Science reports:

Eight years ago, Bhanudas More went for a routine blood test. More, a farmworker in this small village in Maharashtra state, was lean, worked long hours in the fields, and seemed healthy, so the result startled him. He was diagnosed with type 2 diabetes, a disease commonly associated with sedentary life in the city.

Medication did little to bring his condition under control. He also began to experience persistent bloating and stomach discomfort. “I was taking the medicines, but I still didn’t feel normal,” says More, who is now 56. “Some days, it was hard to get through the work.”

The source of his problems remains mysterious, but doctors uncovered a clue when they asked about his working conditions. In the sugarcane and grape fields where he labors, More is routinely exposed to a mix of crop pesticides. A rapidly growing body of research suggests those chemicals may disrupt the gut microbiome, the ecosystem of trillions of bacteria, fungi, and viruses that help digest food, produce essential nutrients, train the immune system, and send chemical signals that influence metabolism and even brain function. Such disruptions could lead to a host of medical problems, researchers say, among them the global rise of type 2 diabetes in nonobese people.

Those who are exposed on the job, like More, may be at the highest risk, but pesticides used on crops or in homes may also affect the microbiome. “If you expose it repeatedly to low doses of bioactive chemicals you may not see an immediate dramatic effect, but you can create a long-term selective pressure,” says Robin Mesnage, scientific director at the Buchinger Wilhelmi clinics and visiting research fellow at King’s College London.

So far, there’s no solid evidence of harm to human health. And scientists caution that many other factors, including diet, lifestyle, and genetics, influence the gut microbiome, which makes teasing out the effects of pesticides difficult.

In 2023, pesticide use reached 3.73 million tons globally, roughly twice the amount used in 1990. (India saw an almost 20% increase just in the past decade.) Research on the health risks has long focused on acute poisoning, neurotoxicity, and cancer. But new genetic tools for studying diverse microbial ecosystems have made it possible to track pesticides’ effects on the microbiome. [Continue reading…]