The results showed that a larger number of stressful events was linked to poorer cognitive function in later life.
"Not one of these things is good news - except that they are modifiable", Zuelsdorff said. African Americans are twice as likely to develop dementia as white Americans, which researchers previously attributed to genetics and conditions such as obesity, diabetes, and cardiovascular disease, reports the Washington Post.
Another study from the University of Wisconsin found that people in disadvantaged neighborhoods had disproportionately higher levels of biomarkers linked to Alzheimer's disease, which is the most common form of dementia.
African Americans born in those states had a 40 percent higher risk of dementia than black people who were born elsewhere. This is the first study to look at racial disparity in the risk of incident dementia among this older population.
The researchers have mapped over 30 million neighborhoods in the U.S. based on socioeconomic data and then analyzed it against available information on Alzheimer's disease patients.
And a third study of almost 1,500 people by another group of researchers at the University of Wisconsin found "markedly worse" cognitive performance, based on tasks such as verbal learning, immediate memory and speed and flexibility of cognition, in people from the most disadvantages neighbourhoods.
Those who had more such problems scored worse on cognitive tests, scientists told the Alzheimer's Association International Conference in London yesterday.
A second study found that rates of dementia were higher among African Americans in states with a high infant mortality rate when compared with white counterparts, suggesting the long term impact on the brain of early events.
"This linkage between neighborhood disadvantage and Alzheimer's has never been explored until our work", said Amy J. Kind, a physician and researcher at the University of Wisconsin. For the past year or so, she focused on how that would intersect with race. The findings back up earlier studies that link stress and changes in the brain. The others were non-Hispanic whites.
The subjects underwent testing of their memory and executive function.
"We're trying to get at really, potentially disruptive events", Zuelsdorff said in an interview.
Findings of new studies that looked at racial disparities in patients with Alzheimer's disease have found evidence suggesting that social conditions such as stress of poverty and racism can increase risk of dementia in African Americans.