The incidence of stroke has decreased since 1950, according to the latest data from the long-running Framingham study (JAMA 2006;296:2939–2946). However, the lifetime risk for individuals who are 65 years old today is virtually unchanged from the 1950 figure of their age-matched counterparts.
These apparently contradictory findings highlight the conflict of preventing serious disease in a population that is aging and at increased risk of these diseases, according to study author Sudha Seshadri, MD, assistant professor of neurology at Boston University. She noted that the senior investigator, Philip A. Wolf, MD, a professor of neurology at Brown, has spearheaded the Framingham Study stroke research since 1967.
Investigators evaluated the data from 9,152 men and women who had enrolled in the study and were free of stroke at the time of enrollment. The participants included the original enrollees who had been recruited in 1948 and also their offspring and spouses. They examined stroke incidence and lifetime stroke risk in three periods: 1950 to 1977, 1978 to 1989, and 1990 to 2004, recording baseline characteristics at age 65 years in each period.
The age-adjusted incidence of first stroke for men was 7.6 per 1,000 in 1950 to 1977; 6.2 per 1,000 for 1978 to 1989; and 5.3 per 1,000 for 1990 to 2004, a statistically significant decrease (p= 0.02). For women in the corresponding periods, the incidences were 6.2, 5.8, and 5.1, a decrease that was also statistically significant (p= 0.01).
However, the lifetime risk, which also declined, did not decrease in a significant manner. Men's lifetime risk of stroke at the age of 65 was 19.5 percent in 1950 and 14.5 percent in 2004; for women of that age, the lifetime risk was 18 percent in 1950 and 16.1 percent in 2004.
INCREASED LONGEVITY LEADS TO DELAYED STROKE
“Stroke is delayed because people live longer and have strokes later in life,” said Dr. Seshadri. However, stroke severity was similar in all time periods, and the 30-day mortality after the stroke for men decreased significantly, from 23 percent to 14 percent, although women's risk of dying within the 30-day period after a stroke was virtually the same throughout the study period: 21 percent in 1950 and 20 percent in 2004.
“There has been some progress, but we need to continue our efforts with prevention,” she said. “We need to increase efforts to improve survival after stroke, and we particularly need to address the difference in stroke survival for men and women.”
Several stroke experts, who were not involved with the current study, agreed with the observations about stroke in an aging population, but some noted a few limitations of the current data.
“The limitation, ironically, is that the Framingham data largely reflects a well-educated, middle-class, white population,” said Larry B. Goldstein, MD, director of the Duke Center for Cerebrovascular Disorder and the Duke Stroke Center. “We need to be cautious about generalizing these findings to the rest of the population, but the observations are still important.”
Increasing life expectancy could well explain the enigma of a decreasing incidence and a virtually unchanged lifetime risk, he said. “With all of these studies, one thing we're trying to get at is the burden of disease,” he said. “Given the aging of the population, the burden of stroke on the population may be increasing.”
The study underscores the need to focus on stroke treatment and post-stroke recovery as well as prevention, he said.
University of Cincinnati neurology chair Joseph Broderick, MD, agreed with Dr. Goldstein that the data are important but limited. “The study took place over a long time and confirms other research data that had showed a decline of stroke incidence up to the 1980s,” he said. Using a biracial population of 1.3 million in Greater Cincinnati, Dr. Broderick and colleagues compared the periods 1993 to 1994 and 1999. The stroke rate was virtually unchanged in those periods: 158 per 100,000 for both time periods (Stroke 2006;37(10):2478–2478).
“The Framingham study is limited in its ability to comment on changes in the last 15 years because they have had a relatively small number of documented strokes in their cohort,” he said. For example, in a 15-year period, 1990 to 2004, there were only 148 strokes in men. In our Greater Cincinnati population during 1999, there were over 2,000 first-ever strokes, six times as many strokes as in the Framingham study in more than 15 years.
“The Framingham study is a terrific resource to study stroke rates over time, but we need to view it from the perspective of its limits in size and recruitment methods,” he said. “For example, it provides us no data regarding African-Americans and Hispanics.”
RISK FACTORS FOR STROKE
Dr. Broderick noted that the Framingham Study also showed an increase in some stroke risk factors. “There is more obesity, more diabetes, and there has not been much of a decrease in the rate of smoking in our population during the last 10 to 15 years,” Dr. Broderick said. “These are the major stroke risk factors, and the lack of progress in these areas may explain why the stroke rate is not going down.”
Although the efforts to intervene medically and prevent recurrent strokes have been commendable, primary prevention is still the battleground, he said. “Most strokes are first strokes,” he said. “Therefore, lifestyle changes are critical for reducing stroke incidence.”
Another issue that may promote lifetime stroke risks could be, ironically, some victories in heart disease. “Patients are surviving cardiac disease and atrial fibrillation, but these conditions leave them at risk for stroke,” he said. “We're victims of our own successes.”
Ralph L. Sacco, MD, director of stroke and critical care and professor of neurology in Columbia University in New York, said: “We're making some headway in prevention, but the aging of our population means we will be faced with caring for more people with stroke. Stroke is still a major public health burden.” He urged investigators to explore further some of the other implications of the current study. “We also need to look at gender issues such as the lifetime risk of stroke for men and women. At age 65, the risk of stroke was greater for women than men.” Because women tend to live longer, the lifetime stroke risk may be affected and the stroke burden among women will be greater, he said.
“Still, we need to note several things about the Framingham Study,” he said. “It's hard to compile outstanding data like these for such a long period of time. That's the beauty of the Framingham Study!”
ARTICLE IN BRIEF
An analysis of data from the long-running Framingham study shows that the incidence of stroke has decreased since 1950, but lifetime risk for individuals who are 65 years old today is virtually unchanged from the 1950 figure of their age-matched counterparts. Experts say the data point to the burden of stroke in an aging population and the need for improved prevention efforts.
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