Summary
Introduction:
Reports evaluating the association of stroke risk factors with incident stroke have generally assumed a uniform magnitude of associations across the age spectrum, an assumption we evaluated in this report.
Methods:
Participants enrolled between 2003 and 2007 in the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort study who did not have a stroke at baseline were followed for incident strokes. Associations of "traditional" stroke risk factors with incident strokes were assessed using: 1) proportional hazards analysis based on participant’s baseline age, and 2) Poisson regression analysis evaluating associations based on change in age of the participant during follow-up (“age of exposure”). In each analysis, age strata were selected to have a similar number of strokes in each stratum, specifically 45-64, 65-73, and 74+ years for the proportional hazards analysis; and 45-69, 70-79 and 80+ years for Poisson regression.
Results:
A total of 1,405 ischemic stroke events occurred among 28,235 participants during a median follow-up of 11.3 years with a total of 276,074 person-years of exposure. For both analytic approaches, the magnitude of the association with stroke was significantly smaller at older ages for diabetes (hazard or relative risk decreased from ≈2.0 in the younger strata to ≈1.3 in the younger strata). of older age), heart disease (from ≈2.0 to ≈1.3), and hypertension defined at a threshold of 140/90 mmHg (from ≈1.80 to ≈1.50); However, there were no age-related differences in the magnitude of the association between smoking, atrial fibrillation, or left ventricular hypertrophy .
Discussion:
Hypertension and diabetes are two of the most “important” risk factors for stroke; however, its association with stroke risk appears substantially lower at older ages. The fact that the magnitude of the association between smoking, atrial fibrillation, and LVH does not decrease with age suggests that their relative importance in determining stroke risk likely increases with age.
Comments
High blood pressure and diabetes are known risk factors for stroke, but now a new study shows that the amount of risk may decrease as people age. The study is published online in Neurology ®, the medical journal of the American Academy of Neurology.
"High blood pressure and diabetes are two important risk factors for stroke that can be controlled with medications, reducing a person’s risk," said study author George Howard, DrPH, of the School of Health. University of Alabama at Birmingham Public School. “Our findings show that its association with stroke risk may be substantially lower at older ages, although other risk factors do not change with age. These differences in risk factors mean that determining whether a person is at high risk for stroke may differ depending on their age .”
The study involved 28,235 people who had never had a stroke. Of this group, 41% were black and 59% were white. Participants were followed for an average of 11 years.
At the beginning of the study, participants were interviewed and underwent physical examinations to assess risk factors. Risk factors included high blood pressure, diabetes, smoking, atrial fibrillation, heart disease and left ventricular hypertrophy, which is thickening of the left ventricle of the heart. Because of the known higher risk of stroke in black people, race was also considered as part of the risk factors evaluated, Howard added.
Researchers followed participants every six months and confirmed strokes by reviewing medical records.
During the study, there were 1,405 strokes in 276,074 person-years . Person-years represent both the number of people in the study and the amount of time each person spends in the study.
The participants were divided into three age groups, which were then compared. The age ranges for those groups varied slightly depending on the data analyzed by the researchers. In general, the younger group included participants ages 45 to 69, the middle group included people ages 60 to 70, and the older group included people ages 74 and older.
The researchers found that people with diabetes in the youngest age group were about twice as likely to have a stroke as people of a similar age who did not have diabetes, while people with diabetes in the oldest age group were approximately 30% higher risk of having a stroke than people of similar age who did not have diabetes.
The researchers also found that people with high blood pressure in the youngest age group had an 80% higher risk of having a stroke than people of a similar age without high blood pressure, while the risk was reduced to 50%. for people with high blood pressure in the older age group compared to people of similar age without high blood pressure.
Additionally, when the researchers examined race as a risk factor, they found an increased risk of stroke for black participants in the youngest age group compared to white participants in that group. The racial difference decreased in the older age group. For stroke risk factors such as smoking, atrial fibrillation and left ventricular hypertrophy, the researchers found no age-related change in risk.
"It is important to note that our results do not suggest that treatment of high blood pressure and diabetes becomes less important in old age," Howard said. “Such treatments are still very important for a person’s health. But it may also be wise for doctors to focus on managing risk factors such as atrial fibrillation, smoking, and left ventricular hypertrophy as people age.”
Howard also noted that even when the impact of risk factors decreases with age, the total number of people with strokes at older ages could be higher , since the overall risk of stroke increases with age. For example, in the youngest age group for high blood pressure, researchers estimate that about 2.0% of people with normal blood pressure had a stroke, compared with 3.6% of people with high blood pressure. In the older age group, about 6.2% of people with normal blood pressure had a stroke, compared with 9.3% of people with high blood pressure.
One limitation of the research was that participants’ risk factors were assessed only once at the beginning of the study and may have changed over time.
The study was supported by the National Institutes of Health, including the National Institute of Neurological Disorders and Stroke and the National Institute on Aging.
