Harsh life experiences appear to leave African-Americans vulnerable to Alzheimer's and other forms of dementia, researchers reported Sunday at the Alzheimer's Association International Conference in London.
Several teams presented evidence that poverty, disadvantage and stressful life events are strongly associated with cognitive problems in middle age and dementia later in life among African-Americans.
The findings could help explain why African-Americans are twice as likely as white Americans to develop dementia. And the research suggests genetic factors are not a major contributor.
"The increased risk seems to be a matter of experience rather than ancestry," says Megan Zuelsdorff, a postdoctoral fellow in the Health Disparities Research Scholars Program at the University of Wisconsin-Madison.
Scientists have struggled to understand why African-Americans are so likely to develop dementia. They are more likely to have conditions like high blood pressure and diabetes, which can affect the brain. And previous research has found some evidence that African-Americans are more likely to carry genes that raise the risk.
But more recent studies suggest those explanations are incomplete, says Rachel Whitmer, an epidemiologist with Kaiser Permanente's Division of Research in Northern California.
Whitmer has been involved in several studies that accounted for genetic and disease risks when comparing dementia in white and black Americans. "And we still saw these [racial] differences," she says. "So there is still something there that we are trying to get at."
The research presented at the Alzheimer's conference suggests the missing factors involve adverse life experiences beginning in childhood. These experiences have already been linked to a range of diseases, including heart disease and cancer.
"We're starting to understand how early life stress and early life deprivation can increase your risk of a number of health outcomes in late life," Whitmer says. "And the latest thing is understanding how and why that might affect the brain."
Whitmer was part of a team that presented results of a study of more than 6,000 Kaiser Permanente health plan members, most born in the 1920s.
The team wanted to know whether people who grew 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 and limited access to medical care.
White people's risk of dementia wasn't affected by their place of birth. But black people were 40 percent more likely to develop dementia if they'd been born in a state with high infant mortality.
"These people left the state and subsequently moved to northern California, yet there was still this very robust association between being born in a state with high infant mortality and increased risk of dementia," Whitmer says.
Scientists from the University of Wisconsin presented results of a study of the link between stressful life events and mental function in middle age. They studied more than 1,300 people in their 50s and 60s, including 82 African-Americans.
Stressful experiences included having a parent with a drinking problem, financial insecurity, legal issues, divorce, being fired from a job, and the death of a child.
African-Americans reported 60 percent more of these stressful events than white Americans. But that was only part of the difference, Zuelsdorff says.
"The impact of these stressful events was stronger in African-Americans than it was in non-Hispanic white participants," she says.
The researchers discovered this by administering tests that reveal the brain's speed and flexibility in doing certain tasks. These abilities normally decline with age. So the team looked for evidence that stressful events were accelerating this decline.
And they found that in white participants, each stressful event added about a year and a half to normal brain aging. But in African-Americans, each event aged the brain an extra four years.
The next challenge for researchers is to figure out precisely how adverse life experiences are changing the brain, Zuelsdorff says. That will mean looking at the effects of stress hormones and seeing whether stress leads to inflammation in the brain, something that has been associated with Alzheimer's.
It's summertime. And if you have a young kid, chances are they're covered in a film of sweat and dirt. It can be kind of gross. We went to New York Avenue Park in Washington, D.C., and asked parents how comfortable they are with the yucky stuff.
JEANINE MCGINNISS: Probably I was a little bit more of a germ freak. And then once you have a kid, you start getting comfortable with more germs.
DOROTHEA THOMAS: You know, every possible chance that if there is a germ or whatever, I make him wash his hands.
GERALD SMITH: Make sure they wash their hands constantly, all the time, soap and water.
GARCIA-NAVARRO: A quick survey there of parents Jeanine McGinniss, Dorothea Thomas, Wendy Christmas, and Gerald Smith. But are we too quick to rush kids to the bath at the end of the day? Our next guest says that dirt is good. Dr. Jack Gilbert is professor of surgery at the University of Chicago, and he's co-author of a book for new parents guiding them through the world of germs, the microbiome and obviously dirt. He joins us from our member station WBEZ in Chicago. Good morning.
GILBERT: Well, as a parent - I have two children now - I can say that when I had my first child, I got a lot of different advice on the kinds of things that I should do to look after my kid. If they have a snotty nose, consider taking antibiotics, to make sure their pacifier was always sterilized, to sterilize their food and make sure it was always boiled before you gave it to them. And so for me, it was interesting to go back and look at the data, especially after my second child, where I got a lot more lax in terms of how much of that preparation I put in.
And so we went and looked at the literature, went and delved into the science and tried to understand what we actually knew about the risks that our modern-day children could experience from those kinds of exposures. Turned out that most of the exposures were actually beneficial.
GARCIA-NAVARRO: You mentioned a few of them already, but what are some of the main things that parents get wrong?
GILBERT: Some of the main things are over-sterilizing their environment, keeping their children from ever getting dirty. So going out into the backyard and playing in the mud, and then as soon as they're filthy, bringing them in and sterilizing their hands with antiseptic wipes and then making sure that none of the dirt gets near their faces. Also keeping them away from animals. It's fine to wash their hands if there's a cold or a flu virus around. But if they're interacting with a dog and the dog licks their face, that's not a bad thing. In fact, that could be extremely beneficial for the child's health.
GARCIA-NAVARRO: Let's get to some of these questions. You tell me good or bad. Hand sanitizer?
GILBERT: Usually bad. Hot soapy water is fine, even mildly warm soapy water is fine. And it's actually probably less damaging to the child's overall health.
GARCIA-NAVARRO: All right, five-second rule. If something falls on the ground, you know, that thing if it's there for under five seconds it's clean, if it's over five seconds you've got to wash it.
GILBERT: The five-second rule doesn't exist. It takes milliseconds for microbes to attach themselves to a sticky piece of jammy (ph) toast, for example. But it makes no difference. Unless you dropped it in an area where you think that could be a high risk of extremely dangerous pathogens, which in every modern American home is virtually impossible, then there's no risk to your child.
GARCIA-NAVARRO: All right. Wash a pacifier or lick it if it falls on the ground?
GILBERT: Lick it every time. A study of over 300,000 children showed that parents that lick the pacifier and put it back in, their kids developed less allergies, less asthma, less eczema. Overall, their health was stronger and more robust.
GARCIA-NAVARRO: And how often should I give my daughter a bath? This is a very important question, by the way, because she hates them.
GILBERT: I know, exactly. Especially when they're small children under the age of 6 months, so infants up to about 18 months, you don't need to get them off every day. In fact, you could go for a couple of days. Wiping down the area with a warm wet cloth. Overall, over-washing can actually damage the skin and lead them to have a higher likelihood of infections and over-inflammatory reactions like eczema.
GARCIA-NAVARRO: One of the things that we are seeing, especially in America, is the rise of allergies. Do you think these two things are linked because we try to protect them so much that, you know, the unintended consequence of that is that actually they are more susceptible to things like allergies?
GILBERT: Absolutely. So the basic premise is that in the past, we would have eaten a lot more fermented foods, which contain bacterial products and bacteria. We would have allowed our children to be exposed to animals and plants and soil on a much more regular basis. Now we live indoors. We sterilize our surfaces. Their immune systems then become hyper-sensitized.
You have these little soldier cells in your body called neutrophils. And those neutrophils, when they spend too long going around looking for something to do, they become grumpy and pro-inflammatory. And so when they finally see something that's foreign, like a piece of pollen, they become explosively inflammatory. They go crazy, right? And that's what triggers asthma and eczema and oftentimes food allergies.
GARCIA-NAVARRO: So I was going to ask you just finally to give us some advice. I mean, as a mother, what should I be allowing my daughter to do? And what is still something that I should not allow her to do?
GILBERT: Right. So oftentimes, it's hard to get your kids to eat a healthy diet, right? I know this more than any parent. But I would strongly try and encourage the consumption of more colorful vegetables, more leafy vegetables, a diet more rich in fiber, as well as reducing the sugar intake. But just generally, allow your kid to experience the world. As long as they're properly vaccinated, there's no threat. And they will actually get a stronger, more beneficial exposure.
GARCIA-NAVARRO: Dr. Jack Gilbert. He's the co-author of "Dirt Is Good." Thank you so very much.
(SOUNDBITE OF PENGUIN CAFE ORCHESTRA'S "DIRT") Transcript provided by NPR, Copyright NPR.