In this study, we calculated the lifetime risk of cardiovascular disease according to age, sex, race, and other risk factors across multiple birth cohorts. There were several important findings. First, our data strongly reinforce the influence of traditional risk factors on the lifetime risk of cardiovascular disease. Even a relatively low burden of these risk factors was associated with significant increases in the long-term risk of cardiovascular disease, and the absence of traditional risk factors was associated with a very low lifetime risk. Second, despite the development of notable secular trends in the prevalence of risk factors during the past 40 years, we observed that the effect of these factors, when present, remained remarkably consistent across birth cohorts. In addition, although the prevalence of risk factors overall was higher among blacks than among whites, the lifetime risks of end points related to cardiovascular disease were similar among blacks and whites when their risk-factor profiles were similar.
The presence or absence of traditional risk factors appears to represent a much more consistent determinant of the long-term risk of cardiovascular disease than race or birth cohort. For example, among 55-year-old men with two or more major risk factors, the 20-year adjusted risk of death from cardiovascular disease was only 4% lower among men born in or after 1920 than it was among those born before 1920 (16.8% vs. 20.7%), presumably reflecting the potential influences of subsequent treatment. In contrast with these modest effects related to birth cohort, the 20-year adjusted risk of death from cardiovascular disease was substantially greater across risk-factor strata. For example, among men born before 1920, those with only one risk factor had a 20-year adjusted risk of death from cardiovascular disease that was 13 percentage points lower than that among men with two or more major risk factors (7.5% vs. 20.7%). Thus, in the younger birth cohorts, the marked decrease in the proportion of cohort members who were classified in the highest risk group (persons with two or more major risk factors) appears to account for the majority of the decline in cardiovascular events.
We believe these findings have important implications for clinical disease prevention and public health practice. First, the effect of untreated risk factors has been fairly constant for decades. Therefore, the present estimates of lifetime risk, made on the basis of current or projected risk-factor levels, may be important in estimating the future burden of cardiovascular disease in the general population. Second, efforts to lower the burden of cardiovascular disease will require prevention of the development of risk factors (primordial prevention) rather than the sole reliance on the treatment of existing risk factors (primary prevention).
Our data are also consistent with earlier observations suggesting that the decline in cardiovascular event rates in the general population reflects changes in the prevalence of risk factors rather than the effects of treatment alone.10,35
For example, 44.3% of the overall decline in U.S. rates of death from coronary heart disease in 1980 and in 2000 was attributed to population changes in levels of serum total cholesterol (24.2%) and systolic blood pressure (20.1%). The effects of clinical treatment on these risk factors were more modest, with statin and antihypertensive therapy accounting for 4.9% and 7.0% of the decline, respectively.10,35
We extend these observations to long-term risk estimates, showing that changes in the prevalence of risk-factor profiles strongly influence estimates of lifetime risk in the general population.
Prior studies have consistently shown that a higher burden of risk factors, measured individually or in aggregate, is associated with a markedly higher lifetime risk of cardiovascular disease.7,36,37
However, the majority of these earlier, smaller studies were confined to single cohorts with predominantly white participants. We believe that our analysis, which is based on pooled data from multiple birth cohorts, with both black participants and white participants and varied geographic origin, provides more representative estimates of the lifetime risks of cardiovascular disease.
Investigators in earlier studies, using standard methods, have observed that blacks and whites had similar magnitudes of relative risks for cardiovascular disease events associated with individual risk factors.38–41
Thus, the higher prevalence of adverse risk factors among blacks translates into a higher observed risk of cardiovascular disease. In the present study, we also observed a higher prevalence of risk factors among blacks than among whites. However, because of the higher burden of competing risks among blacks, which our analytical approach accounted for, we observed similar lifetime risks of death from cardiovascular disease among blacks and whites, despite the higher burden of risk factors among blacks.
There are several limitations of the present study. First, our algorithm for aggregate risk-factor stratification included treated patients in the highest-risk groups. Although the inclusion of treated patients may have resulted in some misclassification, these participants represent a very small percentage of the overall cohort. The effect of this categorization, if anything, tends to underestimate future risk in the strata with the highest risk-factor burden. Furthermore, we have validated this algorithm in multiple and diverse cohorts, including the Framingham Heart Study,7
the Chicago Heart Association Detection Project in Industry,36
the Coronary Artery Risk Development in Young Adults (CARDIA) study,2
the Multi-Ethnic Study of Atherosclerosis (MESA),2
and the Dallas Heart Study,42
using diverse clinical and subclinical end points. We have also observed that the association between risk-factor categories and risk of cardiovascular disease does not depend on the presence or absence of any one risk factor alone. Therefore, we believe that our classification of risk-factor burden provides a reliable, and conservative, projection of the risk of cardiovascular disease.
Second, we were not able to estimate lifetime risks of death from cardiovascular disease for persons with risk factors measured in the most recent decade included in the study because the estimation of lifetime risk ideally requires several decades of actual follow-up from the point at which the risk factor is measured. Nevertheless, because of the consistency of results across birth cohorts in which the prevalence of elevated risk factors varies, we believe that the present data are applicable to contemporary cohorts.
In summary, the Cardiovascular Lifetime Risk Pooling Project represents a combined analysis of data from more than 250,000 participants derived from 18 cohorts during a period of more than 50 years. We found that the presence of elevated levels of risk factors at all ages translated into markedly higher lifetime risks of cardiovascular disease across the lifespan. These findings were consistent across risk-factor strata among both blacks and whites and across multiple birth cohorts.