Pesticide DDT Linked to Heightened Alzheimer’s Risk

The pesticide DDT, banned in the U.S. because of its toxic effects on wildlife and potential to harm human health, may raise the risk for Alzheimer’s disease, according to the first study linking the chemical to the brain-ravaging illness.

People with Alzheimer’s disease had about four times the level of a DDT byproduct in their blood compared with those who didn’t have the dementia, according to the research published yesterday in the journal JAMA Neurology.

DDT, outlawed in the U.S. in 1972, is still found in blood samples because it can take decades for chemicals to break down. The pesticide is used in other countries, and U.S. residents can ingest it by eating fruits, vegetables and grains that are grown in those areas, researchers said. The study points to the need for more analysis about how environmental factors may interact with genes to boost Alzheimer’s risk, said Jason Richardson, the lead study author.

“We really need more attention on the role of environment and the interaction of your genes and environment for complex diseases such as Alzheimer’s,” Richardson, an associate professor in the Department of Environmental and Occupational Medicine at the Robert Wood Johnson Medical School at Rutgers University in Piscataway, New Jersey, said in a telephone interview. “The prevailing thought has always been it’s a genetic disease. Unfortunately that hasn’t panned out.”

Protein Interactions

Just how DDT and its byproduct, DDE, are linked to Alzheimer’s disease remains unclear. The pesticide may affect levels of proteins in the brain that are associated with the plaque that leads to the disease, Richardson said. More studies are needed to better understand this interaction, he said.

Researchers analyzed blood samples of 86 people who had been diagnosed with Alzheimer’s and 79 patients without the condition. They also analyzed brain samples of 11 Alzheimer’s patients who had died and had previously provided blood samples.

They found DDE in 80 percent of those with Alzheimer’s and 70 percent of those without the disease. Those with Alzheimer’s had DDE levels 3.8 times higher on average. The study also showed that those with the Alzheimer’s gene ApoE4 and high levels of DDE scored the lowest on cognition tests.

“This study demonstrates that there are additional contributors to Alzheimer’s disease that must be examined and that may help identify those at risk of developing Alzheimer’s,” Richardson said in a statement. “It is important because when it comes to diagnosing and treating this and other neurodegenerative diseases, the earlier someone is diagnosed, the more options there may be available.”

No Cure

More than 5 million people in the U.S. have Alzheimer’s, a number projected to triple by 2050, according to the Alzheimer’s Association. There is no treatment for the disease, the most common form of dementia. The only drugs approved for the condition ease symptoms for a few months while the disease continues to worsen.

Steven DeKosky, a professor of neurology at the University of Virginia, wrote in an accompanying editorial that today’s study provides a “wake-up call” to look at environmental factors for Alzheimer’s disease and points researchers toward pesticides as a first area to assess.

“We have spent so much time looking for the genetic underpinnings of the disease. Now it’s time to start looking harder at the environment,” he said in a telephone interview. “We are exploring a lot of ways that the environment may predispose us to or protect us from neurodegenerative diseases later in life. This is a new clue that we will chase down.”

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