Most of us grow up learning the basics of the body — the heart, the lungs, the stomach, maybe even a bit about the immune system.
The endocrine system is usually glossed over, if it’s mentioned at all, which is strange given the role it plays in how we grow, sleep, reproduce, handle stress, and stay in balance over time.
Before we get into endocrine disruption — and whether chemicals like glyphosate-based weedkillers might interfere with hormones — it’s worth slowing down to understand what the endocrine system actually is.
What Is the Endocrine System?
Think of it as the body’s long-distance messaging network. The nervous system works fast, sending electrical signals that read more like quick shouts, built for real-time reactions. Hormones work differently: they’re chemical messengers released into the bloodstream and carried throughout the body, slower and quieter, more like letters being delivered.
These messages come from a set of glands — the pituitary, thyroid, adrenals, pancreas, ovaries, and testes among them. The U.S. National Institute of Environmental Health Sciences describes these glands as producing hormones that act as signaling molecules once released into the circulatory system, and the system as a whole as controlling processes from normal growth through fertility and reproduction.
If the nervous system keeps you alive moment to moment, the endocrine system keeps things in balance over the long term.
Why the Endocrine System Matters
Hormones influence far more than most people realise. They help regulate metabolism, hunger and satiety, stress response, sleep, growth, fertility, sexual maturation, mood, memory, immune function, and bone health.
The EPA’s own description of the endocrine system notes it regulates biological processes from conception through old age, including brain and nervous system development, reproductive growth and function, and metabolism and blood sugar regulation. When those signals are disrupted, effects can be subtle at first — fatigue, mood changes, cycle irregularities — or more pronounced, depending on timing and exposure.
Tiny Signals, Big Effects
One of the more counterintuitive aspects of hormones is that they don’t need large changes to produce large outcomes. Hormones operate at extraordinarily low concentrations — researchers describing this scale often reach for the analogy of a teaspoon of salt dissolved in an Olympic-sized swimming pool. At that level of precision, even small interference can matter.
What Is an Endocrine Disruptor?
The World Health Organization defines endocrine disruptors as exogenous compounds or mixtures that alter the function of the endocrine system and consequently cause adverse effects in an organism, its offspring, or a population — a definition widely adopted across EU regulatory frameworks. The U.S. EPA frames it more simply: chemicals that mimic, block, or otherwise disrupt the normal function of hormones.
The EPA notes that disruption can take several forms: a chemical might mimic a hormone and cause the body to over-respond, block a hormone’s effect at the receptor, or directly stimulate or suppress hormone production, leading to over- or under-activity in organs like the thyroid. The disruption doesn’t have to be dramatic or shut a system down — sometimes it only changes how a signal is sent or received. That subtlety is part of what makes endocrine disruption difficult to study, and contested.
Why Timing Matters More Than Dose
A key finding in endocrine research is that when exposure happens can matter as much as how much. Pregnancy, infancy, childhood, and puberty are periods of intense hormonal signalling, and the EPA’s own research has documented effects in these windows: in one EPA study, offspring of pregnant rats exposed to chemicals that reduced serum hormone levels by less than 25 percent still showed measurable effects on neuronal development.
This is part of why questions about endocrine disruption become especially relevant in discussions of low-level, everyday exposure — including residues that may occur in food, water, or other environmental contact. It’s the focus of No More Glyphosate NZ’s ongoing independent testing program, which has tested products including honey, bread, breakfast cereals, oats, wine, and potatoes. Results vary by product and batch — some come back clean, others don’t. The most recent honey testing, for example, found glyphosate in four out of five retail samples, with one result exceeding New Zealand’s legal limit. Because testing is ongoing, we’ve linked to the full results page above rather than a single figure, so you can see the latest findings as they’re published.
This timing principle is also the throughline for the rest of this series. In Is Glyphosate an Endocrine Disruptor? The Evidence, we look at what lab, animal, and wildlife studies actually show. In What Endocrine Disruption Means for People, Animals, and the Environment, we trace how that interference plays out beyond the lab — in fertility trends, livestock, and ecosystems. And in Why Regulators Miss Glyphosate’s Endocrine Risks, we look at why testing frameworks built decades ago still struggle to catch it.
Why Regulators Struggle With Endocrine Disruption
Most chemical regulation, including in New Zealand, was built around traditional toxicology, which generally assumes higher doses cause greater harm and that there’s a threshold below which no effect occurs.
Endocrine disruption doesn’t reliably follow that model. Some hormone-active chemicals show what researchers call non-monotonic dose responses, where low doses can produce effects that aren’t predictable from what happens at higher doses — a finding that’s well documented but also genuinely contested within the field. We unpack that debate, and what it means for how glyphosate has been assessed, in Why Regulators Miss Glyphosate’s Endocrine Risks, the final article in this series.
Why the Endocrine System Matters in Discussions About Glyphosate
It’s difficult to assess claims about glyphosate and hormonal health — fertility, cancer risk, developmental timing — without first understanding how finely tuned the endocrine system is. Once you understand how hormonal messaging works, the next questions follow naturally: can chemicals interfere with those messages, how would we detect it, and are current testing systems built to notice when it happens?
Coming Up in This Series
The endocrine system isn’t fragile in the sense of being weak, but it is precise and highly dependent on timing. Understanding that is the first step in making sense of the broader conversation around endocrine disruption.
In the next article, we’ll look at what the science actually says about glyphosate and hormonal interference, and why that evidence remains one of the more contested areas in chemical safety research.
Part of The Endocrine Disruption Series: Understanding Hormones in a Chemical World
This article is part of The Endocrine Disruption Series, a four-part exploration of what the endocrine system is, how delicate it really is, and what happens when glyphosate-based weedkillers and other modern chemicals interfere with the body’s hormonal messaging system.
1. What Is the Endocrine System? (You’re here)
A simple guide to hormones, how they work, and why even tiny shifts can matter.
2. Is Glyphosate an Endocrine Disruptor?
We examine what the science actually shows — from human cells to wildlife.
3. What Endocrine Disruption Means for People, Animals, and the Environment
The real-world consequences beyond the lab.
4. Why Regulators Miss Glyphosate’s Endocrine Risks
How outdated testing frameworks keep New Zealand in the dark.
Resources & References
Most of what we’ve been taught about hormones is oversimplified. We’re told they operate like on/off switches, rising and falling in neat, predictable ways. But once you start reading the science, a different picture emerges — one where tiny shifts matter, timing matters even more, and chemicals we’ve been told are “safe” have the ability to whisper into the body’s communication system in ways we rarely measure.
If you’d like to explore this further — or see why scientists around the world are raising red flags — these resources are a good place to start.
Internal Articles (NoMoreGlyphosate.nz)
Glyphosate and Hormone Disruption — What We Know So Far
A clear, accessible overview of the emerging science linking glyphosate-based weedkillers to hormonal disturbances, including fertility, thyroid, and metabolic effects. URL: https://nomoreglyphosate.nz/glyphosate-hormone-disruption/
Glyphosate and Male Fertility: What the Science Is Telling Us
A deep dive into animal and human studies showing reduced sperm quality, disrupted testosterone balance, and testicular effects linked to glyphosate exposure. URL: https://nomoreglyphosate.nz/glyphosate-male-fertility/
Glyphosate in NZ Honey: First Test Results
Independent testing showing glyphosate residues in NZ honey — a real-world example of chemical exposure relevant to endocrine risk. URL: https://nomoreglyphosate.nz/glyphosate-in-nz-honey-first-test-results/
Glyphosate in Weet-Bix and Other Cereals
NZ-based cereal and grain testing results, reinforcing why endocrine-disrupting chemical exposure through food matters. URL: https://nomoreglyphosate.nz/weet-bix-glyphosate-test-results/
Scientific & Educational Resources
Endocrine Society — Endocrine Disrupting Chemicals Fact Sheet
A trusted, plain-language explanation from the world’s leading endocrine authority, covering how hormones work and why endocrine disruptors matter. URL: https://www.endocrine.org/patient-engagement/endocrine-library/edcs
World Health Organization (WHO) & UNEP — “State of the Science of Endocrine Disrupting Chemicals”
The landmark global review explaining how endocrine disruption works, why timing matters more than dose, and how chemicals interfere with hormonal systems. URL: https://www.who.int/publications/i/item/9789241505031
Birnbaum LS — “State of the Science of Endocrine Disruptors”
A concise NIEHS commentary summarizing the WHO/UNEP 2012 report and its definition of endocrine-disrupting chemicals. URL: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3620755/
National Institute of Environmental Health Sciences (NIEHS) — Endocrine Disruptors Overview
A reader-friendly summary of endocrine disruptors, how they affect development, fertility, and metabolism, and why low-dose exposure is concerning. URL: https://www.niehs.nih.gov/health/topics/agents/endocrine
US EPA — Overview of Endocrine Disruption
The EPA’s own framework for how chemicals can mimic, block, or otherwise interfere with hormone function. URL: https://www.epa.gov/endocrine-disruption/overview-endocrine-disruption
Peer-Reviewed Research on the Endocrine System & Low-Dose Effects
Vandenberg et al. (2012) — “Hormones and Endocrine-Disrupting Chemicals: Low-Dose Effects and Nonmonotonic Dose Responses”
A foundational scientific paper showing why traditional toxicology misses endocrine effects — crucial context for understanding glyphosate debates. URL: https://doi.org/10.1210/er.2011-1050
Gore et al. (2015) — “EDCs and Developmental Origins of Health and Disease”
Explains how exposure during pregnancy, infancy, and puberty can have lifelong effects on fertility, metabolism, and cancer risk. URL: https://doi.org/10.1210/er.2015-1093
Diamanti-Kandarakis et al. (2009) — “Endocrine-Disrupting Chemicals: An Endocrine Society Scientific Statement”
A comprehensive review outlining the mechanisms and health impacts of endocrine-disrupting chemicals, including reproductive and metabolic effects. URL: https://doi.org/10.1210/er.2009-0002
Glyphosate-Specific Endocrine Research (Foundational Studies)
Thongprakaisang et al. (2013) — “Glyphosate Induces Human Breast Cancer Cell Proliferation via Estrogen Receptors”
A pivotal study showing glyphosate can act like estrogen in human cells — one of the earliest endocrine red flags. URL: https://pubmed.ncbi.nlm.nih.gov/23756170/
Gasnier et al. (2009) — “Glyphosate-Based Herbicides Are Toxic and Endocrine Disruptors in Human Cell Lines”
Early evidence that Roundup formulations disrupt aromatase (a key hormone enzyme) at extremely low doses. URL: https://www.sciencedirect.com/science/article/abs/pii/S0300483X09003047
Romano et al. (2010) — “Prepubertal Exposure to Commercial Glyphosate Formulation Alters Testosterone Levels and Testicular Morphology”
A widely cited animal study demonstrating that early-life exposure to a glyphosate-based herbicide reduced testosterone levels and caused structural changes in developing testes — strong evidence of endocrine disruption. URL: https://pubmed.ncbi.nlm.nih.gov/20012598/
Environmental Endocrine Disruption
Howe et al. (2004) — “Toxicity of Glyphosate-Based Pesticides to Four North American Frog Species”
Demonstrates that glyphosate-based formulations can be highly toxic to developing amphibians and discusses their potential as endocrine disruptors, given frogs’ reliance on thyroid hormones for development. URL: https://pubmed.ncbi.nlm.nih.gov/15352482/
Taken together, these studies tell a story our regulatory system has never truly confronted: endocrine disruption isn’t about high doses, dramatic poisonings, or immediate symptoms. It’s about subtle interference. It’s about long-term patterns. And it’s about what happens when a chemical touches the body at the exact moment a developing organ, gland, or brain circuit is trying to form.
The science is there. The question now — uncomfortable as it is — is whether we’re willing to look at it.
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