Duke U. researchers have come one step closer to unraveling the mystery surrounding the development of Alzheimer’s disease.

A recent study found a link between repeated exposure to pesticides and the onset of Alzheimer’s. Kathleen Hayden, assistant professor of medical psychology, analyzed data from the Cache County Study of Memory Health and Aging.

Duke researchers have come one step closer to unraveling the mystery surrounding the development of Alzheimer’s disease.

A recent study found a link between repeated exposure to pesticides and the onset of Alzheimer’s. Kathleen Hayden, assistant professor of medical psychology, analyzed data from the Cache County Study of Memory Health and Aging. The data draws from individuals over the age of 65 in one of Utah’s most agricultural counties, taking into account their occupational exposure to pesticides and future changes in cognitive health.

The study focused on those individuals with significant exposure to pesticides, rather than mild exposure in a residential setting.

“I don’t think this study has any implications for the average person other than I might tell my mom to follow the instructions on a bottle of pesticide—I wouldn’t tell her not to use it,” Hayden said. “This wasn’t made to make my mom be afraid to go out into the garden.”

In an occupational setting, Hayden noted the importance of having proper safety equipment and using it correctly.

Most of the individuals’ pesticide exposure was from organophosphate and organochlorine, two compounds commonly used in pesticides. These compounds are known to impact the nervous system by affecting levels of acetylcholine in the brain, a neurotransmitter involved in cellular communication. Organochlorine was even temporarily banned due to concerns about its neurotoxic effects in 1972. 2,4-dichlorophenoxyacetic acid, an organochlorine, is a component of Agent Orange—the common name for the toxic substance used during the Vietnam War for chemical warfare. Researchers are currently analyzing the effects of this compound on veterans of the war.

Other effects of pesticide exposure

The study at Duke is just one of the many analyses taking place worldwide of the long-term effects of commonly used pesticides.

One such study, led by Marc Weisskopf, assistant professor of environmental and occupational epidemiology at the Harvard School of Public Health, found that individuals exposed to pesticides had a 70 percent higher incidence of Parkinson’s disease than those not exposed.

This study is particularly significant because it used a prospective analysis, meaning that its participants were selected before anyone had already developed the disease, Weiskopf said. Otherwise, the perception that pesticides may have led to their condition can result in a bias when subjects are asked to recall their exposure.

Most studies compare exposure of healthy individuals with those with Parkinson’s, causing them to be more susceptible to the aforementioned bias, he added.

The prospective analysis lends greater strength to a possible link between pesticides and Parkinson’s disease, though the study did not identify the dangers of pesticide exposure in an occupational versus residential setting or a specific compound in pesticides leading to Parkinson’s.

Pesticides most likely affect the onset of Parkinson’s by causing cell death and protein accumulation, a characteristic symptom of the disease, Weisskopf said.

Beyond Parkinson’s, a recent study by a team of researchers—Steven Mlynarek, Youn Shim and Edwin van Wijngaarden­—has discovered a link between prenatal exposure to pesticides and the development of brain cancer in children.

Like the previous studies, the research does not establish a conclusive relationship between these two factors. It does, however, emphasize the need to exercise caution when using pesticides.

“Pesticides are commonly used substances at home and at work,” van Wijngaarden wrote in an e-mail. “It is always a good idea to limit exposures as much as you can—especially [for pregnant women] during a time window of important brain development in the child.” Van Wijngaarden is chief of the division of epidemiology and associate professor in the departments of community and preventive medicine, environmental medicine and dentistry at the University of Rochester.

Prenatal exposure is likely to be much more damaging than exposure after birth, he added.