Abstract
There has been considerable international study on the etiology of rising mental disorders, such as attention-deficit hyperactivity disorder (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 rise of ADHD in human populations. State estimates for glyphosate use and nitrogen fertilizer use were obtained from the U.S. Geological Survey (USGS). We queried the Healthcare Cost and Utilization Project net (HCUPNET) for state-level hospitalization discharge data in all patients for all-listed ADHD from 2007 to 2010. We used rural-urban continuum codes from the USDA-Economic Research Service when exploring the effect of urbanization on the relationship between herbicide use and ADHD. Least squares dummy variable (LSDV) method and within method using two-way fixed effects was used to elucidate the relationship between glyphosate use and all-listed ADHD hospital discharges. We show that a one kilogram increase in glyphosate use, in particular, in one year significantly positively predicts state-level all-listed ADHD discharges, expressed as a percent of total mental disorders, the following year (coefficient = 5.54E-08, p<.01). A study on the effect of urbanization on the relationship between glyphosate and ADHD indicates that the relationship is marginally significantly positive after multiple comparison correction only in urban U.S. counties (p<.025). Furthermore, total glyphosate use is strongly positively associated with total farm use of nitrogen fertilizers from 1992 to 2006 (p<.001). We present evidence from the biomedical research literature of a plausible link among glyphosate, nitrogen dysbiosis and ADHD. Glyphosate use is a significant predictor of state hospitalizations for all-listed ADHD hospital discharges, with the effect concentrated in urban U.S. counties. This effect is seen even after controlling for individual state characteristics, strong correlations over time, and other significant associations with ADHD in the literature. We draw upon the econometric results to propose unique mechanisms, borrowing principles from soil and atmospheric sciences, for how glyphosate-based herbicides may be contributing to the rise of ADHD in all populations.
Highlights
Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder whose incidence worldwide has increased substantially in recent decades
While we have shown that glyphosate herbicide resistance events and farm use of nitrogen fertilizers are strongly associated with estimated glyphosate use, neither phenomenon can fully explain the increase in all-listed ADHD hospital discharges in our time period of study
We have shown that agricultural estimated glyphosate use and total food and industrial use of maize grain are significant lagged predictors of all-listed ADHD hospital discharges in Healthcare Cost and Utilization Project net (HCUPNET) reporting states from 2007 to 2010 even after controlling for state fixed effects, strong correlations over time, and other documented associations with ADHD in the literature
Summary
Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder whose incidence worldwide has increased substantially in recent decades. The Center for Disease Control’s (CDC) parent report data on ADHD among U.S children indicate a sharp rise beginning in 2007 [1]. According to the CDC, symptoms of ADHD include “a persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development” [2]. Yerys et al [4] reported that ADHD symptoms in children with autism spectrum disorders (ASD) resulted in a greater autistic trait with more significant impairments in working memory and adaptive behavior. It was shown that deficits in executive function were more severe and persistent in patients with ADHD than with ASD [5]. Nydén et al [6] found adults with ADHD, in comparison to ASD and ADHD/ASD groups, experienced more significant neuropsychological impairments in exercises designed to measure intellectual ability along with attention and executive function
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