The Link Between Diabetes, Pesticides and PCBs

With commentary by Ioanna Tzoulaki, PhD, lead author of the meta-analysis and senior lecturer in Epidemiology, Imperial College London’s School of Public Health, UK

pesticidesNew research presented last week at the annual meeting of the European Association for the Study of Diabetes (EASD) in Stockholm adds weight to the growing body of evidence linking endocrine-disrupting chemicals (EDCs) with diabetes.

One study—a meta-analysis of 21 earlier studies involving more than 66,000 people—found that exposure to any type of pesticide was associated with a 61% increased risk of diabetes, with some pesticides appearing riskier than others.

A separate study of 639 women in Crete, Greece, found that those who had elevated blood levels of polychlorinated biphenyls (PCBs) during the first trimester of pregnancy were more than four times as likely to develop gestational diabetes.

“The findings are interesting scientifically as they help us understand which disease pathways may be affected by pesticides,” said Ioanna Tzoulaki, PhD, lead author of the meta-analysis and senior lecturer in Epidemiology, Imperial College London’s School of Public Health, UK.

Indeed, the meta-analysis echoes in human populations what researchers have demonstrated in animal and laboratory studies: Exposure to endocrine-disrupting chemicals can provoke precursors to diabetes and even diabetes itself.

EDCs have been shown to do everything from slash insulin levels and raise serum glucose to set-off hyperinsulinemia, worsen glucose tolerance, and insulin sensitivity and reduce insulin-stimulated glucose uptake. The chemicals are also capable of altering the expression of genes, which in at least one study led to a rise in blood glucose levels analogus to those seen in adult-onset diabetes.

The Crete study, meanwhile, sheds light on a less-studied phenomenon: The ability of EDCs to raise the risk of diabetes developed during pregnancy. "Our findings support the idea that early-life exposure to endocrine disruptors may exacerbate gestational diabetes,” said principal investigator Leda Chatzi, PhD, assistant professor of epidemiology and nutrition at University of Crete, Heraklion, Greece. “It is important to develop interventions in pregnancy, including dietary and lifestyle changes, to minimize the effects of early-life exposure to persistent organic pollutants.”

Both authors acknowledge that their studies are observational and that lifestyle factors including diet, weight and exercise are critically connected with diabetes. But the role of chemicals cannot be ignored, they say.

"We often think of insulin resistance as a consequence of overeating and lack of exercise," says Laura Vandenberg, PhD, assistant professor of environmental health at University of Massachusetts, Amherst. “But chemical exposure can promote insulin resistance, too."

Chemicals known as endocrine disruptors—so-called for their ability to interfere with the body’s endocrine system—have come under scrutiny in recent years amid mounting evidence of their association with health problems ranging from developmental and reproductive disorders to cancer, obesity, and more recently for their link with diabetes.

Results from animal models, human clinical observations and epidemiological studies converge to implicate EDCs as a significant concern to public health, reports the Endocrine Society.

A large number of chemicals have been identified as endocrine disruptors, among them certain pesticides and organic pollutants such as those in the two studies: DDT, dieldrin, heptachlor, HCB and PCBs.

Even though some endocrine-disrupting chemicals like the pesticide DDT and PCBs, used in electrical equipment, were banned in the 1970s in the U.S., they are still used or have been used more recently in other parts of the world. And the very qualities that made them so effective for industrial and agricultural use—their ability to stick around and get the job done—are the same ones that make them hazardous to public health and the environment: The chemicals are slow to degrade and can persist in the environment for decades. People around the world continue to be exposed through air, soil, water and food.

“When considering the reality that diabetes is rising in every country worldwide, and that environmental pollutants are abundant, there is a real urgency for prospective, high-quality research, said Lisa Staimez, PhD, assistant professor at Emory Global Diabetes Research Center at Emory University in Atlanta. “That research should in turn inform policies aimed at reducing the burden from diabetes.”

More than a billion pounds of pesticides are used each year in the U.S., according to the Environmental Protection Agency. The vast majority are applied on crops, but the chemicals are also used on golf courses and lawns and in schools and homes. Not all have been fully tested for their endocrine-disrupting abilities. Pesticides include herbicides, which are used to control weeds; insecticides, which are used to control insects; and fungicides, which are used to prevent mold.

Meanwhile, rates of diabetes and other metabolic diseases have risen dramatically over the last several decades. Globally, more than 170 million people suffer from diabetes—a number some researchers say will reach 366 million by 2030. 

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