Long-Term Pesticide Use and Risk of Dementia in the Agricultural Health Study of Memory in Aging

Background

Pesticide use has been associated with increased risk of dementia in some, but not all studies; however, little is known about the long-term impact of specific pesticides on dementia risk. We investigated the association between 41 pesticides from 8 pesticides classes, and dementia among pesticide applicators from Iowa and North Carolina who participated in the Agricultural Health Study of Memory in Aging (AHS-MA).

Methods

The study sample included AHS-MA participants aged 70+ who completed a telephone cognitive screening interview from 2015-2018. Those with suspected dementia based on the telephone interview then completed a comprehensive in-person dementia evaluation. Dementia diagnoses were assigned by an adjudication team. Details about pesticide ever-lifetime-use were collected from 1993–1997 from licensed pesticide applicators (mostly farmers), 18–25 years before the telephone interview. Generalized estimating equations were used to examine the log-odds ratio between pesticide use and dementia, after accounting for inverse probability weights, age, education, and state. For screening purposes, we report associations with p≤0.01.

Results

Participants (113 with dementia; 81 with clinically defined Alzheimer’s disease (AD); 2084 without dementia) had a mean age of 80.3 (SD 5.4); 96% were males; 98% White; 59% from Iowa; and 12.8 years mean education (SD 2.5). In preliminary analyses we observed associations between dementia and fungicides in general (OR 3.0, 95% CI 1.4-6.8), and the specific pesticides Benomyl (OR 3.4, 95% CI 1.3-9.1), DDT (OR 2.4, 95% CI 1.2-4.7) and 2,4,5-T (OR 2.5, 95% CI 1.2-5.3). Results were similar for AD.

Conclusions

Overall, few pesticides were associated with increased risk of dementia or AD. Yet, clearly the risk is not uniform across all pesticides. It is notable that two of the pesticides (DDT and 2,4,5-T) associated with increased risk of dementia were banned from use beginning in the 1970’s. Both DDT and contaminants of 2,4,5-T are widespread persistent organic pollutants with long-half lives in the body. These findings raise questions about whether the association between these banned pesticides and dementia is due to prior exposure or residuals in the environment. We are currently investigating whether the serum level of DDT and its metabolite DDE are associated with higher risk of dementia.

The full study is available in Alzheimer’s & Decision.