Public Release: 

Stroke Incidence Significantly Higher Than Previously Estimated

NIH/National Institute of Neurological Disorders and Stroke

A new study (1) by researchers at the University of Cincinnati Medical Center suggests that the number of strokes in the United States may be dramatically higher than previously estimated. According to the study, approximately 700,000 strokes occur in the United States every year. This new estimate is 200,000 strokes higher than the previous estimate of 500,000 strokes a year.

A team of investigators led by Joseph Broderick, M.D., recalculated the commonly cited figures on how many people suffer a stroke by including recurrent strokes in their estimate and by adjusting the total numbers to reflect an older, more diverse U.S. population. The preliminary results of their study, funded by the National Institute of Neurological Disorders and Stroke (NINDS), are published in the February 1998 issue of Stroke: A Journal of the American Heart Association.

"These investigators have used recent data, taking into account an increasing and diverse population that is living longer. We can now estimate that many more Americans suffer from stroke than was previously believed," said Michael D. Walker, M.D., Director of the NINDS Division of Stroke, Trauma, and Neurodegenerative Disorders. "It is now more essential than ever to develop safe and effective treatments for stroke, a devastating disorder and the third leading cause of death in the United States."

The Greater Cincinnati / Northern Kentucky Stroke Study is the first study of stroke in a racially diverse, large metropolitan community since the advent of modern brain imaging. For the past 45 years the primary data on the incidence of stroke have come from the small, middle-class population of Rochester, Minnesota. Another well-known measurement of stroke incidence is based on a study population in Framingham, Massachusetts. The Framingham Study produced the data used to arrive at the estimate of 500,000 strokes in the United States each year.

The Cincinnati investigators focused their research on Greater Cincinnati / Northern Kentucky, an area in which the population is representative of the United States population in terms of age, economic status, and proportion of African Americans. In the current volume of Stroke, the investigators report their preliminary data on the total number of strokes that occurred during 6 months in African Americans in the Greater Cincinnati / Northern Kentucky metropolitan area.

The Cincinnati researchers included strokes in individuals who have experienced more than one stroke. Both the Rochester study and the Framingham Study counted only the number of first-time strokes, a traditional method of epidemiological study. Yet, people who suffer strokes frequently experience more than one stroke, and their recurrent strokes are often more disabling and deadly than their first stroke.

Between January 1 and June 30, 1993, Dr. Broderick and his colleagues enrolled 332 African American stroke patients into the study. They found that the overall incidence rates for all first-ever strokes among blacks in the study was 288 per 100,000. This contrasts to an overall rate of only 179 per 100,000 of first-ever strokes in Rochester between 1985 and 1989. This incidence rate in blacks in Greater Cincinnati was 1.6 times greater than the reported incidence rate of stroke among the population of Rochester. The incidence rate for all stroke, including first-time and recurrent, for African Americans in the Cincinnati area during the study period was 411 per 100,000. Extrapolating from these data, the Stroke authors estimate that during 1996 there were 138,100 strokes among blacks and 593,000 strokes among whites and other minority segments of the population, for a total of 731,100 first and recurrent strokes in the United States.

"Even this figure might be low because in this part of the study we weren?t counting strokes in African Americans who never came into the hospital," said Dr. Broderick.

The study also points out that current statistics underestimate the burden of stroke among younger African Americans. Although the rate of stroke among those older than 65 is largely similar for both blacks and whites, blacks under the age of 65 in the Greater Cincinnati study experienced two to four times more first strokes compared to whites of the same age in the Rochester study.

"This study points up the critical need for studies of a wide variety of communities in order to determine the true burden of stroke in this country, " said Dr. Broderick. "Especially now with the advances in medical treatment, we must have as much information as possible about how frequently stroke occurs and the causes of stroke in various segments of the population."

Possible explanations for the higher stroke rates in African Americans are a higher prevalence of hypertension and diabetes, higher rates of smoking among the young population, and a lower and more stressful socioeconomic lifestyle, according to the study authors.

A stroke occurs when blood flow to the brain is cut off. In order to lend urgency to the public education message that stroke is a treatable condition, some organizations have been calling stroke a "brain attack." Stroke remains the third leading cause of death in this country after heart disease and cancer, and the leading cause of adult disability.

On February 6, 1998, Dr. Broderick and his colleagues will present their results at a press conference in Orlando at the 23rd International Joint Conference on Stroke and Cerebral Circulation sponsored by the American Heart Association.

The NINDS, one of the National Institutes of Health located in Bethesda, Maryland, is the nation?s leading supporter of research on the brain and nervous system and a lead agency for the Congressionally designated Decade of the Brain.

(1) Broderick, J., Brott, T., Kothari, R., Miller, R., Khoury, J., Pancioli, A., Gebel, J., Mills, D., Minneci, L., and Shukla, R. "The Greater Cincinnati / Northern Kentucky Stroke Study: Preliminary First-Ever and Total Incidence Rates of Stroke Among Blacks." Stroke, Vol. 29, No. 2; February 1998.

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