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 or equal to120/80 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 72,144 men aged 35 through 39 years and
270,671 men aged 40 through 57 years screened (1973-1975) for the Multiple
Risk Factor Intervention Trial (MRFIT); in Chicago, a total of 10,025 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 = 366,559).
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.