A 20-year study of nearly 70,000 women suggests that lifestyle factors impact heart attack risk in early adulthood.

“We noticed that overall mortality trends from heart disease have declined over the past few decades, but the trends among younger adults— and particularly women— were actually increasing by 1 or 2 percent … and there weren’t a lot of studies out there with data on young women,” lead study author Andrea Chomistek, professor of epidemiology and biostatistics at Indiana University, told FoxNews.com.

Chomistek and other study authors at Indiana University, the Harvard School of Public Health, and Brigham and Women’s Hospital analyzed data on 69,247 women with an average age of about 37.

Researchers monitored the women’s instances of heart attack and cardiovascular disease factors such as type 2 diabetes, and high levels of blood pressure and cholesterol. They compared these data against whether the participants reported following six healthy habits known to affect heart disease risk. Those habits consisted of not smoking, maintaining a normal body mass index (BMI), exercising at least two and a half hours a week, watching seven or fewer hours of TV a week, consuming an average of no more than one alcoholic beverage a day, and maintaining a healthy diet.

Over the course of the study, 456 women had heart attacks, and nearly 32,000 women were diagnosed with at least one heart disease risk factor. On average, the women who were diagnosed with heart disease had an average age of about 50, while the average age of those women who developed a heart disease risk factor was about 47.

Women who followed all six healthy habits had a 92 percent lower risk of heart attack and a 66 percent lower risk of developing a heart disease risk factor. These data suggest that three-fourths of heart attacks and almost half of the incidents of these risk factors in young women could have been prevented if the women had followed all of the healthy habits, the study authors wrote.

According to the Centers for Disease Control and Prevention (CDC), heart disease is the leading cause of death for men and women in the United States. About 600,000 people die of heart disease in the U.S. every year, making the condition responsible for one in four deaths in the country.

In the study, an unhealthy BMI was the greatest predictor of heart disease, Chomistek said. BMI is a number calculated from a person’s weight and height, and it correlates to direct measures of body fat. A normal BMI for adults ranges between 18.5 and 24.9, according to the CDC.

Not smoking, adequate physical activity and a healthy diet were also all independent factors that decreased a woman’s risk of developing heart disease.

The researchers measured a healthy diet based on the Harvard School of Public Health’s Healthy Eating Plate, which recommends that half of a person’s plate during any given meal consist of fruits and vegetables, one-quarter of whole grains, and the other quarter of versatile protein including nuts, beans, fish, and chicken.

Study participants who consumed an average of about one alcoholic drink per day had the lowest risk compared to those who drank more or didn’t drink at all.

Chomistek said a significant finding was that even those women who were taking medication to treat a heart disease risk factor saw their health affected by their lifestyle choices.

“I think a lot of people think, ‘If I’m taking my blood pressure or cholesterol medication, then I don’t need to exercise and eat healthy,’” she said. ‘People think they’re invincible, like, ‘I don’t have to worry about my health until I’m old,’ but that’s not the case.”

The study was published Monday in the Journal of the American College of Cardiology.