The Cooper Institute
 

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH

 
 
 

Decreasing the Risk of Cardiovascular Death: How Low Can You Go?

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Monday, Jan 14, 2013

Although cardiovascular disease (CVD) has been the leading cause of death in the U.S. for over a century, risk factors for CVD were completely unknown as recently as the 1950’s. In fact, heart attack and stroke were thought to be simply a natural consequence of the aging process up until that time! In the late 1940’s, Dr. William Kannel boldly suggested that CVD might be related to behaviors or environmental factors. Accordingly,  the epic Framingham Heart Study was launched in 1948. Residents of Framingham MA were invited to participate in a lifelong research project where they would receive free comprehensive medical exams every two years for the rest of their life. In exchange for these free exams, subjects agreed to have their data included in a large data base, and to be tracked for morbidity (illness) and mortality (death). As the data began to pile up, scientists noticed that people with certain behaviors and characteristics were more likely to die from heart attacks and strokes than people without those same behaviors and characteristics. Today we call these variables ‘risk factors’. They include such things as abnormal blood cholesterol level, hypertension, tobacco use, obesity, etc. By 1998, the Framingham Risk Score (FRS)1 had been developed; FRS estimates an individual’s 10-year risk for a future coronary event based on their current risk factors. If the 10-year risk is less than 10%, then the individual is deemed ‘Low Risk’. The Low Risk group comprises a substantial proportion of U.S. adults; with more than 100 million individuals categorized as such.

Over the past 40 years, researchers at The Cooper Institute have shown repeatedly that cardiorespiratory fitness level (CRF) is a powerful risk factor for CVD and other types of morbidity and mortality. Because CRF is not part of the Framingham Risk Score, Cooper researchers wanted to determine whether or not a Low Risk individual’s CRF level added to the predictive value of the FRS. Accordingly, 11,190 Low Risk men and women with an average age of 41 years underwent a maximal treadmill stress test during their Cooper Clinic exam to determine their CRF level. Subjects were categorized as being low fit if they scored in the bottom 20% compared to others of their same age group and gender. Subjects scoring in the next 40% were categorized as being moderately fit, while those scoring in the top 40% were categorized as being high fit. The subjects were followed for an average period of 27 years; 214 of them died from CVD during this time.  The CVD death rate across CRF categories is shown in the Figure below. Compared to low fit subjects, men and women who were moderately fit were about 30% less likely to die from CVD. High fit men and women were about 65% less likely to die from CVD than those who were low fit2.

Remember that while all of these men and women were categorized as Low Risk based on the FRS at the time of their exam, the FRS does not take CRF into account. So, the take home message is that while it’s very important to control traditional risk factors like blood pressure, cholesterol, weight, and tobacco use, it’s not enough to get your CVD risk as low as it can be. Individuals must also achieve a moderate, or preferably a high level of CRF in order to minimize risk as much as possible. Achieving a moderate level of CRF is well within the reach of most adults who meet the public health guidelines for physical activity (accumulate 150 minutes or more of moderate intensity aerobic activity each week). In order to reach a high level of CRF, it’s likely that individuals will need to include some vigorous intensity aerobic activity as well.

So, the next time your internist or cardiologist gives you a physical exam, be sure to ask for your Framingham Risk Score. Keep in mind that even if your doctor tells you that you are in the Low Risk category, you can further decrease your risk by achieving a moderate or high level of cardiorespiratory fitness.

References   

1. Wilson, PW et al. Prediction of coronary heart disease using risk factor categories. Circulation. 1998;97:1837-1847.

2. Barlow, CE et al. Cardiorespiratory fitness and long-term survival in ‘low risk’ adults. J. Am. Heart Assoc. 2012:1:e001354 doi.