People with high levels of the pesticide DDT in their blood may be at increased risk of Alzheimer's disease, a study from the US suggests.
Published in the JAMA Neurology journal, the research was led by a teams at the Rutgers and Emory universities in New Jersey and is the first to look at the possible connection between DDT and cognitive decline.
DDT is currently banned in the UK, but was once widely used to protect crops in the years immediately after World War II. In some countries, it is still used as a way of fighting malaria.
Once in the body, DDT is broken down into a chemical compound known as dichlorodiphenyldichloroethylene (DDE).
Some 86 people with Alzheimer's and 79 without the condition were recruited to take part in the study, with their blood tested for levels of DDE.
And the results showed that on average those with the illness had greater amounts of the compound in their bodies.
Further tests on brain cells found that DDT and DDE caused an increase in the amount of amyloid precursor protein building up, which increased production of amyloid plaques and makes Alzheimer's more likely.
Professor Allan Levey, director of the Alzheimer's Disease Research Centre at Emory University, said: "This is one of the first studies identifying a strong environmental risk factor for Alzheimer's disease.
"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."
However, Dr Simon Ridley, head of research at the charity Alzheimer's Research UK, said the study cannot be seen as a direct link between pesticides and Alzheimer's and called for further research to be conducted.
At present, an estimated 820,000 are currently living with some form of dementia in the UK and the figure is set to rise above the one million mark by 2021 unless a significant breakthrough in research is made.
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