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NEW YORK (Reuters Health) - People who had been exposed to the pesticide DDT were more likely to have Alzheimer's disease than those with no traces of the chemical in their blood, researchers found in a new study.
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 Jersey.
"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.
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 Reuters Health.
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 pesticides.
"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."
(This story has been refiled to add "Rutgers" to Richardson's affiliation in paragraph 4)
SOURCE: bit.ly/1gkB2q7 JAMA Neurology, online January 27, 2014.