Coronary Heart Disease – Part II: Understanding Risk Factor Basics

Suggested Citation: Garko, M.G. (2012, October). Coronary heart disease – Part II: Understanding risk factors.  Health and Wellness Monthly. Retrieved (insert month, day, year), from www.letstalknutrition.com.

 

 

Coronary Heart Disease – Part II: Understanding Risk Factor Basics 

 

Michael Garko, Ph.D.

Host of Let’s Talk Nutrition

 

Introduction

“Life is not living, but living in health” (Marcus Valerius Martialis, 1st century Roman poet). Living in health is not automatically guaranteed. This is something most people understand in principle even if they do not engage in the day-to-day practice of maintaining their health, preventing disease and slowing down the aging process.

Living in health requires a considerable measure of initiative, information and insight. The grim morbidity and mortality statistics on coronary heart disease (CHD) reveal how challenging and elusive living in health can be (see Garko, 2012). In fact, since 1921 CHD has debilitated and killed more Americans than any other degenerative disease. Ironically, CHD is one of the most preventable degenerative diseases.

In the spirit of helping health consumers take personal responsibility for living in health and preventing CHD and its consequences (e.g., disability and death), the October, 2012, issue of Health and Wellness Monthly focuses on some of the basics of risk factors as they pertain to CHD. A brief history of risk factors for CHD will be presented. This will be followed by a discussion defining risk factors and describing some important aspects and issues surrounding them, generally, and their implication with CHD, specifically.

Beyond its immediate purpose, this month’s newsletter is intended also to serve as a foundation for upcoming issues of Health and Wellness Monthly in which major causes and risk factors responsible for the development of CHD will be discussed and specific health and nutrition strategies will be recommended to help prevent CHD.

 

History on CHD Risk Factors

The meaning of the concept of risk factors for CHD has evolved over several decades, as has the actual list of risk factors and causes responsible for CHD. During the 1930s and 1940s, public health officials realized that the United States was in the grips of a CHD epidemic that was killing millions of Americans at an increasingly alarming rate. Determined to abate the growing morbidity and mortality rate attributable to CHD, medical scientists theorized about the cause of CHD. Some favored the single-cause theory with dietary fat and cholesterol being the culprits for atherosclerosis, while others were inclined more toward a multiple-cause explanation for CHD.

Nevertheless, in 1948 the United States federal government in its determination to conquer CHD initiated the first large-scale public health study to uncover the causes of CHD. It was called the Framingham Heart Study and is still in progress today. Investigators enrolled 5,209 people into the study, all of whom lived in Framingham, Massachusetts, a suburb of Boston. Dr. William Kannel was the first director of the study. It was he who coined the phrase “cardiovascular risk factors” (see Black, 1993).

The Framingham Heart Study has made a major contribution in identifying those factors and causes which put people at risk for developing CHD. It has helped to spawn a major research effort in the United States with countless studies and public health initiatives designed to understand the pathogenesis of CHD and how to prevent it.

Defining and Describing Risk Factors

Risk factors can be defined as variables possessing the potential to increase the likelihood of developing a particular disease (e.g., coronary heart disease). They are linked to a disease by means of a statistical association or correlation. The stronger the statistical association is the stronger the inference that can be made about a particular factor putting people at risk for developing a disease such as CHD.

It is important to understand that while a particular risk factor or set of risk factors increases the likelihood of developing CHD, this does not mean that there is a certainty of acquiring the disease. At the same time, however, because an individual does not manifest any risk factor or set of risk factors does not mean that he/she does not have CHD or will not develop it. It is not uncommon for people to have heart attacks without manifesting any of the recognized risk factors for CHD (see Black, 1993).

Correlational vs. causal. A common misunderstanding is that all risk factors for CHD are causes of it. As it was pointed out, the relationship between risk factors and CHD is correlational in nature. Their connection to CHD is not causal in nature. Risk factors represent a necessary condition for the development of CHD. Causes of CHD represent a sufficient condition for CHD. In other words, a particular risk factor contributes to CHD, while a cause of CHD ensures it. For example, age and gender (i.e., being male) are recognized risk factors contributing to the development of CHD but they have not been established scientifically as causing CHD independent of any other factor.

Risk factors serve as the scientific basis for the causes of CHD and can become established causes of it. According to the U.S. Department of Health and Human Services – Centers for Disease Control and Prevention (2003), “major epidemiologic studies revealed that incidence rates (measures of the occurrence of new cases of CHD, whether fatal or not) could be predicted by blood cholesterol level, blood pressure level, smoking, diabetes, and certain other potentially modifiable characteristics. These characteristics, recognized as ‘risk factors’ since the 1960s, were ultimately established as the major causes of CHD” (p. 22). In order for a risk factor (e.g., smoking) to be recognized as a cause for CHD (or any disease for that matter), sufficient scientific evidence must exist to show that it increases the overall number of cases of CHD or makes the disease develop sooner than it otherwise would (U.S. Department of Health and Human Services, 2004).[1]

In sum, unless a risk factor has been established through rigorous scientific studies to bring about CHD independent of other factors, then it cannot be considered to be a cause of it. Risk factors for CHD put people at some level of statistical risk for developing it but they do not cause it. All recognized causes of CHD are risk factors but not all risk factors are causes of CHD.

Categories of risk factors. Typically, risk factors for CHD are placed into the two major categories of heredity and lifestyle. While convenient, this approach lacks a certain amount of precision. For example, obesity is put typically into the lifestyle category. However, being obese reflects an acquired condition, which results from the lifestyle behavior of eating a weight inducing diet or leading a sedentary life or both. Hence, a more exact approach would be to classify risk factors using the three categories of heredity, acquired conditions and lifestyle variables.

As these terms are used here, heredity refers to genetically determined physiological and psychological characteristics/traits, conditions or processes. In contrast to heredity, acquired conditions are physiological and psychological characteristics or processes which are not inherited and brought about by lifestyle. Lifestyle is a way of living that includes habits and behaviors, along with attitudes, values and beliefs.

Included in the category of heredity are risk factors such as gender, race and other inherited characteristics. Included in the category of acquired conditions are risk factors such as elevated blood pressure, elevated serum cholesterol, glucose intolerance, metabolic syndrome and left ventricular hypertrophy, among other characteristics. Included in lifestyle are risk factors such as excessive tobacco and alcohol use, unhealthy, atherosclerotic inducing diet, lack of exercise and physical activity, high stress levels and other factors related to day-to-day living.

Modifiable and non-modifiable risk factors and causes. In addition to categorizing risk factors and causes in terms of heredity, acquired conditions and lifestyle, they can be further classified as being modifiable and non-modifiable, a frequently used approach. Non-modifiable risk factors are genetically determined traits (e.g., age, gender & race-ethnicity). Modifiable risk factors involve lifestyle variables (e.g., excessive alcohol & tobacco use, high stress levels, lack of exercise & physical activity, poor nutrition, etc.) and acquired conditions (e.g., elevated blood pressure, overweight-obesity, insulin resistance, etc.). Lifestyle and acquired conditions are assumed in the literature to be changeable and ideally subject to improvement and prevention, while heredity based factors are viewed as fixed and unchangeable.

Making the list. Although they are not causal in nature, risk factors play a profound role in the development of CHD. Consequently, they should not be taken lightly. Yet, they should not be put on the list of recognized risk factors for CHD until they have met certain criteria. Black (1993) has identified a set of six criteria for a variable to be considered a legitimate and meaningful risk factor.

First, the statistical association between the risk factor and CHD must be strong. That is, according to Black (1993), “the presence of the factor should at least double the risk of disease” (p.25).

Second, the statistical association should be consistent in that the “risk factor should produce disease regardless of gender, age, or race and the association should be present in all or most of the studies in which it has been evaluated (Black, 1993,  p. 25).

Third, the statistical relationship between the risk factor and CHD must make biological sense. Black (1993) contends that “unless such a relationship is biologically plausible, the statistical association may have little meaning” (p. 25). It is often the case in science that statistically significant findings are of no real practical importance.

Fourth, the health impact of risk factors should be able to be demonstrated experimentally in a laboratory. Black (1993) admits that this criterion is difficult to satisfy, especially since it is not always feasible or ethical to subject humans to experiments.

Fifth, treatment that can favorably modify the impact of the risk factor should reduce the incidence of the disease. Black (1993 recognizes that this particular criterion has been satisfied for some but not all of the recognized risk factors.

Lastly, the risk factor must make an independent contribution to increasing the likelihood of developing the disease.[2] Again, Black (1993) admits that some proposed risk factors simply occur together with other more legitimate risk factors for CHD.

Multi-factorial and interactional. Similar to other degenerative diseases, CHD is not associated with or caused by a single variable. Rather, CHD is multi-factorial. The research on CHD provides convincing evidence that it stems from a complex of interacting traits, acquired conditions and lifestyle variables that implicate various environmental, behavioral, psychological, physiological, social and genetic factors.

Some risk factors are described in the literature as being an independent (e.g., smoking) because they have the potential to bring about CHD single-handedly. However, risk factors and causes can and most often interact and work together with one another to create a greater likelihood of developing CHD and produce a greater deleterious impact on a person’s cardiovascular health.[3] The interactional nature of risk factors is reflected in the following statement in a report by the Centers for Disease Control and Prevention (1984):

Cigarette smoking increases the risk of developing CHD, and this effect is independent of the other major risk factors for CHD. However, smoking interacts with the other major risk factors (elevated serum cholesterol and hypertension) to substantially increase the CHD risk beyond the sum of the independent components (Figure 1). Each factor contributes about the same order of magnitude of risk for CHD. When one factor is present, the risk approximately doubles; with two factors, the risk is fourfold greater; and when all three are present, the CHD risk is eightfold greater than when none of the three factors are present (pp. 677-678).

More are worse. It stands to reason that the more risk factors and causes an individual possesses for CHD the greater the chances of that person developing and dying from the disease. Unfortunately but not surprisingly, the Centers for Disease Control and Prevention (2005) reported that “a substantial portion of the population has multiple risk factors, increasing their likelihood of cardiovascular disease” (p.113). For example, in analyzing data from the 2003 Behavioral Risk Factor Surveillance System (BRFSS) survey the CDC found that almost 26% of the respondents reported having all six of the following risk factors: High blood pressure, high blood cholesterol, diabetes, obesity, physically inactive and smoking. Thirty seven percent of the respondents in the survey reported having two or more of these risk factors. 

Modifying risk factors. With respect to modifying risk factors, Black (1993) points out that undergoing treatment to reduce the deleterious effect of a risk factor does not automatically translate into risk reduction or that taking action to modify a risk factor does not guarantee that the probability of a heart attack or stroke will be eliminated. Fortunately, many of the modifiable risk factors for CHD can be tackled through prevention, early detection and treatment (Centers for Disease Control and Prevention, 2005). The Centers for Disease Control and Prevention (2005) reported that modifiable risk factors such as high blood pressure, high cholesterol, diabetes, tobacco use, and obesity and lack of exercise are its main targets for primary and secondary prevention for CHD. So too should they be the targets in every individual’s quest to live in health and avoid CHD.

Conclusion

Perhaps Marcus Valerius Martialis’ quote about living in health should be modified to read, “Life is not living, but living in health by taking personal responsibility.”  If CHD is to be prevented, then health consumers need to assume responsibility in maintaining their cardiovascular health. One step in that direction is to learn about risk factor basics for CHD. Having this kind of knowledge can assist in (1) assessing (with the help of a healthcare professional) the likelihood of developing CHD and (2) eliminating or at least reducing the impact of specific risk factors such as high blood pressure, high blood cholesterol, diabetes, obesity, physical inactivity and smoking. Prevention begins with health consumers knowing about the nature of those factors that create the risk of developing CHD.

In upcoming issues in the series on cardiovascular health being featured in Health and Wellness Monthly, readers will learn specific details about modifiable and non-modifiable factors putting people at risk for CHD. Knowing about the various causes and risk factors for CHD can help health consumers modify their lifestyle to prevent CHD.

References

Black, W.K. (1992). Cardiovascular risk factors. In B. L. Zaret, M. M. Moser & L. S. Cohen (Eds.), Yale university school of medicine heart book (pp. 23-35). New York: Hearst Press.

Centers for Disease Control and Prevention (1984). Perspectives in disease prevention and health promotion smoking and cardiovascular disease. (Mortality and Morbidity Weekly Report, 32(52), pp. 677-679). Atlanta, GA: Centers for Disease Control and Prevention.

Garko, M.G. (2012, September). Coronary heart disease – Part I: The prevalence, incidence, mortality and pathogenesis of the leading cause of death in the United States. Health and Wellness Monthly. Retrieved September 5, 2012, from www.letstalknutrition.com.

 

Kraemer, H.C., Stice, E., Kazdin, A. & Offord, D. (2001). How do risk factors work together? Mediators, moderators, and independent, overlapping, and proxy risk factors. American Journal of Psychiatry, 158, 848-856.

U.S. Department of Health and Human Services (2003). A public health action plan to prevent heart disease and stroke. Washington, DC: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention

U.S. Department of Health and Human Services (2004). The health consequences of smoking: A report of the Surgeon General. Washington, DC: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health.

 

Suggested Citation: Garko, M.G. (2012, October). Coronary heart disease – Part II: Understanding risk factors.  Health and Wellness Monthly. Retrieved (insert month, day, year), from www.letstalknutrition.com.

 

 

 

 

 



[1] The Surgeon General created criteria to conclude that a risk factor (e.g., smoking) causes a particular disease such as coronary heart disease. Although the criteria have been used to establish smoking as a proven cause for diseases (e.g., CHD), scientists can and do apply them when seeking to establish that other risk factors (e.g., diabetes, elevated blood pressure, elevated serum cholesterol) have not just an association or correlational relationship with CHD but rather a causal relationship to it. For a listing and description of the criteria, the reader can refer to The Health Consequences of Smoking: A Report of the Surgeon General (U.S. Department of Health and Human Services, 2004).

 

[2]Black is not using the term “independent” to imply that risk factors are causal in nature as it was discussed earlier in the newsletter.

 

[3] The reader can refer to Kraemer et al. (2001) for an in-depth, cogent discussion on the different ways in which risk factors can interact with one another.