LULU GARCIA-NAVARRO, HOST:
Staying with health care, we turn now to a new report on Alzheimer's disease. African-Americans are twice as likely to develop Alzheimer's or some other form of dementia compared to those who are white. NPR's Jon Hamilton reports on new research that's helping to explain the disparity.
JON HAMILTON, BYLINE: Scientists have struggled to understand why African-Americans have such a high risk of dementia. As a group, they are more likely to have conditions like high blood pressure and diabetes, which can affect the brain. And there is some evidence that genetic factors play a role. But Rachel Whitmer of Kaiser Permanente's Division of Research in Northern California says her own research shows that those explanations are incomplete.
RACHEL WHITMER: These risk factors were taken into account, and we still saw these differences. So there is still something there that we are trying to get at.
HAMILTON: So Whitmer and other researchers have been looking at less obvious risk factors like stress and poverty. She says it's already clear that children who grow up in a harsh environment are more likely to have health problems like diabetes and heart disease.
WHITMER: We're starting to sort of understand how early life stress and early life deprivation can increase your risk of a number of health outcomes in later life. And I think the latest thing now is understanding how and why that might affect the brain.
HAMILTON: Whitmer was part of a team that studied more than 6,000 Kaiser Permanente health plan members in their 80s and 90s. The team wanted to know whether people who'd grown up in harsher conditions were more likely to develop dementia, so they looked at people who'd been born in states with high infant mortality rates, an indicator of social problems like poverty. They present their results today at the Alzheimer's Association International Conference in London. The study found that white people's risk of dementia wasn't affected by their place of birth, but Whitmer says black people were 40 percent more likely to develop dementia if they'd been born in a state with high infant mortality.
WHITMER: These people left the state and subsequently moved to Northern California, yet there still was this very robust association between being born in a state with high infant mortality and an increased risk of dementia.
HAMILTON: A separate study looked at the link between stressful life events and mental function in middle age. Megan Zuelsdorff from the University of Wisconsin in Madison says participants answered questions like...
MEGAN ZUELSDORFF: When you were a child, did a parent drink so much that it caused problems? Did your parents divorce? Did you have trouble in school?
HAMILTON: Zuelsdorff says participants also reported stressful experiences they had as adults, things like a serious illness or the death of a child. And African-Americans reported 60 percent more stressful events than white Americans, Zuelsdorff says that was only part of the difference.
ZUELSDORFF: The impact of these stressful events was stronger in African-Americans than it was in non-Hispanic white participants. Each stressful event is more detrimental.
HAMILTON: The researchers tested the brain speed and flexibility, things that normally decline with age. The test showed that in white participants, each stressful event added about a year and a half to normal brain ageing. In African-Americans, each event added about four years. Zuelsdorff says this all may sound discouraging, but it also means there's a possible solution.
ZUELSDORFF: The increased risk seems to be a matter of experience, rather than ancestry. And this is something we can change.
HAMILTON: In other words, by improving the early lives of African-Americans, it may be possible to reduce the risk of dementia later on. Jon Hamilton, NPR News.