A new group of studies into racial disparities among people with Alzheimer’s disease suggests that social conditions, including the stress of poverty and racism, substantially raise the risks of dementia for African Americans.
In four separate studies, researchers found that conditions that affect blacks disproportionately compared with other groups — such as poor living conditions and stressful events such as the loss of a sibling, the divorce of one’s parents or chronic unemployment — have severe consequences for brain health later on.
One study by University of Wisconsin researchers found that stress literally takes years off a person’s life in terms of brain function — an average of four years for African Americans, compared with 1½ years for whites.
Another Wisconsin study showed that living in a disadvantaged neighborhood is associated with later decline in cognitive function and even the biomarkers linked to Alzheimer’s disease, which is the most common form of dementia.
In the other two studies, researchers with Kaiser Permanente and the University of California at San Francisco found a higher degree of dementia risk for people born in states with high rates of infant mortality. Researchers at Kaiser Permanente and the University of California at Irvine found that racial disparities in the incidence of dementia that were previously found among people who are 65 years and older also appear in the very oldest demographic, people who are 90 or older.
These lifelong effects of stress and disadvantage could be direct, perhaps in line with previous research showing that sustained stress can physically alter the brain. Or the impact could be the result of cascading effects, such as when a powerfully disruptive event affects a person’s early schooling and limits achievement later on.
“No one’s looking at the same kind of things, but the research all dovetails really well,” said Megan Zuelsdorff, an epidemiologist with the University of Wisconsin School of Medicine and Public Health. “It is the social environment that’s contributing to disparities.”
She and other researchers said the overall thrust of the studies’ findings — which were presented Sunday in London at the Alzheimer’s Association’s annual conference — not only offers additional evidence of racial inequities in people’s risk of dementia but suggests the need for more urgent interventions directed at those communities.
“Not one of these things is good news — except that they are modifiable,” Zuelsdorff said.
Over the years, researchers have theorized that blacks are more susceptible to Alzheimer’s owing to genetics and higher rates of obesity, diabetes, hypertension and cardiovascular disease.
But researchers in recent years have also been focused on social factors that might raise the risk. It’s long been known that stress is associated with social disadvantage, and in the United States and other countries, members of minority groups often suffer disproportionately from those disadvantages.
Paola Gilsanz, a researcher with the University of California at San Francisco and Kaiser Permanente’s Division of Research, attempted to examine the impact on brain health on people who had been born in states with high levels of infant mortality, a sort of proxy for beginning life under adverse circumstances. During the period she focused on, the infant mortality rate of blacks was nearly twice as high as that of whites.
The study reviewed clinical exam data collected between 1964 and 1973 for 6,284 Kaiser Permanente members, of whom 17 percent were black. The subjects were born between 1919 and 1932.
Researchers then analyzed their health records in regard to whether they had been born in one of 10 states with the highest infant mortality rates in 1928 — a year chosen because of the stark difference between white and black infant mortality rates and that year’s place toward the lower range of ages among the subjects of the study.
African Americans born in those states had a 40 percent higher risk of dementia than blacks who were not born in states with high infant mortality rates. The risk was twice as high, even after accounting for differences in education and other health risk factors, as it was for whites born outside states with high infant mortality rates.
“I think this is important because it contributes more information to a growing body of evidence that early life matters to brain health and that maybe early life conditions partially explain the racial disparities we see in dementia risk,” Gilsanz said. “We should really think about brain health as a lifelong concern.”
Amy J. Kind, who is also a physician and researcher at the University of Wisconsin, looked to see whether there is a relationship between disadvantaged neighborhoods and disparities in the prevalence of dementia.
She and her colleagues first refined Census and American Community Survey data to map more than 34 million neighborhoods — blocks of 1,500 to 3000 people — based on socioeconomic data to arrive at an Area Deprivation Index. After ranking those blocks from least disadvantaged to most, the researchers compared them with data of nearly 1,500 people who had been tested for memory and cognitive function in the Wisconsin Registry for Alzheimer’s Prevention Study (WRAP). The group also analyzed the neighborhood data against a much smaller subset of people who had been tested for biomarkers — proteins found in cerebrospinal fluid linked to Alzheimer’s.
The researchers found that people in the most disadvantaged neighborhoods performed significantly worse in every aspect of cognitive function that was tested; they also had disproportionately higher levels of an Alzheimer’s biomarker.
“This linkage between neighborhood disadvantage and Alzheimer’s has never been explored until our work,” Kind said.
Zuelsdorff — the University of Wisconsin School epidemiologist whose study found that higher levels of stress among African Americans have the effect of speeding the aging of a person’s brain — has spent a decade or more looking at how stressful experiences affect cognitive abilities. For the past year or so, she focused on how that would intersect with race.
Using data from the WRAP, Zuelsdorff and her colleagues examined the role of profound stress on the cognitive function of 1,320 people, of whom 82 were black. The others were non-Hispanic whites. Although the subjects differed in race, they were otherwise alike in terms of average age, genetic disposition as regards Alzheimer’s risk, and education.
The subjects underwent testing of their memory and executive function. The impact of stress in their lifetimes was elicited through a questionnaire on 27 items, such as whether the person had severe problems in school, the family suffered bankruptcy or a parent suffered from alcohol-related problems. Although the questionnaire also asked respondents to rank the impact of those disruptive events, Zuelsdorff’s study focused only on the number of such events themselves.
“We’re trying to get at really, potentially disruptive events,” Zuelsdorff said in an interview.
What the study found was that blacks reported more than 60 percent such stressful events in their lifetimes and that those experiences were associated with poorer cognitive function.