Context: Three major coronary risk factors-serum cholesterol level, blood pressure, and smoking-increase incidence of coronary heart disease (CHD) and related end points. In previous investigations, risks for low-risk reference groups were estimated statistically because samples contained too few such people to measure risk.
Objective: To measure long-term mortality rates for individuals with favorable levels for all 3 major risk factors, compared with others.
Design: Two prospective studies, involving 5 cohorts based on age and sex, that enrolled persons with a range of risk factors. Low risk was defined as serum cholesterol level less than 5.17 mmol/L (<200 mg/dL), blood pressure less than orequal to 120/80 mm Hg, and no current cigarette smoking. All persons with a history of diabetes, myocardial infarction (MI), or, in 3 of 5 cohorts, electrocardiogram (ECG) abnormalities, were excluded.
Setting and participants: In 18 US cities, a total of 72144 men aged 35 through 39 years and 270671 men aged 40 through 57 years screened (1973-1975) for the Multiple Risk Factor Intervention Trial (MRFIT); in Chicago, a total of 10025 men aged 18 through 39 years, 7490 men aged 40 through 59 years, and 6229 women aged 40 through 59 years screened (1967-1973) for the Chicago Heart Association Detection Project in Industry (CHA) (N = 366559).
Main outcome measures: Cause-specific mortality during 16 (MRFIT) and 22 (CHA) years, relative risks (RRs) of death, and estimated greater life expectancy, comparing low-risk subcohorts vs others by age strata.
Results: Low-risk persons comprised only 4.8% to 9.9% of the cohorts. All 5 low-risk groups experienced significantly and markedly lower CHD and cardiovascular disease death rates than those who had elevated cholesterol level, or blood pressure, or smoked. For example, age-adjusted RRs of CHD mortality ranged from 0.08 for CHA men aged 18 to 39 years to 0.23 for CHA men aged 40 through 59 years. The age-adjusted relative risks (RRs) for all cardiovascular disease mortality ranged from 0.15 for MRFIT men aged 35 through 39 years to 0.28 for CHA men aged 40 through 59 years. The age-adjusted RR for all-cause mortality rate ranged from 0.42 for CHA men aged 40 through 59 years to 0.60 for CHA women aged 40 through 59 years. Estimated greater life expectancy for low-risk groups ranged from 5.8 years for CHA women aged 40 through 59 years to 9.5 years for CHA men aged 18 through 39 years.
Conclusions: Based on these very large cohort studies, for individuals with favorable levels of cholesterol and blood pressure who do not smoke and do not have diabetes, MI, or ECG abnormalities, long-term mortality is much lower and longevity is much greater. A substantial increase in the proportion of the population at lifetime low risk could contribute decisively to ending the CHD epidemic.