Kerry Grens writes about a new study conducted in France that showed that farmers who use weedkillers were more than two times as likely to suffer from depression. This story reminds me of the ones about the alarming rates of Indian farmers’ suicides after the “Green revolution” took over there.
Whether the weedkillers are causing depression “is not clear,” said Marc Weisskopf, the study’s lead author and an associate professor at the Harvard School of Public Health. “But (the result) suggests we should not be ignoring herbicides just because they’re targeting plants.”
Earlier research on depression and pesticides has focused on insecticides, particularly organophosphates, which are known to be toxic to nerve cells, said Weisskopf.
Monocrotophos, the insecticide that killed 23 school children in India this month, is an organophosphate, for example.
The use of pesticides has also been linked to Parkinson’s disease among farmers (see Reuters Health story of May 28, 2013 here:).
As part of a study on Parkinson’s disease, Weisskopf and his colleagues assessed the risks for depression with exposure to any kind of pesticide by surveying 567 French farmers about their use of fungicides, insecticides and herbicides.
The team conducted home visits to get a detailed assessment of chemical exposures, including going over bills for pesticide purchases, looking through farming calendars and inspecting old pesticide containers.
They also asked the farmers whether they had ever been treated for depression.
Weisskopf’s group reports in the American Journal of Epidemiology that 83 farmers, about 15 percent, said they had been treated for depression. Forty-seven of them had never used pesticides, while 36 had.
Among the farmers without Parkinson’s disease, 37 who had never used herbicides and 20 who had used the weedkillers reported being treated for depression.
There was no difference in the risk of having depression among the farmers who had used fungicides or insecticides, compared to those who hadn’t used any pesticide.
But when the researchers took into account factors linked with depression, such as age and cigarette smoking, they determined that those farmers exposed to weedkillers were nearly two and a half times as likely to have had depression.
Furthermore, farmers who had greater exposure – either more hours or longer years using herbicides – also had a greater chance of having depression than farmers who had used weedkillers less.
That kind of dose-response relationship is usually thought to support a connection – in this case, between the chemicals and depression. But this type of study cannot prove cause and effect.
One possibility that wasn’t ruled out is that the exposed farmers might have had other health conditions that affected their ability to work, which in turn made them vulnerable to depression.
“The health of the farmer is critical. If they can’t work, they get depressed,” said Cheryl Beseler, a researcher at Colorado State University, who was not involved in this study.
She said the study was otherwise very well done in terms of collecting information about the farmers’ past pesticide use.
The results do not apply to the average gardener, although Weisskopf said it will be valuable to better understand herbicides’ safety in farming and non-farming settings.