The study, titled “Association of urinary metabolites of organophosphate and pyrethroid insecticides, and phenoxy herbicides with endometriosis,” was published in Environment International.
The specific causes of endometriosis are still not fully known. Likely, the cause is multifactorial, involving a combination of genetics, environmental exposures, and hormonal imbalances.
Exposure to insecticides — specifically, chemicals used to kill insects — has been linked with increased risks of certain reproductive abnormalities, such as abnormal semen. It has been proposed that such exposures also could increase endometriosis risk, though there isn’t yet enough data to say for sure.
To learn more, researchers analyzed the urine of 594 women, ages 18-44, who underwent surgery (laparoscopy/laparotomy) or pelvic MRI, both of which can help to diagnose endometriosis. Of these women, 202 were diagnosed with endometriosis.
By analyzing the urine, researchers could identify metabolites of insecticides — the compounds generated by the body processing those chemical treatments. In total, 11 metabolites were analyzed; overall exposure rates ranged from 0.80% to 100%, depending on the individual compound.
The researchers noted that levels of several of these metabolites tended to be higher among people who were younger, non-Hispanic black, and less affluent, suggesting individuals with these demographic features may be at a higher risk of pesticide exposure.
Statistical models were then constructed to compare the relative risk of endometriosis based on pesticide exposure.
The results showed that those more exposed to a metabolite called IMPY had a significantly increased endometriosis risk — by about 89%. However, this was only statistically significant when the analysis was limited to people who had been diagnosed surgically, which is generally considered more reliable. When looking at the whole group, the trend was still there, but it was no longer significant — that is, it was impossible to rule out the possibility that the difference was just due to random chance.
Another metabolite, TCPY, was significantly associated with an increased endometriosis risk — by about 65% — among the whole group. But this significant association was not found for the highest exposure group; it was found for the second group. This is still relative to the lowest group — that is, the elevated risk was found in those who had comparatively higher levels of TCPY — but the lack of significance at the higher exposure levels make it difficult to draw definitive conclusions about this result.
“Our preliminary evidence suggests that exposure to diazinon (the parent compound of IMPY) as well as chlorpyrifos and chlorpyrifos-methyl (parent compounds of TCPY) may be associated with increased odds of an incident endometriosis diagnosis,” the researchers said.
However, the investigators noted that this study was limited by its small sample size and by the fact that only one urine measurement was taken. Overall, the study identified an interesting pattern that awaits further validation by future researchers, they said.
“Our findings should be considered as exploratory and warrants further corroboration,” the researchers said. “These observations emphasize the need for further studies that examine endometriosis following exposure to chlorpyrifos and diazinon.”