Mexican-Americans have a far higher chance of suffering a stroke than non-Hispanic whites, according to a new study led by a University of Michigan stroke specialist.
And, according to a second study published today by the same team, the difference doesn't appear to be related to Mexican-Americans' higher incidence of diabetes, which had been thought to raise their risk of a certain type of stroke.
It's the first time that the stroke gap between the two groups has been demonstrated, and has far-reaching implications for educating Mexican-Americans about preventing strokes and acting quickly when one strikes. It also raises questions about factors that might be contributing to the difference in risk.
The two new studies, published in the Aug. 15 issue of the American Journal of Epidemiology and the Aug. 10 issue of Neurology , come from an in-depth population-based project funded by the National Institutes of Health and called BASIC, for Brain Attack Surveillance in Corpus Christi .
BASIC uses medical records and interviews to study strokes among people in Neuces County, Texas, home to a large population of second- and third-generation Mexican-Americans and many non-Hispanic whites. In all, 2,350 validated strokes and near-strokes occurring in the years 2000 through 2002 were studied.
Lead author Lewis Morgenstern, M.D., who directs the U-M Stroke Program and the BASIC study, calls the results a “wake-up call to the country” about the third-leading cause of death and leading cause of disability in the nation. Mexican-Americans make up two-thirds of Hispanics, the nation's largest minority group.
“This is a best-case scenario population of Mexican-Americans, who have been in this country for several generations and have few cultural and language barriers to getting medical care,” he says. “If their risk of stroke is this much higher than that of their non-Hispanic white neighbors, especially in their younger years, this is the tip of the iceberg for the nation's broader Mexican-American community as it grows older.”
Morgenstern, an associate professor of neurology at the U-M Medical School, started the BASIC study while he was at the University of Texas Medical School at Houston and the University of Texas School of Public Health at Houston. Several authors on the new papers are from those schools, and one is at the University of Pittsburgh.
The study shows that Mexican-Americans aged 45 to 59 were twice as likely as their non-Hispanic white counterparts to have any sort of stroke or near-stroke, and those in their 60s and early 70s were about 60 percent more likely to have a stroke or near-stroke, according to the study published in the American Journal of Epidemiology .
The researchers also broke stroke risk down by type: ischemic, in which a blood vessel in the brain is blocked; transient ischemic attack, which is a temporary blockage; and two kinds of hemorrhagic, or bleeding, strokes — intracerebral and subarachnoid, which occur in different parts of the brain.
The rates of ischemic stroke, adjusted for age according to Nueces County 2000 Census figures, was twice as great for Mexican-Americans aged 45 to 59 as for non-Hispanics, and about 60 percent greater for those aged 60 to 74. There was little difference among those aged 75 and older.
Younger Mexican-Americans also had twice the risk of non-Hispanic whites of suffering a TIA, a warning sign for a future full-blown stroke. The odds were about even for those in their 60s and 70s.
For bleeding strokes, there were differences between the two groups across the board, adjusted for age. In particular, Mexican-Americans in their late 40s through their 50s were three times as likely as non-Hispanic whites in the same age group to suffer an intracerebral hemorrhage, and Mexican-Americans aged 60 to 74 years were more than twice as likely as their white counterparts to have a subarachnoid hemorrhage.
Why all the differences between the two groups? Morgenstern notes that Hispanics are known to have a high rate of diabetes, which increases stroke risk, but they have similar rates of two other major risk factors — high blood pressure and high cholesterol — as non-Hispanic whites.
The diabetes difference has prompted many stroke specialists to speculate that Hispanics might have a higher risk of ischemic stroke involving blockages in the smaller blood vessels, which can be brought on by the damage caused by high blood sugar.