The study, by a team from the University of Michigan U-M Medical School and School of Public Health and the VA Center for Clinical Management Research, involved data from more than 4,900 people over the age of 65.
Two sources of information were utilized for the analysis. Detailed surveys and tests of memory and thinking speed over multiple years from participants in a large, national study of older Americans, and Medicare data from the same individuals.
Researchers focused on the 7.5 percent of black study participants, and the 6.7 percent of white participants, with no recent history of stroke, dementia or other cognitive issues, but who suffered a documented stroke within 12 years of their first survey and cognitive test in 1998.
Significantly Worse Test Scores
Through measurement of participants' changes in cognitive test scores over time from 1998 to 2012, the researchers observed that both blacks and whites did significantly worse on the test after their stroke than they had before.
Although the size of the effect was the same among blacks and whites, past research has shown that the rates of cognitive problems in older blacks are generally twice that of non-Hispanic whites. So the new results mean that stroke doesn’t account for the mysterious differences in memory and cognition that grow along racial lines as people age.
The researchers say the findings underscore the importance of stroke prevention. Lead author and U-M Medical School assistant professor Deborah Levine, M.D., MPH, said:
“As we search for the key drivers of the known disparities in cognitive decline between blacks and whites, we focus here on the role of ‘health shocks’ such as stroke. Although we found that stroke does not explain the difference, these results show the amount of cognitive aging that stroke brings on, and therefore the importance of stroke prevention to reduce the risk of cognitive decline."
Similar research on disparities in cognitive decline has focused on racial differences in socioeconomic status, education, and vascular risk factors such as diabetes, high blood pressure and smoking that can all contribute to stroke risk. These factors may explain some but not all of the racial differences in cognitive decline.
Levine and her colleagues note that certain factors, such as how many years a person has vascular risk factors, and the quality of his or her education, as well as genetic and biological factors, might play a role in racial differences in long-term cognitive performance.
But one thing is clear: strokes have serious consequences for brain function. On average, they rob the brain of eight years of cognitive health.
Therefore, people of all racial and ethnic backgrounds can benefit from taking steps to reduce their risk of a stroke. That includes controlling blood pressure and cholesterol, stopping or avoiding smoking, controlling blood sugar in diabetes, and being active even in older age.
D. A. Levine, M. Kabeto, K. M. Langa, L. D. Lisabeth, M. A. M. Rogers, A. T. Galecki. Does Stroke Contribute to Racial Differences in Cognitive Decline? Stroke, 2015; DOI: 10.1161/STROKEAHA.114.008156
“Background and Purpose—It is unknown whether blacks’ elevated risk of dementia is because of racial differences in acute stroke, the impact of stroke on cognitive health, or other factors. We investigated whether racial differences in cognitive decline are explained by differences in the frequency or impact of incident stroke between blacks and whites, controlling for baseline cognition.
Methods—Among 4908 black and white participants aged ≥65 years free of stroke and cognitive impairment in the nationally representative Health and Retirement Study with linked Medicare data (1998–2010), we examined longitudinal changes in global cognition (modified version of the Telephone Interview for Cognitive Status) by race, before and after adjusting for time-dependent incident stroke followed by a race-by-incident stroke interaction term, using linear mixed-effects models that included fixed effects of participant demographics, clinical factors, and cognition, and random effects for intercept and slope for time.
Results—We identified 34 of 453 (7.5%) blacks and 300 of 4455 (6.7%) whites with incident stroke over a mean (SD) of 4.1 (1.9) years of follow-up (P=0.53). Blacks had greater cognitive decline than whites (adjusted difference in modified version of the Telephone Interview for Cognitive Status score, 1.47 points; 95% confidence interval, 1.21 to 1.73 points). With further adjustment for cumulative incidence of stroke, the black–white difference in cognitive decline persisted. Incident stroke was associated with a decrease in global cognition (1.21 points; P<0.001) corresponding to ≈7.9 years of cognitive aging. The effect of incident stroke on cognition did not statistically differ by race (P=0.52).
Conclusions—In this population-based cohort of older adults, incident stroke did not explain black–white differences in cognitive decline or impact cognition differently by race.”
Photo: Laurentiu Huianu, Norfolk and Norwich University Hospitals NHSFT. Wellcome Images