Pesticide Use and Incident Hypothyroidism in Pesticide Applicators in the Agricultural Health Study

Abstract

Background: Though evidence suggests that some pesticides may have thyroid-disrupting properties, prospective studies of associations between specific pesticides and incident thyroid disease are limited. Objective: We evaluated associations between use of specific pesticides and incident hypothyroidism in private pesticide applicators in the Agricultural Health Study (AHS). Methods: Self-reported incident hypothyroidism ( cases) was studied in relation to ever-use and intensity-weighted cumulative days of pesticide use at study enrollment. We estimated adjusted hazard ratios (HRs) and 95% confidence intervals (CI) using Cox proportional hazards models applied to 35,150 male and female applicators followed over 20 y. All models were stratified by state and education to meet proportional hazards assumptions ( for age x covariate interactions). Models of pesticides that did not meet proportional hazards assumptions were stratified by median attained age (62 y). Results: Hypothyroidism risk was significantly increased with ever- vs. never-use of four organochlorine insecticides (aldrin, heptachlor, and lindane among participants with attained age ; chlordane in all participants), four organophosphate insecticides (coumaphos in those ; diazinon, dichlorvos, and malathion in all participants) and three herbicides (dicamba, glyphosate, and 2,4-D in all participants). HRs ranged from 1.21; 95% CI: 1.04, 1.41 (chlordane) to 1.54; 95% CI: 1.23, 19.4 (lindane in those ). Hypothyroidism risk was greatest among those with higher intensity-weighted lifetime days of using chlordane, lindane, coumaphos (over age 62), diazinon, permethrin, and 2,4-D. Conclusions: Our findings support associations between exposure to several pesticides and increased hypothyroidism risk. These findings are generally consistent with prior analyses of prevalent hypothyroidism in the AHS. https://doi.org/10.1289/EHP3194

Pesticides With Potential Thyroid Hormone-Disrupting Effects: A Review of Recent Data

“…A prospective cohort study of licensed pesticide applicators in North Carolina and Iowa with 35,150 male and female participants demonstrated that self-reported use of glyphosate was associated with increased risk of hypothyroidism (91). However, these findings are not consistent with results obtained from the same cohort study conducted by Goldner et al (49) and Lerro et al (92).…”

“…When considering adults, results are more contradictory with some studies reporting effects more in line with hyperthyroidism in men (84), aging women (85) and occupational workers (86), while others found that OCPs were related to clinical or subclinical hypothyroidism in women (87), elderly men (88), adolescents (89) and pesticide applicators (48,49,(90)(91)(92). Moreover, an analysis of data on several organochlorines acquired from the United-States cross-national survey NHANES 7 did not find an effect of p,p ′ -DDE on TT4 in adults due to inconsistent results in both sampling cycles (1999-2000 and 2000-2001), and associations with TSH were not significant (93).…”

A comprehensive analysis of the animal carcinogenicity data for glyphosate from chronic exposure rodent carcinogenicity studies

“…In humans, Samsel et al [95] hypothesized that glyphosate intake could interfere with selenium uptake, impacting thyroid hormone synthesis and increasing thyroid cancer risks. Using data from the Agricultural Health Study, Shrestha et al [96] saw an association between ever/never use by farmworkers of GBHs and hypothyroidism (OR = 1.28, 95% CI 1.07-1.52) and for the two lowest categories of intensity of use, but not the highest category.…”

Pesticide use and incident hyperthyroidism in farmers in the Agricultural Health Study

“…Recently, we reported elevated risk of hypothyroidism in farmers exposed to several organochlorine and organophosphate insecticides and phenoxy herbicides 7. Here, we report associations between pesticide use and incident hyperthyroidism in AHS farmers.…”

“…This observation offers some reason to believe that the failure to confirm the hyperthyroidism diagnoses was structural and not due to misreporting by participants. Furthermore, if those who reported hyperthyroidism actually had hypothyroidism, we would have expected results for hyperthyroidism in these farmers to be similar to those for hypothyroidism,7 which was not the case.…”