulthood may make all the difference.
"This new study provides new insight into how lifestyle changes from ages 18 to 30 play out over the next 20 years," said Dr. Gregg Fonarow, professor of cardiovascular medicine and science at the David Geffen School of Medicine at the University of California, Los Angeles.
While much research has shown how unhealthy habits add to the risk of heart problems, Fonarow said, "it has not been well studied to determine how changes in lifestyle in early adulthood impact subsequent development of atherosclerosis [hardening of the arteries] and cardiovascular risk."
The findings, he said, "suggest it is never too early to adopt a healthy lifestyle but that even those who start off on the wrong path can substantially turn their cardiovascular risk around by making favorable lifestyle choices in early adulthood."
To learn more about how modest changes can make a difference, visit the American Heart Association.