Epidemiologic Evidence of Glyphosate’s Carcinogenic Potential

Abstract

Worldwide use of glyphosate has exploded since it was introduced in 1974. Most official assessments have disagreed with IARC’s 2015 conclusion that glyphosate is probably carcinogenic to humans (group 2A). In order to assess as directly as possible whether glyphosate is associated with an increased risk of non-Hodgkin lymphoma (NHL) in humans, we conducted a meta-analysis of the epidemiologic evidence with an a priori focus on high glyphosate exposures. We used six studies, adding the recently published Agricultural Health Study (AHS) results to five older case-control studies. To best address glyphosate’s carcinogenic potential, we focused on the workers in each study with the highest exposure by prioritizing in order: (1) highest cumulative exposure and longest lag, (2) highest cumulative exposure; (3) longest exposure duration and longest lag; (4) longest exposure duration; (5) longest latency or lag; and (6) ever-exposure. This quantification varied by study. We estimated the overall meta-relative risk of NHL to be 1.41 (95% confidence interval: 1.13-1.75). Due to our focus on the highest exposed workers, this is a stronger effect than previously reported. We compare and contrast our results with other meta-analyses and describe our concerns with the exposure assessment in the most recent AHS and its potential to bias the inference towards no increased risk. The AHS exposure group we used in our meta-analysis is likely to provide the least biased exposure effect estimate. Our findings support IARC’s assessment of glyphosate’s carcinogenic potential. This work has received much attention in the popular press and beyond, resulting in accusations of unethical scientific methods, public records requests and subpoenas.