Risk factors for stroke.

Stroke is the third leading cause of death in the United States and the major cause of adult neurological disability. In 1991, approximately 500,000 Americans had a stroke and more than 142,000 died from stroke. In that year, there were more than 3,000,000 stroke survivors in the United States (1). Stroke mortality varies widely in different countries around the world, and these differences provide evidence that environmental influences are important in the development of stroke. Among 33 industrial countries, the United States has one of the lowest stroke death rates while Eastern European countries and Portugal have among the highest rates. Other indicators supporting the importance of environmental influences in stroke incidence or mortality include: geographic variation in stroke deaths; variability according to specific geographic regions; variation in rates by sex and race; and changes in stroke occurrence over time. Death rates for stroke in the United States have declined steadily since 1915. This decline has been consistent in that it has occurred in all age groups, in both races and sexes, and in all regions. The rate of decline before 1968 averaged 1% per year. This was before the advent of modern medicine—effective antihypertensive agents did not become available until the 1960s—and many believe the decline in stroke mortality mirrored the decline in death rates generally. The evidence strongly supports a link to improved hygiene, nutrition, and public health rather than to improved medical care. From 1972 to 1992 in the United States, the pace of decline of mortality from stroke accelerated, falling more than 5% per year or 60% in two decades. Similar declines have also occurred in most other westernized industrial nations. Although the mechanism for this decline in death rates is not entirely clear, recent data suggest it is due largely to a decrease in stroke severity, although a declining stroke incidence has occurred in some populations.