In the seemingly never-ending debate over the merits of organic versus conventionally grown food, there is enough scientific research out there to argue fiercely and convincingly on either side. But now you might have a new, surprising reason to be wary of the pesticides in your produce: diabetes.
Maybe. A new study found that exposure to pesticides–through everyday sources like fruits and vegetables or nearby farms–could increase the risk of the disease by 60%. While there is still much to learn about how pesticides interact with the human body, it adds to a growing body of research on the long-term damaging effects of the chemicals that surround us in modern society.
In the study, released at the annual meeting of the European Association for the Study of Diabetes (EASD) in Stockholm last month, a group of researchers found that pesticide exposure was associated with a 60% increase in the risk of type 2 diabetes. The researchers–from Oxford, Brown University, Imperial College London, and the University of Ioannina in Greece–analyzed the results of 25 previously released studies on the health effects of pesticide exposure. The studies dated from the 1980s to 2014, and looked at the effects of a range of different pesticides that have been banned in the U.S., Europe, and much of Asia for up to 40 years, but are still used elsewhere, on a total of about 80,000 subjects, spanning several countries. The majority of the studies focused on environmental exposures–through the food chain or nearby farms–rather than direct users like farm or chemical manufacturing workers.
The EASD group did several different analyses of these studies, and consistently got the same results: an associated rise of about 60% increased relative risk for diabetes. Still, they admit that the initial studies had flaws and their conclusions are not so clear-cut.
“Pesticides are used to kill living organisms. . . . They clearly have a toxic effect,” says Fainia Kavvoura, one of the study coauthors and a lecturer on diabetes at Oxford. “How toxic they are to humans is a much more complex question.”
Through their analysis, researchers found that exposure to certain pesticides, like DDT, seem to confer a greater risk for type 2 diabetes. Their results also suggest that the measurement or method of exposure did not seem to impact risk estimates, which could suggest that any exposure to pesticides could be harmful. But Kavvoura is quick to emphasize that they did not find evidence that pesticides actually cause diabetes, and that more work needs to be done to understand the precise relationship between the two.
“We can’t really tell if there was a causative effect or not,” she said. Kavvoura and her colleagues plan on further analysis to adjust for obesity and high body mass index (BMI) rates, which would strengthen their conclusions, and they plan to publish their full findings in the future.
Every five minutes, two people in the U.S. die of diabetes-related causes, and 16 more adults are diagnosed with the disease, according to the Centers for Disease Control and Prevention. The number of diabetic Americans has quadrupled between 1980 and 2012. At that rate, as many as one-third of adults in the country could have diabetes by 2050.
Globally, diabetes diagnoses have skyrocketed in recent decades, particularly in fast-growing developing countries where a burgeoning middle class has eagerly adopted the poor diet and exercise habits of the West. Recent research found that between 1990 and 2013, the prevalence of diabetes across the globe increased by 45% (the same report found an increase of over 70% in the U.S. over the same period).
Still, the causes of diabetes are not fully understood. The exact cause of type 1 diabetes–an autoimmune condition unrelated to obesity–remains unknown, though some scientists believe it could be triggered by a virus. Type 2 diabetes, by far the more common diagnosis around the world, is known to be related to obesity, poor eating habits, and some genetic triggers. But Kavvoura notes that the reality is more complicated, and environmental aspects play a meaningful role.
“All these factors are interconnected,” she said. “More people are overweight and obese now than in the last 20 to 30 years. But Europeans don’t have as much diabetes as people in Southeast Asia. We know there is something to do with the physiology of these individuals and the way they store fat.”
Fat cells might also be the key to understanding how pesticides could potentially raise the risk of diabetes. Existing research has looked at several different theories, but Kavvoura says the most plausible might be that pesticides accumulate in the body by sticking to fat cells, and are then released into the bloodstream. “Because the pesticide is there and it gets into your circulation, it exerts its effect on other cells in your body, which could lead to light toxicity, insulin resistance, and, eventually, diabetes.”
Meanwhile, scientists are gaining a better understanding of the long-term effects of pesticides, whether through the kind of direct exposure experienced by farmworkers or through consumption of fruits and vegetables containing residual pesticides. One of the longest and broadest studies on the effects of pesticide exposure is out of the University of California-Berkeley, where researchers have been following around 600 residents of the agricultural hub of Salinas, California, from birth through adolescence. The study–known as C.H.A.M.A.C.O.S. and recently profiled by Mark Bittman for The New York Times—has shown links between pesticide exposure in the womb and mental development issues for children later in life.
One of the most significant findings by Kavvoura and her colleagues in their recent review was that the pesticides under study have been banned for several decades. “The fact that you are still seeing the effect of these pesticides even though they were banned 40 years ago, it is quite significant,” she said. “The pesticides stay in your body for a long time and exert their effect for a long time.”
Still, she doesn’t interpret this fact as a signal to go organic full-time. Instead, she says that strong oversight of the farming and chemical industries is essential to supporting public health.
“This emphasizes the need for a worldwide control on pesticides for the ones that we know are harmful, but also for any pesticides currently in development . . . to make sure all effects are monitored over the long term,” she said.
“It’s important that people are able to go to their grocery store and trust what they are buying, and are able to trust their regulatory authorities.”