Glyphosate and Autism
Gut dysbiosis plays a role in many neurological diseases, including depression, Alzheimer’s disease, Parkinson’s disease, and autism [52]. There has been growing awareness recently regarding the complex interactions between the gut microbiome and the brain via the highly interconnected gut-brain axis, a bidirectional communication network [53]. Exposure to glyphosate reduces the abundance of a number of different acid-loving species that produce short chain fatty acids (SCFAs) from dietary fiber [54]. The SCFA butyrate delivered to the liver via the hepatic portal vein is detected by sensors in the liver, and a signal is conveyed to nerve centers in the brain via the vagus nerve which enhances sleep quality [55]. Sleep disorder is a prominent feature of autism [56]. As we mentioned earlier, melatonin deficiency caused by glyphosate likely also plays a role [39].
Butyrate induces the differentiation of immune cells into T-regulatory cells (Tregs), which control inflammation [51]. The prevalence of inflammatory bowel disease (IBD) has increased over time closely in step with the rise in glyphosate usage on core crops [57]. Glyphosate was one of the toxic chemicals identified as a contributor to IBD in a recent publication by Chen et al. [58]. Children with autism are at a significant increased risk to IBD, with an odds ratio (OR) of 1.66 (p < 0.001) [59].
Glyphosate exposure to rats for 35 days led to multiple disruptions in the gut. Glyphosate resulted in a decrease in the ratio of villus height to crypt depth in the duodenum and jejunum, a feature associated with celiac disease [60]. In this experiment, glyphosate also caused a decrease in glutathione levels and the activity of antioxidant enzymes, including glutathione peroxidase (Gpx). MDA content was also elevated, indicating PUFA peroxidation. The mRNA expression levels of several proteins associated with inflammation were increased, including interleukin-1β (IL-1β), IL-6, tumor necrosis factor- α (TNF-α), mitogen-activated protein kinase 3 (MAPK3), nuclear factor-κB (NF-κB,) and caspase-3. The relative abundance of Firmicutes andLactobacillus species were reduced, while the abundance of several pathogenic species, mainly Fusobacteria strains, was increased [61]. In a study published in 2022, Fusobacteria were found to be more abundant in the gut of autistic children compared to normal controls [62].
Gluten intolerance is a prevalent feature of autistic children, and many parents have implemented a gluten-free diet with the hope of healing their childrens’ guts [63]. A remarkable case study involved a 5-year-old boy diagnosed with severe autism. Diagnosis of underlying celiac disease motivated implementation of a gluten-free diet along with various nutritional supplements. The child’s gastrointestinal symptoms rapidly improved, and symptoms of autism abated. The authors suggested a malabsorption syndrome associated with central nervous system dysfunction [64]. Glyphosate is commonly used on wheat crops as a desiccant just before harvest, and this has resulted in high levels of glyphosate contamination in wheat-based foods [65]. Glyphosate usage on wheat has increased over time, in step with the rise in celiac disease [66].
Glyphosate has been linked to asthma in both human and animal studies. A study focused on the town of Monte Maíz in Córdoba, Argentina examined a possible relationship between glyphosate and asthma in the population there. This town was selected because it is situated in the middle of an agricultural region where glyphosate is heavily used on genetically modified corn and soy crops. Volatile grain dust from pulverized soy and corn grain husk is stored in huge silos in the town. Winds can easily disperse the dust into the surrounding area. Glyphosate and aminomethylphosphonic acid (AMPA) (a toxic breakdown product of glyphosate) were detected in 100% of the soil samples taken near the silos, and the levels of glyphosate and AMPA far exceeded the levels of any other pesticides. The asthma rates were significantly higher overall in the town compared to the rate in Argentina and were highest for those in close vicinity to the silos. The rate of asthma in the 18–45-year-old population living near the silos was more than double the national average [67]. In another study, mothers with asthma were 62% more likely to deliver an infant later diagnosed with autism [68].
In a study on farmers in North Carolina and Iowa, glyphosate, the most commonly used herbicide there, was significantly associated with both asthma and wheeze, whereas no association was found with the related herbicide glufosinate [69]. Exposure of mice to glyphosate-rich air samples induced IL-13 dependent pulmonary inflammation and induced the release of Th2 cytokines, a likely mechanism for increased asthma risk [70].