Exposure to a pesticide banned in 1986 might have increased the risk of developing Alzheimer's disease, scientists have warned.
People who were found to have the highest levels of DDT in their system were four times more likely to have the degenerative disease.
DDT (dichlorodiphenyltrichloroethane) was banned as a pesticide worldwide under the Stockholm Convention in 2001 after it was discovered to be dangerous to wildlife and the environment. But researchers found it was still present in bodily tissue decades later, broken down into the chemical compound DDE.
A study found that people suffering from Alzheimer's disease had more than four times the level of DDE in their bloodstreams compared with those who did not have the disease.
The researchers said the preliminary findings suggest the pesticide may contribute to the disease alongside other genetic risk factors.
"This is one of the first studies identifying a strong environmental risk factor for Alzheimer's disease," said Dr Allan Levey, a co-author. "The magnitude of the effect is strikingly large."
The team compared a group of 86 Alzheimer's patients with 79 people who did not have the disease.
They found levels of DDE were four times higher in 74 of the Alzheimer's patients than those without the disease.
Furthermore, patients who were carrying a gene that increases the risk of Alzheimer's had even more severe cognitive impairment if they had been exposed to high levels of DDE.
The pesticide was used from the 1940s onwards until it was banned.
The researchers, writing in 'JAMA Neurology', suggest that doctors should test for DDE as a predictor of the disease.
Carol Brayne, a professor at Cambridge University, said the research had produced a "very interesting result" but it was too early to come to a conclusion about a link between DDT exposure and Alzheimer's. (© Daily Telegraph, London)