Pesticides and Alzheimer’s Disease

Celeste Chen, National Center for Health Research

Caution sign: Pesticide spraying in progress Proceed at own riskOver the next 40 years, the number of people in the world with Alzheimer’s Disease, the most common form of dementia, is expected to triple.[1]  Because Alzheimer’s strikes as people get older, the U.S. is expecting a big increase in this brain-wasting disease as baby boomers become seniors.

Pesticides, which kill insects by attacking their nervous systems, and herbicides, which wipe out some plants but not others, are increasingly being linked to diseases that attack our nervous systems and brains. Several studies have shown that individuals regularly exposed to pesticides and herbicides are more likely to develop Parkinson’s Disease (PD), which makes it difficult for people to control their movements and can cause emotional changes.[2] Now, there is reason to believe that pesticide exposure can also increase a person’s chances of developing Alzheimer’s Disease.[3]

A study published in 2014 in the prestigious medical journal JAMA showed a link between Alzheimer’s and DDT, an ingredient in many pesticides in the 1970s.[4]  Farmers and other agricultural workers who were exposed to high levels of DDT decades ago are much more likely to suffer from dementia, including Alzheimer’s, than are other people. DDT was banned in the U.S. in 1972, but people continue to come into contact with this dangerous pesticide by:

  • Buying imported foods from countries such as India, Spain, Mozambique, and Ethiopia where DDT or DDT-like pesticides are still in use.[5] [6]
  • Living in agricultural areas where DDT was once sprayed as a pesticide. Even though it has not been used for over 40 years in the US, DDT is still present in our soil because it takes decades for DDT to be broken down naturally.[7] [8]
  • Living near former industrial sites. In the 1970s, manufacturing plants dumped waste products containing DDT, which contaminated riverbeds and local waters. The Palo Alto Superfund site is one example of an area contaminated with DDT and other chemicals. Fish at these sites still contain DDT because DDT remains in the water for over 300 years.[9] [10]  
  • Chance.  When DDT breaks down, it produces DDE, another harmful chemical. Both DDT and DDE enter the air as they evaporate from contaminated water and soil. As a result, DDE and DDT are sometimes found far away from the source of DDT dump sites. DDE and DDT have even been found in such remote areas as the Arctic and Antarctica. As DDT and DDE evaporate, they are made safer by sunlight. Unfortunately, the process of evaporation also helps spread and deposit the chemicals to new places.[11]

DDT/DDE and Alzheimer’s

In the 2014 study on Alzheimer’s Disease and DDT, not all the individuals who had the disease had high levels of DDE (the chemical produced when the body breaks down DDT) in their blood. Moreover, some of the participants in the study who didn’t have Alzheimer’s also had detectable levels of DDE.

This tells us that DDT is only one possible cause of Alzheimer’s and dementia, and also suggests that some people are genetically more vulnerable to the harmful impact of DDT. For instance, individuals with the e4 version of the APOE gene (apolipoprotein) are more likely to have late-onset Alzheimer’s than people with e2 or e3 versions.[12]

The Alzheimer’s patients who scored worst on the reasoning and memory tests in the 2014 study were men and women who had both the APOE e4 gene and the highest levels of DDE in their blood. From these results, the scientists speculated that DDT/DDE may somehow interact with the APOE e4 gene to significantly increase a person’s risk of Alzheimer’s.

What the Study Doesn’t Tell Us

This 2014 study looked at organochlorides, which is only one type of chemicals found in pesticides. After DDT was banned, replacement pesticides were introduced but none of these were tested for safety.  Other types of chemicals used in pesticides, such as organophosphates, may also increase a person’s risk of developing Alzheimer’s. We simply don’t know yet.  There is some evidence that a popular alternative to DDT, malthion, may cause cancer.[13]  Malthion is an organophosphate. Children exposed to organophosphates have been found to have a higher risk of developing childhood cancer and having behavioral problems and decreased mental functioning.

Bottom Line

Though this study was limited to studying the effects of organochlorides (DDT), it is possible that other types of chemicals in pesticides will someday be linked to diseases like Parkinson’s and Alzheimer’s. What kills an insect or plant quickly, could—with enough exposure over time—harm your neurons, which are your brain’s building blocks.

Although DDT was banned more than 40 years ago, many of us are still exposed today though imported foods, through our own contaminated soil and water, or by eating fish that live in those waters.

In the U.S., prescription drugs have to be proven safe before they can be sold, but chemicals do not have to be proven safe before they can be sold.  It often takes many years of use before it becomes obvious how dangerous a chemical can be. When DDT was found to be dangerous, it was just replaced by other chemicals whose safety was unknown.  Some of those chemicals may be just as dangerous as DDT, and there is increasing evidence that they can harm human health.

Changing the laws of our country to require better safety studies could save lives and potentially decrease the risk of Alzheimer’s disease.  In the meantime, we can help make our home environments safer:

  1. Always cover exposed skin with long sleeves, socks, gloves and eyewear when applying pesticides and wash yourself thoroughly afterwards.
  2. Always rinse fruits and vegetables with water before eating them, and peel them if at all possible.
  3. When applying insecticides/pesticides indoors or outdoors, always follow the instructions on the label exactly, and keep children, toys, and pets away from the area until the insecticide or pesticide dries or for as long as instructed.

For more information on how to limit your exposure to pesticides, check out these safety guides:

  1. https://www.epa.gov/pesticides
  2. https://www.osha.gov/SLTC/youth/agriculture/chemicals.html

 

All articles are reviewed and approved by Dr, Diana Zuckerman and other senior staff.

 

  1. Richardson J, et al “Elevated serum pesticide levels and risk for Alzheimer disease” JAMA Neurol 2014; DOI: 10.1001/jamaneurol.2013.6030.
  2. Richardson JR, Shalat SL, Buckley B, et al. Elevated serum pesticide levels and risk of Parkinson disease. Archives of Neurology. 2009;66(7):870–875.
  3. Richardson J, et al “Elevated serum pesticide levels and risk for Alzheimer disease” JAMA Neurol 2014; DOI: 10.1001/jamaneurol.2013.6030.
  4. Richardson J, et al “Elevated serum pesticide levels and risk for Alzheimer disease” JAMA Neurol 2014; DOI: 10.1001/jamaneurol.2013.6030.
  5. Botella B, Crespo J, Rivas A, Cerrillo I,Olea-Serrano MF, Olea N. Exposure of women to organochlorine pesticides in Southern Spain. Environ Res. 2004;96(1):34-40.
  6. Abbott, Michele, and Ben Johns. April 2013. PMIIRS Country Programs: Comparative Cost Analysis, August 11, 2011 – December 31, 2012. Bethesda, MD: Africa Indoor Residual Spraying (AIRS) Project, Abt Associates Inc.
  7. K.M. Hayden, M.C. Norton, D. Darcey, T. Ostbye, P.P. Zandi, J.C. Breitner, K.A. Welsh-Bohmer. Occupational exposure to pesticides increases the risk of incident AD: the Cache County study. Neurology, 74 (2010), pp. 1524–1530.
  8. Toxicology Profile for 4,4′-DDT, 4,4′-DDE, 4,4′-DDD (Update); U. S. Department of Human Health & Human Services, Agency for Toxic Substances and Disease Registry, 1994.
  9. Water-related environmental fate of 129 priority pollutants. Callahan, M. A.; Slimak, M. W.; Gabel, N. W., Volume1. Washington, DC: United States Environmental Protection Agency, 1979. In: The Hazardous Substances Data Bank (HSDB) CD-ROM:U.S. National Library of Medicine; National Institutes of Health and Human Services: Bethesda, MD, 1998.
  10. “Triana/Tennessee River.” EPA. Environmental Protection Agency, n.d. Web. 05 Mar. 2014.
  11. Agency for Toxic Substances and Disease Registry (ATSDR). 2002. Toxicological profile for DDT, DDE, DDD. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
  12. Genetics Home Reference. “APOE.” – Apolipoprotein. Accessed Mar. 3, 2014. at http://ghr.nlm.nih.gov/gene/APOE
  13. Malathion: Revised human health risk assessment for the reregistration eligibility decision document (RED); EPA-HQOPP- 2004-0348-0057; U.S. Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, U.S. Government Printing Office: Washington, DC, 2006.