Heart disease, most often in the form of coronary artery disease (CAD), is the leading cause of death for both men and women in the United States. With CAD, narrowed coronary arteries reduce blood and oxygen flow to the heart muscle (a condition also known as myocardial ischemia ) and place a person at risk for heart attack and other cardiovascular events. On the bright side, many risk factors for heart disease are modifiable– overweight and physical inactivity being among them. Currently in the US, nearly two-thirds of adults are overweight and over one third are obese.

While “ obesity and overweight” and “sedentary lifestyle” are listed separately as risk factors for heart disease, weight and physical fitness are clearly interrelated. There has been little research, however, questioning exactly how these two variables independently affect the risk of heart disease. This prompted researchers to conduct the Women’s Ischemia Syndrome Evaluation (WISE), funded by the National Heart, Lung, and Blood Institute (NHLB).

The results of this study, published in the September 8, 2004 issue of the Journal of the American Medical Association , revealed that among women with suspected heart disease, higher physical fitness levels were associated with less obstruction of the coronary arteries and fewer cardiovascular events such as heart attack. At the same time, overweight levels were not significantly associated with either of these outcomes.

About the Study

WISE is the most comprehensive study to date of independent heart disease risks associated with obesity and physical activity. It was also the first to evaluate these risk factors in women who were already exhibiting symptoms of heart disease.

From 1996 to 2000, 936 women with chest discomfort, suspected ischemia, or both were enrolled in the WISE study at 4 academic medical centers. Obesity was measured by way of Body Mass Index (BMI), waist circumference, waist-hip ratio, and waist-height ratio. Physical fitness was measured both by self-report of fitness capacity, and by estimates of activity at home, work, and leisure.

Researchers also measured blockages in the subjects’ coronary arteries using a test called coronary angiography, which takes x-ray images as a dye passes through them. Finally, the researches gathered information on the incidence of adverse cardiovascular events through follow-up interviews with both patients and referring physicians for an average of four years. An adverse cardiovascular event was defined as death or hospitalization due to heart attack, stroke, congestive heart failure, or other vascular complications.

The Findings

Out of 906 participants, 76% were overweight (defined as having a BMI of over 25), and 70% had low scores on the fitness capacity questionnaire. As for presence of heart disease, 39% tested positive for blockages in their coronary arteries upon enrollment, and during follow-up, 51% experienced an adverse coronary event. Eight percent died.To isolate the impacts of overweight and physical inactivity on CAD, results were adjusted to account for other CAD risk factors such as age, diabetes, use of hormone therapy, blood pressure, cholesterol levels, blood sugar levels, previous smoking, and aspirin use. These adjustments significantly reduced the apparent affects of both obesity and physical fitness level on severity of heart disease.

After the adjustments, overweight women were more likely than normal weight women to have concurrant other coronary risk factors, but were not more likely to have coronary artery obstruction or to experience adverse coronary events. But women with lower physical fitness scores were more likely to have other coronary risk factors and coronary artery obstruction. Furthermore, as their physical fitness level increased, there risk of adverse coronary events decreased. Thus, a stronger protective association was found between physical fitness and CAD than weight and CAD. 

How Does This Affect You?

The WISE results suggest that physical inactivity may be a more powerful risk factor for heart disease than overweight and obesity. Although doctors should and will continue to recommend weight reduction in their overweight patients at risk for CAD, this study suggests that an even greater emphasis should be made on physical fitness in the fight against this disease among women.

While these findings are certainly useful, they also point out how risk factors for coronary heart disease, and all chronic disease for that matter, are complex and difficult to tease apart. In fact, another study published in the same issue of the Journal of the American Medical Association found that, in direct contrast to impact on heart disease, overweight and obesity were more predictive of diabetes, than the level of physical activity. And diabetes, of course, is one of the most important risk factors for CAD.