A study comparing blood serum levels of the DDT metabolite, DDE, in 86 patients with Alzheimer's disease (average age 74) and 79 controls (average age 70), has found that levels of DDE were 3.8 times higher in 74 of the 86 Alzheimer’s patients (86%). Having the Alzheimer’s gene, APOe4, plus high levels of the pesticide, produced more severe cognitive impairment.
Brain cell studies found that DDE increased production of the amyloid precursor protein (APP).
DDT was banned in the U.S. in 1972, but is still used elsewhere. It also takes a long time to break down in the environment. DDE was found in 75-80% of blood samples collected from the Centers for Disease Control and Prevention for a national health and nutrition survey.
 . ELevated serum pesticide levels and risk for alzheimer disease. JAMA Neurology [Internet]. 2014 ;71(3):284 - 290. Available from: http://dx.doi.org/10.1001/jamaneurol.2013.6030