Levels of Risk Factors Associated with Heart Attacks

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The summary below is from the full report titled "Relative Importance of Borderline and Elevated Levels of Coronary Heart Disease Risk Factors." It is in the 15 March 2005 issue of Annals of Internal Medicine (volume 142, pages 393-402). The authors are R.S. Vasan, L.M. Sullivan, P.W.F. Wilson, C.T. Sempos, J. Sundström, W.B. Kannel, D. Levy, and R.B. D'Agostino.

What is the problem and what is known about it so far?

In the United States, coronary heart disease (CHD) is the most common cause of death and disability in middle-aged and older men and women. Coronary heart disease blocks the flow of blood through the arteries of the heart. If a blockage lasts long enough, a heart attack occurs and parts of the heart muscle die. There are many risk factors for developing CHD, including older age, high blood pressure, diabetes, smoking, high levels of total and low-density lipoprotein ("bad") cholesterol, low levels of high-density lipoprotein ("good") cholesterol, and a family history of a parent or sibling having CHD at an early age. Many studies show that most heart attacks occur in people with elevated risk factors. However, few studies have assessed whether borderline levels of risk factors account for many heart attacks.

Why did the researchers do this particular study?

To describe numbers of adults who have different levels of CHD risk factors and to see how often heart attacks occur in those with borderline rather than high levels of risk factors.

Who was studied?

White non-Hispanic men and women in the United States. All were between the ages of 35 and 74 years, and none were known to have CHD.

How was the study done?

First, the researchers used data from a large ongoing study in Framingham, Massachusetts, to find the 10-year rates of CHD events among white adults with different levels of 5 risk factors. They defined CHD events as heart attacks or death from CHD. They categorized each adult's blood pressure, low-density lipoprotein cholesterol level, high-density lipoprotein cholesterol level, glucose level, and smoking status as optimal (normal or absent), borderline (suboptimal but not clearly abnormal), or high (clearly abnormal). Second, the researchers used data from a national survey and the 2000 U.S. Census to find numbers of white non-Hispanic adults in the United States with the various levels of the 5 risk factors. Third, the researchers applied the CHD event rates from the Framingham Study to the survey data so that they could estimate the fractions of CHD events in white non-Hispanic persons in the United States arising from the different levels of risk factors.

What did the researchers find?

About 60% of the men and 50% of the white non-Hispanic women in the United States had high levels of 1 or 2 risk factors. About 25% of the men and 40% of the women in the national survey sample had borderline levels of 1 or more risk factors but no elevated ones. Very few persons had optimal levels or no risk factors. More than 90% of the CHD events over a 10-year period occurred in those with high levels of 1 or more risk factors. Nearly one sixth of the events in men occurred before age 55 years. Fewer than 10% of the events occurred in adults with only borderline levels of risk factors (without a single elevated one). Very few events occurred in those without risk factors.

What were the limitations of the study?

The research involved only white non-Hispanic men and women. Some risk factors, such as obesity and inactive lifestyle, were not studied.

What are the implications of the study?

Most middle-aged and older white non-Hispanic adults in the United States have high levels of 1 or more risk factors for CHD. Borderline levels of risk factors are also common, but borderline levels alone without elevated levels probably account for only a small proportion of CHD events over a 10-year follow-up period.