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Original research
Occupational pesticide use and self-reported olfactory impairment in US farmers
  1. Srishti Shrestha1,
  2. David M Umbach2,
  3. Laura E Beane Freeman3,
  4. Stella Koutros3,
  5. Michael C R Alavanja4,
  6. Aaron Blair3,
  7. Honglei Chen5,
  8. Dale P Sandler1
  1. 1 Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
  2. 2 Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
  3. 3 Occupational and Environmental Epidemiology Branch, National Cancer Institute, Rockville, Maryland, USA
  4. 4 Formerly of Occupational and Environmental Epidemiology Branch, National Cancer Institute, Rockville, Maryland, USA
  5. 5 Department of Epidemiology and Biostatistics, College of Human Medicine, Michigan State University, East Lansing, Michigan, USA
  1. Correspondence to Dr Dale P Sandler, Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA; sandler{at}


Objectives Pesticide exposure may impair human olfaction, but empirical evidence is limited. We examined associations between occupational use of 50 specific pesticides and olfactory impairment, both self-reported, among 20 409 participants in the Agricultural Health Study, a prospective cohort of pesticide applicators (mostly farmers, 97% male).

Methods We used logistic regression models to estimate odds ratios (OR) and 95% confidence intervals (CI) for associations between pesticide use at enrolment (1993–1997) and olfactory impairment reported two decades later (2013–2016), adjusting for baseline covariates.

Results About 10% of participants reported olfactory impairment. The overall cumulative days of any pesticide use at enrolment were associated with a higher odds of reporting olfactory impairment (OR (highest vs lowest quartile): 1.17 (95% CI: 1.02 to 1.34), p-trend = 0.003). In the analyses of 50 specific pesticides, ever-use of 20 pesticides showed modest associations with olfactory impairment, with ORs ranging from 1.11 to 1.33. Of these, higher lifetime days of use of 12 pesticides were associated with higher odds of olfactory impairment compared with never use (p-trend ≤ 0.05), including two organochlorine insecticides (dichlorodiphenyltrichloroethane and lindane), two organophosphate insecticides (diazinon and malathion), permethrin, the fungicide captan and six herbicides (glyphosate, petroleum distillates, 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid and metribuzin), although many of these did not exhibit clear, monotonic exposure-response patterns.

Conclusion Overall, we found relatively broad associations between pesticides and olfactory impairment, involving many individual pesticides and covering several chemical classes, suggesting that pesticides could affect olfaction through multiple pathways. Future epidemiological studies with objective measurement of olfaction are required to confirm these findings.

  • pesticides
  • epidemiology
  • neurobehavioural effects

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  • HC and DPS are joint senior authors.

  • HC and DPS contributed equally.

  • Contributors SS, HC and DPS conceptualised this analysis. SS led the data analysis and prepared the first draft of the manuscript, which was overseen by HC and DPS. DMU provided statistical help. LEBF and DPS were involved in data acquisition and study management. All the authors were involved in data interpretation, reviewing and editing the manuscript, and providing final manuscript approval. All contributors meet the criteria for authorship.

  • Funding This work was supported by the Intramural Research Program of the National Institute of Health, National Institute of Environmental Health Sciences (Z01-ES-049030) and National Cancer Institute (Z01-CP-010119). Dr. Chen is supported by the Michigan State University (GE100455), the National Institute of Environmental Health Sciences (R01ES029227), the Parkinson’s Foundation (PF-IMP-1825) and the Office of the Assistant Secretary of Defense for Health Affairs, through the Parkinson’s Research Program (W81XWH-17-1-0536). Opinions, interpretations, conclusions and recommendations are those of the author and are not necessarily endorsed by the Department of Defense.

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Ethics approval The study was approved by the Institutional review boards of the National Institute of Environmental Health Sciences (North Carolina, protocol number 11-E-N196) and the National Cancer Institute (Maryland, protocol number OH93-NC-N013).

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement Requests for data, including the data used in this manuscript, are welcome as described on the Study Website ( Data requests may be made directly at; registration is required. The Agricultural Health Study is an ongoing prospective study. The data sharing policy was developed to protect the privacy of study participants and is consistent with study informed consent documents as approved by the NIH Institutional Review Board. Dr Dale Sandler is the NIEHS Principal Investigator of the Agricultural Health Study and is responsible for ensuring participant safety and privacy.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.