Twenty-five-year prediction of stroke deaths in the seven countries study: the role of blood pressure and its changes.

BACKGROUND AND PURPOSE

This report explores the prediction of long-term stroke mortality in cohorts of the Seven Countries Study.

METHODS

Sixteen cohorts of men aged 40 to 59 years at entry were examined at years 0, 5, and 10, with mortality follow-up through 25 years.

RESULTS

Stroke death rates in 25 years were high in rural Serbia, Croatia, and Japan; intermediate in Italy, Greece, and urban Serbia; and low in Finland, the Netherlands, and the United States. Age and blood pressure were powerful predictors of 25-year stroke mortality in almost all cohorts and countries. Proportional hazards regression coefficients were .0232 increase in stroke death hazard per millimeter of mercury (t=14.60) for systolic blood pressure and .0409 (t=13.41) for diastolic blood pressure. Moderate blood pressure increases from low usual levels were associated with lower stroke mortality rates in years 10 to 25. Increases of blood pressure starting from high usual levels were associated with increased rates of stroke mortality. Systolic blood pressure was associated with stroke mortality at given levels of diastolic pressure, but diastolic blood pressure was not predictive of stroke mortality at given levels of systolic blood pressure.

CONCLUSIONS

Associations of systolic and diastolic blood pressure with stroke mortality were similar in cultures with different stroke mortality rates. Increases in blood pressure were associated with subsequent excess stroke mortality only in those who started from high usual levels; this study finds lower stroke risk in those men whose blood pressure increased moderately from low usual levels. Diastolic blood pressure is not independently associated with stroke risk in these populations.