Summary: A UC Davis-led study found that pregnant women who take at least 800 micrograms of folic acid around the time of conception may reduce their children’s risk of autism spectrum disorder (ASD) associated with household and agricultural pesticide exposures.
Source: UC Davis.
High Folic Acid Intake Around Conception May Lower Pesticide-Related Autism Risk
Researchers at UC Davis and partner institutions report new evidence that maternal folic acid supplementation around the time of conception is associated with a reduced risk of autism in children exposed prenatally to certain pesticides. The study, using data from the Childhood Autism Risks from Genetics and the Environment (CHARGE) study, appears in Environmental Health Perspectives and suggests that recommended folic acid levels — roughly 800 micrograms, the amount present in many prenatal vitamins — may partially attenuate pesticide-related ASD risk.
The research compared 296 children clinically diagnosed with ASD to 220 children with typical development, all born in California between 2000 and 2007 and enrolled in CHARGE at ages 2 to 5. Investigators collected maternal reports of household pesticide use and dietary supplement intake through interviews, and they used California’s pesticide application records linked to residential addresses to estimate local agricultural pesticide exposure.
Key findings indicate that mothers who reported taking at least 800 micrograms of folic acid during the critical window around conception had a lower estimated risk of bearing a child with ASD, even when exposed to pesticides. Conversely, mothers taking less than 800 micrograms and reporting pesticide exposures—especially repeated or long-term household exposure—showed substantially higher estimated odds of having a child with ASD. Similar elevated risks appeared for low folic acid intake combined with agricultural pesticide exposure occurring within three months before to three months after conception.
“We found that if the mom was taking folic acid during the window around conception, the risk associated with pesticides seemed to be attenuated,” said Rebecca J. Schmidt, assistant professor in the Department of Public Health Sciences and the study’s first author. She emphasized that avoiding pesticide exposure during pregnancy is preferable, but acknowledged that women living near agricultural areas may have limited control over drift, and adequate folic acid intake could offer some protective benefit.
The study found that the combination of lower folic acid intake (<800 μg daily) and indoor pesticide use was associated with higher odds of ASD (adjusted odds ratio [OR]=2.5, 95% confidence interval [CI]: 1.3–4.7) compared to the reference group of high folic acid intake (≥800 μg) without pesticide exposure. When low folic acid intake was combined with repeated household pesticide exposures—such as routine pet pesticide treatments or outdoor sprays and foggers—the estimated odds rose to approximately 3.9–4.1 in some analyses. For agricultural exposures around conception, combinations of low folic acid and specific pesticide groups (chlorpyrifos, organophosphates, pyrethroids) produced estimated ORs around two times higher than either exposure alone.
Although the findings are compelling, the investigators caution that the case–control design relies on retrospective reporting and cannot establish causation. Memory recall and other confounding factors could influence results, and the authors call for larger, prospective and mechanistic studies to confirm and clarify the pathways involved.
Folic acid and folate are critical for DNA methylation, repair, and synthesis—processes that are especially important during rapid cell division and fetal development. Schmidt noted that adequate folic acid may support genomic functions that help protect the developing brain from environmental insults, although the exact protective mechanisms remain to be clarified.
Authors on the study include Rebecca J. Schmidt, Janie F. Shelton, Lora Delwiche, Robin L. Hansen, Sally Ozonoff, Deborah H. Bennett, Irva Hertz-Picciotto, Daniel J. Tancredi, and Heather E. Volk (UC Davis); Vladimir Kogan and Heather E. Volk (UCLA); and Claudia C. Ma, Erin C. McCanlies, and others affiliated with the National Institute for Occupational Safety and Health.
Funding: This research was supported by the National Institute of Environmental Health Sciences, the National Institute of Child Health and Human Development (part of the NIH), the Environmental Protection Agency STAR program, and the UC Davis MIND Institute.
Abstract (Condensed)
This case–control analysis examined combined maternal folic acid (FA) supplementation and pesticide exposures in relation to ASD among California children enrolled in the CHARGE study. Mothers’ supplemental FA and household pesticide use were collected retrospectively; agricultural exposures were estimated from state pesticide application records linked to residential addresses. High FA intake (≥800 μg) during the first month of pregnancy without pesticide exposure served as the reference. Compared with this group, low FA (<800 μg) combined with indoor or agricultural pesticide exposures was associated with higher adjusted odds of ASD than either exposure alone. Results suggest that higher maternal FA intake around conception may attenuate the association between prenatal pesticide exposure and ASD risk. Confirmatory and mechanistic studies are warranted.