In a new 20-year study, women who led a healthy lifestyle in their young adult years were 92 percent less likely than those who didn’t to develop heart disease by middle age.

U.S. researchers followed thousands of women starting in their 20s and 30s and found those with healthy diet and exercise habits, who didn’t smoke, were also 66 percent less likely to have any heart risk factors like diabetes or hypertension by the time they were in their 40s and 50s.

The results suggest that more than 70 percent of heart attacks in younger women could potentially be prevented by changes in lifestyle, the authors conclude.

“As somebody who is currently in her 30s, I think a lot of us think that we are invincible at this point and we don't have to worry about things like heart attacks until we get old,” said Andrea Chomistek, who led the study.

“I think this study shows that we should be thinking about things like this early on,” said Chomistek, of the Indiana University School of Public Health in Bloomington.

Chomistek said most research on heart disease risk factors has focused on older people because they’re typically the ones who have heart attacks.

"There's not a whole lot of information out there for younger people," she told Reuters Health.

Rates of death from heart attacks among older people have dropped steadily over the past 40 years, but death rates among younger women have actually increased slightly during that time, Chomistek and her colleagues point out in the Journal of the American College of Cardiology.

They analyzed data from The Nurses’ Health Study II, which includes survey responses for more than 70,000 women who were between the ages of 25 and 42 years old in 1991.

Tracking the women until 2011, the study team looked for six healthy habits: not smoking, watching less than seven hours of TV per week, drinking no more than one alcoholic beverage per day, getting at least 2.5 hours of exercise per week, eating a healthy diet and maintaining a normal body weight.

At the end of 20 years, a total of 456 women had heart attacks. Almost 32,000 women were diagnosed with one or more cardiovascular disease risk factors, including type 2 diabetes, high blood pressure or high levels of cholesterol.

The average age of a heart disease diagnosis was 50 years old, and the average age for diagnosis with a cardiovascular risk factor was about 47 years old.

The researchers found that compared to women with none of the healthy lifestyle habits, women who had all six healthy habits were 92 percent less likely to have a heart attack.

After accounting for the other healthy habits, the hours of television women watched were not linked to their heart disease risk.

Heavy alcohol intake was linked to greater heart risk, but the lowest risk was seen with average consumption of about 5 to 15 grams of alcohol a day, the equivalent of approximately 5 ounces of wine, 12 ounces of beer or 1.5 ounces of spirits.

“Though we didn't have that many cases of heart disease for the study, over half the women developed one of the cardiovascular risk factors - either hypertension diabetes or high cholesterol - so that wasn't rare at all, even among this younger group of women," Chomistek said.

But, Chomistek added, maintaining a healthy lifestyle was still important for preventing future heart disease in those women who had one or more risk factors.

“Once you develop a risk factor it's not too late to start improving your lifestyle and trying to get things going in right direction,” she said.

Dr. Annie Kelly, a cardiologist at the University of Wisconsin in Madison, said it’s a landmark study because it not only focuses on women, but young women in particular. She was not involved in the research.

Kelly said that awareness about women and heart disease is fairly new, noting that the American Heart Association’s “Go Red for Women” campaign wasn’t started until the early 2000s.

“This is a disease process that develops over time and you may look and feel healthy now but we worry about your risk in the future,” she told Reuters Health.

Kelly said that young women are often “super busy” and may not take care of themselves properly, but the study makes it clear that they need to focus on their health.

“It's not selfish, so get rid of the guilt,” Kelly said. “This will sustain you with the promise of a healthier and more productive future and then these habits will also be passed on to your children.”