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Patients suffering from Alzheimer's disease have comparatively higher levels of DDE - the long-lasting metabolite of the pesticide DDT in the blood than healthy people, according to a new study. 

Researchers considered 86 Alzheimer's patients and 79 other healthy elder people. They found that DDE levels were four times higher in serum samples collected from Alzheimer's patients than from other healthy people. Notably, DDE levels in the highest third of the range in the research increased patient's risk of disease by four times. 

"This is one of the first studies identifying a strong environmental risk factor for Alzheimer's disease," said co-author Allan Levey, MD, PhD, director of Emory's Alzheimer's Disease Research Center and chair of neurology at Emory University School of Medicine, in a press release. "The magnitude of the effect is strikingly large -- it is comparable in size to the most common genetic risk factor for late-onset Alzheimer's."

In the research a plausible mechanism by which DDE and DDT have Alzheimer's-related effects on the brain, was also identified. 

In the United State, DDT (dichlorodiphenyltrichloroethane) was being used extensively in agriculture and mosquito control. The use of DDT was later banned in 1972. 

"Measurement of serum DDE levels accompanied by ApoE genotyping might be a useful clinical measure to identify individuals who may be at increased risk for Alzheimer's," the authors wrote.

"An important next step will be to extend these studies to additional subjects and replicate the findings in independent laboratories," Levey added. "The potentially huge public health impact of identifying an avoidable cause of Alzheimer's disease warrants more study - urgently."

Nevertheless, the study also suggested that DDE levels were not solely responsible for someone getting Alzheimer's.

The findings are published in the journal JAMA Neurology.