August 13, 2014
Exposure to the pesticide DDT may raise the risk of Alzheimer’s disease years later, a new study suggests. The finding raises concerns about the effects of environmental toxins on the brain and how they may affect the onset or severity of Alzheimer’s disease.
Though DDT has been banned in the United States since 1972, it was widely used beginning in the 1940s and residues can remain in the environment for decades. Many older adults were directly exposed to the chemical when young. DDT is also still used in many countries around the world for insect control in crops and livestock and to limit the spread of diseases like malaria, and it may be ingested in imported fruits, vegetables, fish and other foods.
For the study, scientists looked at DDE, the chemical that remains after DDT is broken down. They studied blood samples from 86 elderly men and women – average age 74 – with Alzheimer’s disease, and compared them with 79 of their healthy peers.
The researchers, from Rutgers University, Emory University and the University of Texas Southwestern Medical Center, found that 80 percent of those with Alzheimer’s had DDE residues in their blood. In comparison, only 70 percent of those without Alzheimer’s had DDE in their bodies. DDE levels in those with Alzheimer’s were, on average, almost four times higher than in those without the disease. The findings appeared in JAMA Neurology.
In the study, those who carried the APOE-E4 gene, which raises the risk of developing Alzheimer’s in old age, appeared to be particularly vulnerable to the possible effects of DDT. Those APOE-E4 carriers who had high levels of DDE in their systems showed greater declines in thinking and memory skills than similar patients without the gene. It is possible that DDT exposure may nudge people toward Alzheimer’s in those who are already genetically predisposed, the authors say.
In an editorial that accompanied the study, doctors noted that the results are preliminary and need further corroboration. But they say that it raises intriguing questions about the role of environmental factors in Alzheimer’s onset.
They point out that identical twins, for example, who share the same genes, typically do not get Alzheimer’s at the same rate or at the same age of onset. So factors besides genes likely play a role. Head injuries are a well known risk factor for Alzheimer’s, and other conditions like high cholesterol, diabetes, high blood pressure and obesity are linked to increased risk. While a study like this one shows a correlation between DDT exposure and Alzheimer’s, it cannot prove that pesticides actually cause the disease.
Pesticides have been strongly tied to other brain disorders, including Parkinson’s disease. The authors note that more research must be done to understand better the potential link between pesticides and Alzheimer’s.
“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,” said the study leader, Dr. Jason Richardson, of the Department of Environmental and Occupational Medicine at Robert Wood Johnson Medical School at Rutgers. “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.”
Sources: Jason R. Richardson, PhD; Ananya Roy, ScD; Stuart L. Shalat, ScD; et al: “Elevated Serum Pesticide Levels and Risk for Alzheimer’s Disease.” JAMA Neurology, online January 29, 2014.
Steven T. DeKosky, MD, Sam Gandy, MD, PhD: “Environmental Exposures and the Risk for Alzheimer DiseaseCan We Identify the Smoking Guns?” (editorial). JAMA Neurology, online January 29, 2014.