Exposure to the pesticide DDT has been linked to Alzheimer's disease by a team of researchers working in Dallas and Atlanta. According to the researchers, study participants with Alzheimer's disease had blood levels of DDE (a metabolite of DDT) four times as high as participants without Alzheimer's. Dr. Jason Richardson, from Robert Wood Johnson Medical School, notes that although the United States banned the use of DDT in 1972, it is still used in other parts of the world, including those that supply produce to the United States. Beyond current exposure through food and travel, Dr. Richardson adds, DDT is a persistent environmental pollutant that remains in soil for years.
Recent research has pointed to a link between DDT and chronic illnesses of all types, including Parkinson's disease and obesity. Steven DeKosky and Sam Gandy, two doctors writing an opinion piece in JAMA, note that although many genes linked to Alzheimer's have been identified, they explain only a small portion of the risk for the disease. "Despite the advanced in genetics and diagnostic markers," the doctors note, "the variability in risk and the limited power of allelic risk candidates [...] have led increasingly to the conclusion that environmental factors and toxic exposures must also contribute significantly to the risk for developing late-onset Alzheimer's disease." [Emphasis added.]
This finding is significant both in the potential for its ability to explain the incidence of Alzheimer's disease and in its value as a warning regarding the pesticides in common use today. Glyphosate, commonly formulated with other chemicals and sold as Roundup, has been linked to toxic effects on human cells, genotoxic effects on fish, immune system impairment in fish, and reproductive impairment in fish. Atrazine, a pesticide commonly used on strawberries and other produce in the United States, has documented deleterious effects on human health.
Economists describe the concept of a "negative externality" this way: "A negative externality occurs when an individual or firm making a decision does not have to pay the full cost of the decision. If a good has a negative externality, then the cost to society is greater than the cost the consumer is paying for it." With the cost of dementia estimated at 109 billion dollars in 2010 and projected to double by 2040, it seems prudent for scientists to determine the factors that increase the burden of neurological disease, and for public health officials to work to ameliorate this burden or charge the appropriate parties the ever-increasing cost.