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 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.
A 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 11/2 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 another study, 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.
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 — presented Sunday in London at the Alzheimer's Association's annual conference — not only offer additional evidence of racial inequities in people's risk of dementia but suggest 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.
Researchers in recent years have focused on social factors that might raise the risk of dementia. 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 disproportionally 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 of people who had been born in states with high levels of infant mortality, a sort of proxy for beginning life under adverse circumstances. 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.
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.
Amy J. Kind, 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 3,000 people — based on socioeconomic data to arrive at an Area Deprivation Index. After ranking those blocks from least disadvantaged to most, the researchers then compared them with the Wisconsin Registry for Alzheimer's Prevention Study, or WRAP, data of nearly 1,500 people who had been tested for memory and cognitive function. 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.