"These studies were done with U.S. data, but they add weight to the global body of evidence around disadvantage and dementia risk, which is an issue governments around the world grapple with, and one that requires coordinated action", said Alzheimer's Association chief scientist Maria Carrillo.
This is the first study to look at racial disparity in the risk of incident dementia among this older population.
The two other studies found higher risk for dementia in people born in states marked by high infant mortality rates.
The subjects' average age was 58 and included 1,232 white Americans and 82 African Americans. During the period she focused on, the black infant mortality rate was almost twice as high as whites'.
There are now around 850,000 people in the United Kingdom with dementia.
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.
Dr Maria Carrillo, the chief science officer for the Alzheimer's Association, said: "The stressful events that the researchers were focusing on were a large variety... the death of a parent, abuse, loss of a job, loss of a home... poverty, living in a disadvantaged neighbourhood, divorce".
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The study did not look at the risk of dementia and experts said there could be many different factors at play.
The findings back up earlier studies that link stress and changes in the brain.
She and other researchers said the overall thrust of the studies' findings - which will be 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.
Stress in this study was defined as a sense of irritation, tension, nervousness, anxiety, fear or sleeping problems that last a month or more due to either work, health, family or other such problems.
The researchers said that each stressful experience was equivalent to approximately four years of cognitive aging in African Americans, compared with one-and-a-half years for whites.
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. But when those emotions become more frequent and chronic and interfere with daily life, then it can impact one's immune, metabolic and cardiovascular systems, as well as lead to a gradual decline of the brain's hippocampus - the crucial part of the brain responsible for long-term memory and spatial navigation.
Every year 25,000 new cases of dementia are diagnosed.