Coronary heart disease (CHD) is usually associated with one or more characteristics known as risk factors. A risk factor is “an aspect of personal behavior or lifestyle, an environmental exposure or an inborn or inherited characteristic, which on the basis of epidemiologic evidence is known to be associated with” the occurrence of disease.
Several aspects of the association between a potential risk factor and the disease are evaluated before an association is considered causal. These include the strength or magnitude of the association, the consistency or repeatability of the association, temporality (the cause precedes the disease), dose response (greater dose leads to greater likelihood of disease), the biologic and epidemiologic plausibility of the association, coherence of the potential cause with what is known about the disease, a decrease in the incidence of disease when the potential cause is eliminated, and experimental evidence. Although few potential risk factors meet all of these criteria, the goal of epidemiologic investigations is to establish these characteristics.
The results of epidemiologic studies of disease etiology are frequently presented either as disease rates or as a relative risk. Relative risk is the rate of disease in a group exposed to a potential risk factor, divided by the rate of disease in an otherwise similar group that is unexposed to the risk factor. For example, if the rate of fatal myocardial infarction (MI) in a group of smokers was 120/100,000 per year, and the rate in comparable nonsmokers was 60/100,000 per year, the relative risk associated with smoking would be:
Relative risk = rate in exposed / rate in unexposed = (120/[100,000/yr])/(60/[100,000/yr]) = 2.0
The risk of MI is thus doubled in the smokers, or a 200% increase in risk compared with nonsmokers. A relative risk of 1.30 represents a 30% increase in risk; a relative risk of 3.0 represents a 300% increase, or a tripling of risk.
Several aspects of the association between a potential risk factor and the disease are evaluated before an association is considered causal. These include the strength or magnitude of the association, the consistency or repeatability of the association, temporality (the cause precedes the disease), dose response (greater dose leads to greater likelihood of disease), the biologic and epidemiologic plausibility of the association, coherence of the potential cause with what is known about the disease, a decrease in the incidence of disease when the potential cause is eliminated, and experimental evidence. Although few potential risk factors meet all of these criteria, the goal of epidemiologic investigations is to establish these characteristics.
The results of epidemiologic studies of disease etiology are frequently presented either as disease rates or as a relative risk. Relative risk is the rate of disease in a group exposed to a potential risk factor, divided by the rate of disease in an otherwise similar group that is unexposed to the risk factor. For example, if the rate of fatal myocardial infarction (MI) in a group of smokers was 120/100,000 per year, and the rate in comparable nonsmokers was 60/100,000 per year, the relative risk associated with smoking would be:
Relative risk = rate in exposed / rate in unexposed = (120/[100,000/yr])/(60/[100,000/yr]) = 2.0
The risk of MI is thus doubled in the smokers, or a 200% increase in risk compared with nonsmokers. A relative risk of 1.30 represents a 30% increase in risk; a relative risk of 3.0 represents a 300% increase, or a tripling of risk.
United States death rates in 1994 to 1995 from all cardiovascular diseases combined, acute MI, cancer, and other causes, for African-American and white women and men are presented in Chart given above
Cardiovascular disease continues to be the leading cause of death for African-American and white men and women throughout their life spans. Death rates from MI increase with age in men and women, with rates for women lagging 5 to 10 years behind those for men. The rate of acute MI is higher in African-American women than white women throughout their life span, whereas MI rates in white and African-American men are similar until age 65 years, when the rate in white men exceeds that in African-American men. In the Third National Health and Nutrition Examination Survey (NHANES III), the prevalence of a personal history of MI was higher for men than women among whites and Mexican Americans, but this difference was less pronounced among African Americans .
Coronary heart disease mortality rates have declined steadily since the late 1960s. From 1968 to 1984, CHD mortality declined at an average rate of 2% to 3% per year in all age groups, in both sexes, and in blacks and whites. From 1979 to 1985, the average annual percentage change in CHD mortality, for people aged 35 to 74 years, was –2.59% for white women, –3.37% for white men, –2.0% for African-American women, and –2.84% for African-American men. From 1987 to 1994, the average annual percentage change in CHD mortality, for people aged 35 to 74 years, was –4.5% for white women, –4.7% for white men, –4.1% for African-American women, and –2.5% for African-American men. There is ongoing speculation as to the cause of this decline in CHD mortality, although multiple causes are likely. Small, population-wide behavior changes leading to lower serum cholesterol, lower smoking rates, and lower blood pressure may account for as much as 50% of the decrease. Decreases in case fatality rates also have been documented. This indicates that changes in patient management, including more rapid access to emergency care and interventions that reduce infarct size and prevent death due to arrhythmias, may account for some of the decline in CHD mortality
Cardiovascular disease risk factors have additive effects. The MI risk in a person with three major risk factors is higher than that of a person with two or one . Furthermore, for any given combination of risk factors, at a given age, the risk is lower in women than men
The major known risk factors for cardiovascular disease wiil be reviewed in the following posts.
