MRFIT study

The Multiple Risk Factor Intervention Trial (MRFIT) was one of the coronary heart disease prevention trials recommended to the National Heart and Lung Institute in 1971 as an alternative to a national single-factor dietary trial, which was judged to be infeasible

• the study was designed to assess the combined influence of blood pressure (BP), serum cholesterol level, and cigarette smoking on death from coronary heart disease (CHD) and to describe how these associations vary with age, data on those factors and on mortality for 316,099 men screened for the Multiple Risk Factor Intervention Trial (MRFIT) were examined
• vital status of participants has been determined after an average follow-up of 12 years; 6327 deaths from CHD have been identified
• strong graded relationships between serum cholesterol levels above 4.65 mmol/L (180 mg/dL), systolic BP above 110 mm Hg, and diastolic BP above 70 mm Hg and mortality due to CHD were evident. Smokers with serum cholesterol and systolic BP levels in the highest quintiles had CHD death rates that were approximately 20 times greater than nonsmoking men with systolic BP and cholesterol levels in the lowest quintile.
• Systolic and diastolic BP, serum cholesterol level, and cigarettes per day were significant predictors of death due to CHD in all age groups. Systolic BP was a stronger predictor than diastolic BP
• for each five-year age group, the relationship between serum cholesterol and CHD death rate was continuous, graded, and strong.
  • for the entire group aged 35 to 57 years (men) at entry, the age-adjusted risks of CHD death in cholesterol quintiles 2 through 5 ([4.71 to 5.22, 5.25 to 5.69, 5.72 to 6.31, and greater than or equal to 6.34 mmol/L) relative to the lowest quintile were 1.29, 1.73, 2.21, and 3.42.
  • of all CHD deaths, 46% were estimated to be excess deaths attributable to serum cholesterol levels greater than or equal to 4.65 mmol/L, with almost half the excess deaths in serum cholesterol quintiles 2 through 4
  • the pattern of a continuous, graded, strong relationship between serum cholesterol and six-year age-adjusted CHD death rate prevailed for nonhypertensive nonsmokers, nonhypertensive smokers, hypertensive nonsmokers, and hypertensive smokers. These data of high precision show that the relationship between serum cholesterol and CHD is not a threshold one, with increased risk confined to the two highest quintiles, but rather is a continuously graded one that powerfully affects risk for the great majority of middle-aged American men

The MRFIT study, and other similar studies, were able to show a continuous relationship between risk of coronary artery disease and cholesterol down to at least 3.0 mmol per litre and perhaps further. It was also able to show that therapy is perhaps more important in higher risk groups, for example diabetics.

For ten years of reduction there was about a 30% reduction in the disease levels.

Further at:

• 4 years: 13% improvement in primary prevention 17% improvement in secondary prevention
• 2 years: fatalities reduced by 7% for a 10% cholesterol reduction

Reference:

1. Arch Intern Med 1992 Jan;152(1):56-64
2. JAMA 1986 Nov 28;256(20):2823-8