Subscribe

Join the PCN mailing list.

Glyphosate and leukemia

The Global Glyphosate Study results for leukemia in lab rats are consistent with:
1. trends in human leukemia incidence; and
2. increasing use of glyphosate since the 1980s.


Glyphosate and glyphosate-based herbicides (GBHs) cause leukemia in young laboratory rats, according to the long-term results of the Global Glyphosate Study (GGS). The first of a series of findings on various health conditions were presented at the annual Ramazzini Days on October 25th, and posted as a pre-print on November 16, 2023.

The Collegium Ramazzini is an independent, international academy composed of physicians, scientists, and scholars from 35 countries. In 2023, scientists are wrapping up the long-term results of the Global Glyphosate Study, assessing effects of glyphosate and glyphosate-based herbicides (GBHs) in over 1000 animals. Sprague-Dawley rats were used in the study (a common research animal).  Over an initial 13 week pilot study researchers reported shifts in the microbiome and the development and endocrine system 

The GGS reported leukemia in the first half of life in exposed animals, which is remarkable because leukemia is exclusively a disease of aging in unexposed Sprague-Dawley rats. So we ask, what evidence addresses GBHs and leukemia in human adolescents and younger adults? Although non-Hodgkin’s lymphoma is caused by glyphosate exposures, significant associations with leukemia were not reported in authoritative reviews by the U.S. Agency for Toxic Substances and Diseases Registry (ATSDR), or the International Agency for Research on Cancer (IARC).

With human data lacking, it may be tempting to dismiss the GGS leukemia results as not relevant. Here we examine the plausibility that the animal results reflect potential glyphosate-related leukemia in North America.

Global Glyphosate Study Leukemia Results

The first GGS long-term findings, on leukemia highlight a potential role for GBHs in earlier-life leukemia (teen to mid-life) in humans, that has not been studied to date. The presentation at Ramazzini Days 2023, in Bologna Italy, illustrated that the about half of the deaths from leukemia (6/13) in study animals occurred during the first year of life (these rats live about two years).

This early onset leukemia is extraordinary, first because leukemia is very rare in the Sprague-Dawley rats—a common research animal, that was used in this work. Leukemia is so rare in this species that it has not been seen at all, during the first year of life in thousands of unexposed “control” animals in long-ongoing research at the Ramazzini Institute (RI) and at the U.S. National Toxicology Program (NTP).

Leukemia deaths in Sprague-Dawley rats exposed to glyphosate and GBHs, in the long-term Global Glyphosate Study

J-shaped curve of global leukemia incidence vs age in 1990 and 2017

Glyphosate-related leukemia in this younger age range has not been reported in human epidemiology studies to date—not necessarily because leukemia was not occurring, but because it is less common, and thus under-studied. The pesticide exposure epidemiology studies largely focused on long term farm workers, and could well have missed increasing leukemia in this age group. Children and spouses were rarely included in farm workers’ studies.

How do the GGS leukemia results compare with the disease trend in humans? The first year of life of Sprague-Dawley rats corresponds roughly to the first half of the human lifespan. This is the period of life when the least leukemia is diagnosed in humans, as reported in a global study of leukemia. Variants of leukemia are diagnosed in the very young, but otherwise leukemia is mostly a disease of aging. Leukemia in humans is rarest in the stage of life that was susceptible to glyphosate and GBHs in the GGS.

Leukemia incidence globally, by age

J-shaped curve of global leukemia incidence vs age in 1990 and 2017
Leukemia Incidence by Age, 1990 to 2017

In the U.S., leukemia is increasing most rapidly in adolescents and younger adults

Leukemia may be rare in adolescents and younger adults, but is the incidence changing in humans in the age group comparable to that highlighted in the GGS?

Yes.

The U.S. Surveillance, Epidemiology and End Results (SEER) program compiles health data, including varieties of leukemia, and makes detailed results available online. The 15 to 39 year old grouping in the SEER database is closest to the age range of rats in which the unexpected leukemia cases occurred in the GGS. Since the early 1990s, leukemia has been increasing at 1.1% per year in this age group—the most rapid rate of increase in any age range reported in SEER data. Disease incidence increased from about 2.5 to 3.5 cases per 100,000 individuals.

Leukemia incidence, 15-39 year olds, 1975 to 2020
U.S. SEER data

Subtitle for This Block

Title for This Block

Text for This Block

Delay-adjusted SEER Incidence Rate, Both Sexes, All Races / Ethnicities

Methodology

Rates are per 100,000 and are age-adjusted to the 2000 US Std Population (19 age groups – Census P25-1130).
NOTE: the final point was affected by disruptions resulting from the COVID-19 pandemic.

The Annual Percent Change (APC) and Average Annual Percent Change (AAPC) estimates were calculated from the underlying rates using the Joinpoint Trend Analysis Software, Version 4.9, March 2021, National Cancer Institute using the default settings.

The APC’s/AAPC’s direction is “Rising” from 1990 on (1.1% per year); the entire 95% confidence interval (C.I.) is above 0. Earlier, the trend is considered “Not Significant.”

SEER*Explorer: An interactive website for SEER cancer statistics [Internet]. Surveillance Research Program, National Cancer Institute; 2023 Apr 19. [updated: 2023 Jun 8; cited 2023 Nov 14]. Available from: https://seer.cancer.gov/statistics-network/explorer/. Data source(s): SEER Incidence Data, November 2022 Submission (1975-2020), SEER 8 registries.

Correlation between glyphosate use and leukemia trend

The last piece of the puzzle is how glyphosate use has changed over time. Is there a reason to associate the herbicide use with the observed increasing trend for leukemia starting around 1990?

Glyphosate entered the U.S. market in 1974, as a defoliant. It was initially popular for removing all plant life on transportation corridors, sports facilities, military grounds, as well as in forestry and to alter aesthetics. Agricultural use accelerated during the 1990s, with the advent of genetically modified glyphosate-resistant crops. The graph below depicts increasing use in agriculture (but omits other uses, as listed above).

Thus, increasing use of glyphosate correlates with increasing leukemia rates.

Glyphosate use in agriculture, 1992-2014
U.S. Department of Agriculture

Conclusion

The GGS leukemia in rats, reported by the Ramazzini Institute scientists, is consistent with the here-to-fore unexplained increasing leukemia in adolescents and younger adults. The incidence has been increasing 1.1 percent per year in the U.S., since the early 1990s. The U.S. SEER data shows that leukemia has been increasing most quickly in this age group, from about 2.5 cases per 100,000 per year in 1990 to more than 3.5 cases per 100,000 at present.

The timing of increasing human leukemia in adolescents and younger adults corresponds to increasing use of glyphosate.

The GGS results are a substantial addition to knowledge about the world’s most-used herbicide. They provide further strong reasons to shift to least-toxic pest control, to protect public health as well as biodiversity. For sustainable agriculture it is essential to support, conduct research, and learn from organic and low-input farmers.

It has been about a year since Canada hosted COP-15 on the Convention on Biological Diversity, and Canada has committed to halving risks and use of pesticides by 2030. This is one goal worth surpassing, to protect biodiversity as well as public health!

What You Can Do: Support organic agriculture, and tell your MPs and Ministers that we need to shift to low input farming. Find their contact information here.