The observation doesn't prove DDT causes
Alzheimer's, or that people who have been exposed to the chemical
will develop the degenerative brain disease, they said.
But in the complex picture of Alzheimer's — which has many potential
genetic and lifestyle contributors — this may be one more piece to
consider, according to lead author Jason Richardson.
"If there was a single environmental factor that was contributing to
any (neurologic) diseases . . . that kind of thing is very easy to
find. That's not what we're saying here," said Richardson, from the
Rutgers Robert Wood Johnson Medical School in Piscataway, New
"More than likely you're looking at complex gene-environment
interactions. What we found really gives us a starting off point,"
he told Reuters Health. "Now we can use that information to try to
understand who is at risk, when and ultimately, why."
DDT was banned in the U.S. in the 1970s, but is still used in some
other countries. The World Health Organization supports using the
pesticide to help eradicate malaria under certain circumstances.
In a prior small study, Richardson and colleagues had found levels
of DDE — a broken-down form of DDT — were higher than usual in the
blood of people with Alzheimer's disease.
To learn more, they analyzed blood samples from 86 people with
Alzheimer's and 79 people without the disease.
On average, DDE levels were almost four times higher among people
with Alzheimer's than in the comparison group, the researchers
found. DDE was detected at any level in 80 percent of people with
Alzheimer's and in 70 percent of people without Alzheimer's,
according to findings published in JAMA Neurology.
A follow-up lab experiment suggested that DDE increases levels of a
protein that is known to result in the brain plaques seen in
Alzheimer's patients, Richardson said.
But that still leaves many questions unanswered, he noted.
"Obviously we want to replicate this with a much larger number of
samples and people," Richardson said.
The researchers also plan to explore DDE in other populations, since
the participants in this study were generally patients at
Alzheimer's treatment centers and their family members.
[to top of second column]
Alzheimer's disease researcher Kathleen Hayden of Duke University
in Durham, North Carolina, said studies that measure DDE levels in
large groups of healthy people would also be helpful. "We'd want to
follow people prospectively and see whether or not they develop
dementia," Hayden, who wasn't involved in the new study, told
In an editorial, two neurologists point out there are no data to
suggest that regions of the world where people have very high levels
of DDE also have more Alzheimer's disease.
"These conclusions should be considered as preliminary until there
is independent confirmation in other populations," write Dr. Steven
T. DeKosky of the University of Virginia School of Medicine in
Charlottesville and Dr. Sam Gandy from the Mount Sinai Alzheimer's
Disease Research Center in New York.
For now, calling DDE a marker for who is at risk of Alzheimer's
is "going just a step too far," Hayden agreed.
"DDT exposure is not destiny that you're definitely going to get
Alzheimer's disease. These are things that might increase your
risk," she said.
Still, she thinks there is reason to be wary of DDT and related
"These agents affect the central nervous system. That's a reason why
they should be of interest to people who study neurodegenerative
diseases," Hayden said.
"For myself, I'm concerned that pesticides are used in such
abundance these days, and we don't really know what the effects of
these things are, long term."
JAMA Neurology, online Jan. 27, 2014.
[© 2014 Thomson Reuters. All rights
Copyright 2014 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.