Inactivity is the biggest heart disease risk factor for women over 30

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For women over age 30, lack of physical activity is a more important contributor to the risk of heart disease than being overweight, smoking or having high blood pressure, a new study from Australia suggests.

The findings suggest that more should be done to promote physical activity at all ages, because it tends to receive less attention than other lifestyle recommendations like quitting smoking and losing weight, the researchers said.

The researchers analyzed information from more than 32,000 Australian women from three age groups 22 to 27, 47 to 52 and 73 to 78 who were followed for 12 years. The women answered questions about their physical activity, smoking habits, weight and whether they had ever been diagnosed with high blood pressure. [10 Amazing Facts About Your Heart]

For women under age 30, smoking had the biggest impact on heart disease risk: Eliminating smoking would prevent nearly 60 percent of heart disease cases in this age group, the study found.

But after age 30, lack of physical activity was the biggest contributor. Eliminating physical inactivity would prevent 33 percent of heart disease cases among middle-age women, and 24 percent of heart disease cases among older women. In contrast, eliminating smoking would prevent about 15 percent of cases of heart disease for women in their 60s, and 5 percent for women in their 70s.

The researchers used a mathematical formula to determine the percentage of heart disease cases that would be prevented if certain risk factors did not exist (including smoking, being overweight, being relatively inactive or having high blood pressure). This calculation included information about how common these risk factors were, and the likelihood that women with each of these risk factors would develop heart disease, compared with someone without the risk factor.

Although doctors may ask patients about their family history of heart disease, or check them for other risk factors, they typically don't ask about physical activity, said Dr. Martha Gulati, director of Preventive Cardiology and Womens Cardiovascular Health at Ohio State University's Wexner Medical Center, who was not involved in the study. "It's an under-recognized risk factor," Gulati said. "Assessing someone's fitness or physical activity should be something that we do more of."

Some studies show that people's risk of dying over a certain time period goes down if they are physically active, regardless of whether they are overweight, Gulati said.

It's important to note that the study findings largely reflect how common the individual risk factors are at certain ages. For example, smoking becomes a less important risk factor over time because fewer women smoke as they age, whereas more women become inactive with age, said study researcher Wendy Brown, a professor of physical activity and public health at the University of Queensland.

So the most important risk factor for a given woman depends on her lifestyle and other factors.

The study only looked at the four top risk factors for heart disease in Australia, and did not consider other risk factors, such as poor diet.

The findings may apply to women in other countries with similar patterns of behavior, such as Canada and Western Europe, Brown said.

The study was published online May 8 in the British Journal of Sports Medicine.