Occupational pesticide exposure and subclinical hypothyroidism in the Agricultural Health Study

Abstract

Introduction: Occupational use of specific pesticides affects thyroid function in humans but epidemiologic studies of thyroid disease are limited. Methods: We evaluated occupational pesticide exposure and subclinical hypothyroidism among 679 male pesticide applicators in the Agricultural Health Study cohort (Iowa, North Carolina, USA) who participated in the Biomarkers of Exposure and Effect in Agriculture study. Self-reported lifetime use of 50 pesticides was obtained at enrollment (1993-1997). Pesticide metrics incorporated total days of use adjusted for personal protection (intensity-weighted lifetime days: none, low ≤median, high >median). Blood samples were collected in 2010-2013 and were measured for thyroid- stimulating hormone (TSH) using the Millipore human pituitary panel multiplexing kit. For 40 pesticides with >5 exposed cases, we used multivariate logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for subclinical hypothyroidism (TSH>4.5 mU/L) compared to normal TSH (0.4-<4.5mU/L), adjusting for confounders. Results: Prevalence of subclinical hypothyroidism was 18% (vs. <5% in men of similar age in a national sample). Applicators exposed to the herbicides cyanazine (ORHigh:2.4, CI 1.4‒4.1) and EPTC (ORHigh:2.0, CI 1.0‒3.9), and insecticides diazinon (ORHigh: 2.5, CI 1.1‒5.8) and aldrin (ORHigh:3.0, CI 1.3‒6.7) had increased prevalence of subclinical hypothyroidism with positive exposure-response trends (ptrend<0.05). No other herbicides, insecticides, fungicides, or fumigants showed significant trends. Conclusions: In this comprehensive evaluation of occupational pesticide exposure, several pesticides were positively associated with subclinical hypothyroidism. Our results for diazinon are consistent with those for self-reported clinical hypothyroidism among pesticide applicators in the cohort, supporting a role for specific pesticide exposures in hypothyroidism.