Researchers at Rutgers University found that exposure to the synthetic insecticide DDT (dichloro-diphenyl-trichloroethane) may increase the risk and severity of Alzheimer’s disease, particularly in people over the age of 60. A new study, published in JAMA Neurology, discusses how levels of the pesticide were higher in the blood of late-onset Alzheimer’s patients compared to patients without the disease.

DDT was introduced during WWII for controlling insects on crops and livestock as well as to combat insect-borne diseases such as malaria.

The once widely-used DDT has been banned in the United States since 1972 due to its adverse environmental impacts, such as harm to wildlife, and potential risks to human health. It is currently classified as a probable human carcinogen in the US and elsewhere, though it is still used in some countries. The World Health Organization (WHO) still recommends using DDT to control malaria.

Researchers found that 74 of 86 Alzheimer’s patients involved in the study had 3.8 times the level of DDE – the chemical compound that remains after DDT breaks down – that healthy patients had, BBC News reports. However, some healthy people had high levels of DDE and some with Alzheimer’s had low levels.

Although levels of DDT have decreased significantly in the US since 1972, the toxic insecticide is still present in 75 to 80 percent of blood samples collected from the Centers for Disease Control and Prevention’s national health and nutrition survey, according to a Rutgers research news release. This is likely due to the fact that the chemical can take decades to break down in the environment. It is also possible that US residents are exposed to DDT through imported fruits, vegetables, or grains.

Scientists believe that Alzheimer’s may be a result of a combination of genetic, environmental, and lifestyle factors. The recent study finds that patients with a certain gene (ApoE4), which greatly increases the risk of developing Alzheimer’s, as well as high blood levels of DDE suffered even more sever cognitive impairment then did patients without the gene.

They also found that DDT and DDE increased the amount of a certain protein associated with the development of amyloid plaques in the brain, a hallmark of Alzheimer’s disease, which contribute to brain cell death. The research is important because it suggests DDT and DDE may directly contribute to plaque development.

Although more research is needed, Jason Richardson, an associate professor in the Department of Environmental and Occupational Medicine at Rutgers Robert Wood Johnson Medical School says the results of the latest study “demonstrate that more attention should be focused on potential environmental contributors and their interaction with genetic susceptibility.”

“Our data may help identify those that are at risk for Alzheimer’s disease and could potentially lead to earlier diagnosis and an improved outcome,” he adds.

Alisha is a writer and researcher with Ring of Fire. You can follow her on Twitter @childoftheearth.