A study published this week in the medical journal JAMA Neurology has suggested there could be a link between exposure to infamous banned pesticide DDT and the development of Alzheimer's disease.

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Although researchers from Rutgers Univeristy's Robert Wood Johnson Medical School in New Jersey identified a potential relationship between Alzheimer's and the presence in participants' blood of DDE (a by-product formed when the body breaks down DDT), they said their findings are not conclusive.  However, they did identify how DDE could raise levels of certain proteins in nerve cells, which is associated with development of amyloid plaques, a key hallmark of the disease.

DDT was first used to control disease-carrying insects during World War Two, and was subsequently sold to commercial farmers for use in agricultural pest control.

In the study, DDE was detected in the blood of 70 percent of a control group and 80 percent of Alzheimer's patients. DDE levels in blood were associated with increased risk of developing Alzheimer's. On average, those suffering from the disease had DDE levels in their blood 3.8 times higher than members of the control group.

The researchers estimated that presence of DDE in patients' blood was mostly either the result of exposure earlier in the participants' life (the chemical has a long half-life), the residual presence of the chemical in soil and water in the U.S., where DDT was banned in 1972, or continued exposure through food imported from countries where DDT is still used.

Although DDT is no longer permitted for use as a pesticide, evidence suggests the chemical is still being supplied illegally to farmers in India and East Africa, where it is used on fruit, vegetable and cereal crops, as well as coffee.

Agricultural use of DDT was banned in many European states in the 1960s and '70s, starting with Hungary. However, the UK failed to introduce a ban until 1984. Other uses of DDT were outlawed in the EU in 1986, as part of a raft of measures taken between the mid-'80s and early '90s to outlaw a number of chemicals – mainly persistent organochlorine compounds – seen to cause harm, even when used to label instructions.

DDT and its legacy have been extremely controversial. The chemical was implicated in effects on wildlife following the publication of Rachel Carson's seminal work Silent Spring, which helped kickstart the environmental movement in the 1960s. Although vocal critics of bans and restrictions on DDT often point to its use in combating malaria in the Southern Hemisphere, views were, and still are strongly divided on the issue, and growing resistance to the chemical in mosquito populations – thought to be linked to its overuse in agriculture –was noted as early as the mid-1950s.

Alzheimer's is already the most common neurodegenerative disease in the world and the number of cases is expected to increase. Risk factors for contracting late-onset Alzheimer's are not yet fully understood, though the JAMA researchers said a genetic predisposition as well as lifestyle and environmental factors are thought to contribute.

Professor Jason Richardson, one of the study's authors commented, "I think these results demonstrate that more attention should be focused on potential environmental contributors [to Alzheimer's development] 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."