Exposure to the banned pesticide DDT could be an important risk factor in the development of Alzheimer's disease (AD), suggest findings of a study published in JAMA Neurology.

DDT has been outlawed in many countries for over 30 years (aside from indoor spraying to combat malaria) because of its potentially detrimental impact on wildlife, but the chemical has a very long half-life of up to 10 years.

Researchers from Rutgers University and Emory University analysed serum levels of 79 healthy control participants and 86 diagnosed with AD, and found that levels of DDE, the metabolite of DDT, were nearly four times higher in patients diagnosed with the condition.

Also, the relative (not actual) risk of developing AD for those with the highest levels of DDT exposure was found to be four times higher.

However, the relationship between DDT exposure and AD is not clear cut, as not all participants with high serum levels of DDE developed the condition.

Genetic factors

The researchers believe that carriers of a mutant gene called APOE4 may be more susceptible to the effects of DDE, which could spur the development of beta amyloid plaques in the brain linked with the disease.

Other experts have also cautioned against drawing definite conclusions from the study.

Simon Ridley, Head of Research at Alzheimer’s Research UK said: "We can’t conclude from these findings that pesticide exposure causes Alzheimer’s, and much more research would be needed to confirm whether this particular pesticide may contribute to the disease".

Nevertheless, the researchers note that "identifying people who have elevated levels of DDE and carry an APOE4 allele may lead to early identification of some cases of AD".