There has been considerable international study on the etiology of rising mental disorders, such as ADHD, in human populations. As glyphosate is the most commonly used herbicide in the world, we sought to test the hypothesis that glyphosate use in agriculture may be a contributing environmental factor to the increase in healthcare utilization among individuals with diagnosed ADHD.
State estimates for glyphosate use and nitrogen fertilizer use were obtained from the USGS. We queried the Healthcare Cost and Utilization Project net (HCUPNET) for state-level hospitalization discharge diagnosis data on all patients for all-listed ADHD cases from 2007 to 2010. The least squares dummy variable (LSDV) method and within the method using two-way fixed effects was used to elucidate the relationship between glyphosate use and all-listed ADHD hospital discharge diagnoses.
A 1-kg increase in glyphosate use in one year positively predicts state-level all-listed ADHD discharge diagnoses the following year (coefficient = 5.54E-08, p<.01). A study of the effects of urbanization on the relationship between glyphosate use and ADHD indicates that the relationship is marginally significantly positive in urban U.S. counties (p<.025). Furthermore, total glyphosate use is strongly associated with total farm use of nitrogen fertilizers from 1992 to 2006 (p<.001).
Glyphosate use is a significant predictor of state healthcare utilization for ADHD, with the effect concentrated in urban U.S. counties. We draw upon the econometric results to propose unique and exploratory mechanisms, borrowing principles from soil and atmospheric sciences, for how glyphosate-based herbicides may be contributing to the rise of ADHD in all populations.