DDT and Alzheimer's disease: Is there a link?
Researchers may have uncovered another risk factor for why people develop Alzheimer's disease from exposure to the banned pesticide DDT.
In a small, case controlled study, scientists measured levels of a by-product of DDT (DDE) in the blood of 86 people with Alzheimer's disease, comparing the results to 79 controls.
Jason R. Richardson, PhD, of Rutgers Robert Wood Johnson Medical School in Piscataway, N.J., and colleagues who carried out the study discovered DDT exposure and levels of the by-product called DDE was associated with quadruple the risk of Alzheimer's disease, compared to controls.
The finding that is published in JAMA Neurology suggests the chemical that was banned in 1972 promotes the formation of chemicals that are precursors to beta-amyloid plaque found in the brain's of Alzheimer's disease patients.
How could DDT cause Alzheimer's decades later?
The pesticide lingers in the environment. It is also used in other parts of the world, meaning imported foods could still contain DDT.
Pesticide exposure is associated with a variety of other neurological disorders including Parkinson's disease. The finding from Richardson and colleagues doesn't prove DDT exposure ups the risk of Alzheimer's disease, but it opens the door for more investigation to understand the harm the chemicals might cause for human health.
What we know about Alzheimer's risk to date:
- There is a strong genetic component
- Environmental factors are believed to contribute to dementia and Alzheimer's disease including head trauma and lifestyle factors such as exercise and diet
- Vascular disease from diabetes and blood vessel inflammation might contribute to Alzheimer's disease
- Symptoms develop late, after brain changes have already occurred
- Rates of Alzheimer' disease are increasing
What we know about DDT
- The pesticide was heavily used during World War II to kill mosquitoes and prevent malaria
- After 1945 it was used as an agricultural pesticide, exposing civilians
- DDT is more readily absorbed in fat and is taken up by the gastrointestinal tract
- Studies in monkeys showed it disrupts functioning of the central nervous system
- Low doses affect neurological development in mice
- It accumulates and remains in the soil and is not soluble in water
- DDT is not stored by plants to any great degree
Environmental triggers have been suspected for playing a role in other diseases too. Examples include autoimmune conditions that seem to affect vulnerable individuals. In this study, the researchers say it might be possible that some people are at higher risk for Alzheimer's because DDT may be metabolized more rapidly.
Richardson J, et al "Elevated serum pesticide levels and risk for Alzheimer disease" JAMA Neurol 2014; DOI: 10.1001/jamaneurol.2013.6030.
Agency for Toxic Substances and Diseases Registry (ATSDR)/US Public Health Service, Toxicological Profile for 4,4'-DDT, 4,4'-DDE, 4, 4'-DDD (Update). 1994. ATSDR. Atlanta, GA.
World Health Organization (WHO). 1989. Environmental health Criteria 83, DDT and its Derivatives--Environmental Effects. World Health Organization, Geneva
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