Pesticides could make a farmer 80 to 90% more likely to suffer depression.

Earlier this fall, researchers from the National Institute of Health finished up a landmark 20-year study, a study that hasn’t received the amount of coverage it deserves. About 84,000 farmers and spouses of farmers were interviewed since the mid-1990s to investigate the connection between pesticides and depression, a connection that had been suggested through anecdotal evidence for far longer. We called up Dr. Freya Kamel, the lead researcher on the study, to find out what the team learned and what it all means. Spoiler: nothing good.

“There had been scattered reports in the literature that pesticides were associated with depression,” says Kamel. “We wanted to do a new study because we had more detailed data than most people have access to.” That excessive amount of data includes tens of thousands of farmers, with specific information about which pesticides they were using and whether they had sought treatment for a variety of health problems, from pesticide poisoning to depression. Farmers were surveyed multiple times throughout the 20-year period, which gives the researchers an insight into their health over time that no other study has.

Because the data is so excessive, the researchers have mined it three times so far, the most recent time in a study published just this fall. The first one was concerned with suicide, the second with depression amongst the spouses of farmers (Kamel says “pesticide applicators,” but most of the people applying pesticides are farmers), and the most recent with depression amongst the farmers themselves.

“I don’t think there’s anything surprising about the fact that pesticides would affect neurologic function.”