Paris Prospective Study

Background/Question:

The Paris Prospective Study examined coronary heart disease incidence (CHD) in France, with an interest in explaining the “strikingly lower” French mortality rates compared to other developed countries. [1] Middle aged police officers were enrolled to achieve a “total occupation-based French population.” [1] While the study was created to assess the peculiarities of risk among the French cohort, the data were also used to compare incidence rates among other developed countries and to explain the “French Paradox” of lower CHD incidence.

Population and Methods:

The study involved 7453 native Frenchmen, aged 42-53 years, employed by the Paris Police Administration. Of 8297 subjects originally recruited, 7990 underwent the initial examination (96.3% response rate). The subjects completed a baseline examination between the years of 1967 and 1972 that included an ECG, blood and urine samples for cholesterol and glucose measures, systolic and diastolic blood pressure measurements and interviews on demographic factors and medical history, family history of illness, prior cardiovascular disease, diabetes and smoking status. Of these participants, 245 were found to be born outside France, 105 had pre-existing heart conditions, and 187 were later lost to follow-up. Of the original cohort, 4.7% of subjects were lost to follow-up over a 20 year period. [2]

Results:

Follow-up data were taken at intervals, the earliest as of January 1, 1975, when 150 incident cases of CHD had occurred. The calculated mean incidence rate in this follow-up was 5.1/1,000. [2] The investigators hypothesized that risk was related to cholesterol and blood pressure levels, cigarette smoking, diabetic status and ECG abnormalities. [2] Analyses found that individuals with a greater number and severity of risk factors were more likely to develop CHD. [2]

The study demonstrated graded and independent relative risk of coronary events according to arbitrary cut points for CVD risk factors, on the order of 3-4 fold for each of cholesterol and blood pressure and diabetes, 2 fold for smoking, 6 fold for LVH on ECG, 10 fold for pressure and cholesterol combined, and 7 fold for a multifactorial risk score. Overall 4-year CHD mortality was 5 per 1000 which they indicate was about half of that from U.S. studies of the time.

Subsequent studies found blood glucose, body fat, and ECG abnormalities significant independent predictors of CHD incidence and mortality. An analysis of risk for sudden death dealt with 118 events at 23 years follow-up and found the aforementioned risk factors contributed to incidence of sudden cardiac death. [3] A later study showed decreased survival rates across 2 hour blood glucose fractiles with risks greater that those in the Whitehall and Helsinki Policemen cohorts.[4]

Conclusions/Discussion:

This 1977 report confirmed a lower attack rate among this French cohort compared to the U.S. and was early to call attention to the low risk portion of the population, in which the lower 6 % in combined risk score remained entirely attack-free. It was also early to propose possible influences on the lower rate in France, including lesser duration of exposure due to the privations of World War II. It was also early to point out the need for a comprehensive and strategic health policy of prevention beginning with diet and tobacco education among youth. The results of the Paris Prospective Study confirmed findings in other studies. Risk factors such as high blood pressure and cholesterol, diabetes, cigarette smoking and ECG abnormalities are associated with CHD incidence. The study was able to “establish incidence of CHD in an occupational group of Frenchmen between the ages of 40 and 60” that allowed comparisons of risk factors in the cohort and generalizations to the French and their culture.

The study was also useful in investigating what came to be known as “the French paradox.” As Ducimetiere points out, “…it was realized that French death-certification habits might explain, at least in part, the apparently very low mortality rates from CHD. In a more detailed analysis of mortality statistics by cause, combinations of subcodes of the International Classification of Diseases dispersed under different headings gave much more reasonable estimates of the burden of CHD on French mortality.” [1] Ultimately, the strengths of the Paris Prospective Study lie in the well-defined population, high response rates, variety and quality of risk measurements, effective long-term follow-up and analysis in a unique French population. Limitations include the exclusively male population and the fact that anoccupational sample cannot be considered representative of the country. The French Paradox was not confirmed in the subsequent MONICA surveys of three regions in France. (HB)