(Beyond Pesticides, January 29, 2014) People with high levels of exposure to the banned insecticide DDT are four times more likely to have Alzheimer’s disease than people with low levels, according to a new study of patients in Georgia and Texas. The research is among the first to report a connection between Alzheimer’s disease, which is the world’s most common neurodegenerative disease, and chemicals in the environment.
The traces of the insecticide found in the study’s Alzheimer’s patients are comparable to the amounts found in most Americans today. Although it was banned more than 40 years ago in the U.S., DDT still persists in the environment worldwide and is still used today in developing countries for malaria abatement programs.
“Our findings suggest that genetically susceptible individuals with higher levels of DDT exposure may be more at risk,” said Jason Richardson, PhD, a Rutgers University researcher who led the study.
The case-control study consisting of existing samples from patients with Alzheimer’s disease and control participants from the Emory University Alzheimer’s Disease Research Center and the University of Texas Southwestern Medical School’s Alzheimer’s Disease Center measured serum levels of DDE in 79 control and 86 Alzheimer’s disease cases. Levels of DDE, a breakdown product of DDT, were 3.8 times higher in people who had the disease than in those who did not, according to the study, “Elevated Serum Pesticide Levels and Risk for Alzheimer Disease,” which was published in JAMA Neurology. Participants with the highest DDE levels were 4.18 times more likely to have Alzheimer’s than those with the lowest levels.
The researchers also found that people with both risk factors —high exposure and genetic susceptibility— “might have a more severe form of the disease,” Dr. Richardson said. Patients scored lower on a mental test if they had the highest DDE levels and a particular genetic variation associated with Alzheimer’s than if they had high DDE but did not have the genetic factor.
Seventy percent of the non-Alzheimer’s patients had detectable DDE in their blood, compared with 80 percent of the Alzheimer’s patients. Nationwide, 75 to 80 percent of all Americans tested have measurable levels in their blood. Because some of the Alzheimer’s patients had no DDE and some without the disease had high levels, the study “suggests that exposure to DDE may contribute to Alzheimer’s disease only in a subset of cases, perhaps those with genetic polymorphisms that render them more susceptible to DDT/DDE exposure,” the authors wrote.
More than 5 million people in the U.S. alone are living with Alzheimer’s, and cases are expected to triple over the next few decades. In recent decades, Alzheimer’s research has focused heavily on finding genetic causes of the disease. But fewer than half of cases can be blamed on genes alone, and researchers are now looking at how lifestyle and environmental factors may interact with genetic factors. According to Dr. Richardson, it is likely that any environmental exposures that may have contributed to the disease happened long before the patients had symptoms. Alzheimer’s is a slow-moving disease that develops over the course of decades. Because DDT takes many years to break down and leave the body, “results suggest that cumulative lifetime exposures may be important.”
The findings build upon previous research in which elevated levels of DDE were detected in the blood of 20 Alzheimer’s patients. While only a few studies have looked at potential environmental risk factors for Alzheimer’s, researchers have found links between pesticides and Parkinson’s, another degenerative brain disease. It is unclear whether there are periods early in life during which exposures to certain chemicals in the environment would be more likely to increase a person’s risk of eventually developing Alzheimer’s.
DDT already has been linked in other studies to reduced fertility, diabetes, and other health effects. But little has been known about its potential effects on the brain. A recent study reports that DDT affects multiple generations, ultimately contributing to obesity three generations down the line. However, the adverse impacts to humans ””including cancer, reproductive disease, neurological disease, developmental problems, diabetes and now Alzheimer’s disease”” paint a cautionary tale that long-banned pesticides continue to impact human health and the environment.
The Pesticide Induced Diseases Database (PIDD) keeps track of the most recent studies related to pesticide exposure. For more information on the multiple harms pesticides can cause, see Beyond Pesticides’ PIDD pages on Alzheimer’s, Parkinson’s, cancer, and other diseases.
Source: Environmental Health News
All unattributed positions and opinions in this piece are those of Beyond Pesticides