Exposure to glyphosate, the active ingredient in many weed killers, is linked to changes in hormones that support pregnancy and fetal development, according to a University of Michigan School of Public Health study. Researchers observed shifts in estriol, thyroid hormones, and corticotropin-releasing hormone among 752 pregnant women in Puerto Rico.
How does glyphosate exposure affect hormones during pregnancy?
The study, published in the Journal of Exposure Science and Environmental Epidemiology, identifies a connection between herbicide exposure and hormonal fluctuations necessary for a healthy pregnancy. Researchers tracked the levels of glyphosate and AMPA—the primary substance glyphosate breaks down into—in urine samples taken from participants at 18, 22, and 26 weeks of pregnancy.
The findings suggest that these chemicals may disrupt the endocrine system through several specific pathways:
Estriol and thyroid hormone shifts
The research team noted a direct correlation between chemical levels and the hormone estriol, which is critical for maintaining pregnancy. According to the study data:
- Moderate increases in AMPA were associated with a 10.6% decrease in estriol levels.
- Moderate increases in glyphosate were linked to an 8.3% decrease in estriol levels.
Additionally, AMPA exposure was linked to higher levels of the thyroid hormone T3. As the pregnancy progressed, researchers found that AMPA was associated with higher thyroid-stimulating hormone, while glyphosate was linked to higher levels of corticotropin-releasing hormone (CRH), a hormone involved in the body’s stress response and the biological processes that trigger labor.
AMPA is the main environmental byproduct of glyphosate. Because it is highly persistent, it often appears in human biological samples even when the original glyphosate has already begun to degrade.
Why were exposure levels higher in Puerto Rico?
The study utilized data from the PROTECT birth cohort, a long-term study focused on environmental exposures and maternal health in Puerto Rico. Researchers found that glyphosate and AMPA were present in 70% of the urine samples collected during the study visits.
Mislael Valentín-Cortés, a postdoctoral research fellow at the University of Michigan and the study’s first author, noted that these exposure levels exceed what is typically reported for the general population in the United States. Valentín-Cortés stated that US territories often carry a disproportionate share of environmental burdens, which are frequently compounded by extreme weather events and infrastructure failures.
Can this study prove glyphosate causes pregnancy complications?
While the data shows a clear link, the researchers cautioned against assuming direct cause and effect. The study was observational, meaning it identifies correlations between chemical presence and hormone levels rather than proving the herbicide is the sole cause of the changes.
There are several limitations to consider:
- Recent Exposure: Urine samples reflect recent contact with chemicals rather than total exposure throughout the entire pregnancy.
- Outcome Data: The study did not measure whether these specific hormonal changes directly resulted in preterm births or specific health issues for the children.
However, the findings provide a biological explanation for previous human studies that have linked glyphosate to preterm birth and differences in fetal growth. By identifying hormone disruption as a potential pathway, the research moves the discussion from general environmental concern to measurable physiological changes.
“This is the most extensively used herbicide in the world, yet there are shockingly few research studies on the potential impacts it may have on human reproductive health, pregnancy, or fetal and child development,” said John Meeker, professor of Environmental Health Sciences at the University of Michigan School of Public Health.
What happens next in environmental health research?
The University of Michigan research team plans to use future data collections to explore whether these hormonal shifts lead to specific birth outcomes or long-term health effects in children. As public interest in pesticide regulation grows, researchers are calling for more sustained attention to how common environmental exposures impact maternal and child health.
When reviewing environmental health studies, always distinguish between observational data (which shows links) and experimental data (which can demonstrate causation).
Frequently Asked Questions
What is glyphosate?
Glyphosate is the active ingredient in many widely used weed killers. It is used extensively in farming, landscaping, and residential lawn care.
How can people be exposed to glyphosate?
Exposure can occur through contact with treated soil or plants, pesticide drift in the air, and through contaminated food or water sources.
Is glyphosate exposure common?
Yes. In the Puerto Rico study, glyphosate and its byproduct AMPA were found in 70% of the participants’ samples.
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