Research on pesticides’ impact on health has uncovered numerous associations between these toxins and various physical, mental, and emotional disorders. But what do we know about pesticides and Alzheimer’s disease?
As it turns out, not a lot. But that is changing slowly, and it’s about time. Pesticide use (which includes insecticides, fungicides, herbicides, and other chemicals) in the United States in 2006 and 2007 exceeded 1.1 billion pounds per year. That use accounts for 22 percent of the pesticides used in the entire world. The 1.1 billion pound figure holds true (with some years exceeding 1.2 billion) since 1988. Exposure can come from treated fruits and vegetables as well as environments in which the poisons are used, such as fields, gardens, parks, and lawns, as well as facilities in which they are manufactured.
Pesticides and Alzheimer’s disease
A recent review in Frontiers in Cellular Neuroscience noted there is some evidence in animal studies that pesticides can interrupt tau function. Tau proteins are substances found in nerve cells and which, when they become damaged, have been associated with the development of Alzheimer’s disease.
The research in question found that pyethroid and carbamate, two commonly used insecticides, resulted in the death of neurons and dysfunction in memory and learning in rats. But there are human studies as well.
In France, a team evaluated the association between lifelong exposure to pesticides and neurodegenerative disease in people aged 65 and older. The authors discovered a 2.4-fold increased risk of Alzheimer’s disease among the men who had had occupational exposure to the toxins but no significant association among the women.
In a 2014 study in JAMA Neurology, researchers compared the levels of DDE (a byproduct of DDT, or dichlorodiphenyltrichloroethane) in the blood of 86 adults with Alzheimer’s disease and 70 healthy controls. DDE levels in the individuals with Alzheimer’s were nearly four times greater than those in the controls. In addition, the high pesticide levels were associated with significantly worse performance on cognitive scores.
It should be noted that use of DDT has been banned in the United States since 1972, a ban that was triggered by Rachel Carson’s expose in “Silent Spring“
published in 1962. Yet DDT lingers in the soil and is still used in some foreign countries on fruit and vegetable crops. DDT also can be found in farmed fatty fish (e.g., salmon) and imported shellfish.
Another study focused on the effect of DDT. This time the authors found that the toxin increased levels of amyloid-beta, another protein believed to play a key role in the development of Alzheimer’s disease. This study was performed using human brain cells.
The commonly used herbicide known as paraquat was part of an experiment conducted in mice. Scientists discovered that the exposed animals showed a significant increase in amyloid-beta levels associated with damage in the cerebral cortex, resulting in impaired memory and learning.
Protecting against Alzheimer’s disease
For now, no one can say for sure that pesticides cause Alzheimer’s disease, but it appears they play a role in brain health. Reducing exposure to these chemicals is our best defense. That means choosing organically grown foods, thoroughly washing and/or peeling conventionally grown fruits and vegetables, using natural pesticides in our gardens and yards, eliminating use of farm raised fish and imported shellfish, and avoiding chemically treated areas.
You also can become involved in movements that are raising awareness of the dangers of pesticide use, such as Beyond Pesticides and the Pesticide Action Network. Actions taken now may help prevent development of this devastating disease in future generations.
Image: Tom Pratt