Oslo Study (Cohort)

Background/Question:

The study was a combined investigation of the epidemiology of coronary heart disease in young and middle-aged Oslo men and the effectiveness of preventive interventions in those who were at risk for developing coronary heart disease. The investigators sought to elucidate “the cause and effect mechanisms and development of means to control them to provide specific tools which may be applied to healthy high-risk individuals.” [1] While the Oslo cohort has been used as a population for dietary, smoking cessation and drug trials, this abstract will focus solely on the observational portion of the study.

Methods:

The survey examinations began in May 1972 and continued until December 1973. A questionnaire and invitation to participate was mailed to all Oslo men aged 40-49 and a random sample (7%) of men aged 20-39. The preliminary exam included “a nonfasting blood sample for total cholesterol, triglycerides and glucose, measuring of height, weight, blood pressure […] and a miniature chest x-ray.” A total of 17,965 men was examined. Based on results of the baseline examination, risk scores were calculated for each man using cholesterol, systolic blood pressure and number of cigarettes smoked per day, using a method similar to that employed by Westlund and Nicolaysen in a prior Oslo cholesterol study. [1] The risk score was an early attempt to look at multifactorial risk by comparing combined findings between diseased and disease-free subjects in the cohort [2] Subsequent studies developed multivariate analyses from follow-up data in the cohort. [1]

Results:

The group of men with known myocardial infarction and angina pectoris had higher values of all risk factors (cholesterol, triglycerides, blood glucose, systolic and diastolic blood pressure and total risk score) than men without coronary heart disease. Across strata of age, total risk score based on a combination of risk factors increased from age 35-39 to age 45-49. [1] High levels of physical activity were associated with lower serum cholesterol levels. Heavy cigarette smoking was also associated with high serum cholesterol level (257.9 mg/mL for 0-5 years of smoking versus 273.7 for 25+ years of smoking for 40-49 year old men).

After 21 years of follow-up, “the cohort had a lower mortality rate than the general Norwegian population. First nonfatal and fatal MIs declined in each age and birth cohort during the entire follow-up.” [2] Several papers were published on risk factors for stroke in the cohort (blood glucose, cholesterol and blood pressure). [3-5]

Conclusions/Discussion:

The baseline survey portion of the study ascertained factors positively associated with coronary heart disease in one of the earliest systematic attempts to identify risk factors for CVD, thus establishing personal and population needs for interventions to decrease risk. The investigators had concerns about the limitations of a cross-sectional computation of risk in a case-control design: “The risk score is based on mutual independence of the actual risk variables, which the present study has proved not always to be the case. This may weaken the validity of the risk score tables.” [1] Strengths of the study include its early focus on risk factors, a thorough baseline examination, sample size, and availability of the subjects for follow-up studies and trials in the Norwegian population.