People with Alzheimer's disease may have higher levels of a chemical left behind by the pesticide DDT than healthy elderly people, a US study suggests.
America phased out DDT in 1972 but is still used elsewhere in the world and global health authorities consider it an important tool against malaria.
The report found that DDE, the long-lasting metabolite of DDT, was nearly four times higher in Alzheimer's patients than in peers without the disease.
Having high DDE levels was also linked to a fourfold increase in the risk of Alzheimer's.
The study, which was published in the Journal of the American Medical Association Neurology, compared 86 Alzheimer's patients to 79 healthy people of advanced age.
They came from the US states of Texas and Georgia, and their average age was 74.
Outside experts cautioned that its sample size was small and more research was needed.
The differences in DDE levels were seen in the Texas sample, but not in Georgia, noted an accompanying editorial by doctors at the University of Pennsylvania and the University of Virginia.
The editorial writers, Steven DeKosky and Sam Gandy, noted that the research should be considered "preliminary until there is independent confirmation in other populations".