Stroke incidence and mortality correlated to stroke risk factors in the WHO MONICA Project. An ecological study of 18 populations.

Background: The aim of the present study was to determine the extent to which the variation in conventional risk factors contributed to the variation in stroke incidence among these populations.

Methods: Within the WHO MONICA Project, stroke has been recorded in 18 populations in 11 countries. In population surveys, risk factors for cardiovascular diseases have been examined in the age group 35 to 64 years. Over a 3-year period, 12,224 acute strokes were registered in men and women within the same age range.

Results: The highest stroke attack rates were found in Novosibirsk in Siberia, Russia, and Finland, with a more than three-fold higher incidence than in Friuli, Italy. The mean diastolic blood pressure among the populations differed by 15 mm Hg between Novosibirsk (highest) and Denmark (lowest). In multiple regression analyses, the presence of conventional cardiovascular risk factors (smoking and elevated blood pressure) explained 21% of the variation in stroke incidence among the population in men and 42% in women. In Finland, in China, and in men in Lithuania, the stroke incidence rates were higher than expected from the population risk factor levels.

Conclusion: Prevalence of smoking and elevated blood pressure explain a substantial proportion of the variation of stroke attack rates between populations. However, other risk factors for stroke that were not measured in the present study also contribute considerably to interpopulation differences in stroke rates.