In a longitudinal study of over 500 Mexican Americans living in southern Texas, researchers found that high levels of toxic metals in urine predicted faster increases in blood sugar over subsequent years.

Based on these results, individuals with the highest levels of arsenic in their urine were projected to qualify as prediabetic 23 months earlier and diabetic 65 months earlier than those with the lowest exposure to the toxic metal.

The study, published in Diabetes Care, highlights an underappreciated risk factor for diabetes, a disease of immense public health significance that is associated with significant health disparities in conditions such as cardiovascular disease, kidney failure and blindness. It also emphasizes that this risk factor can be addressed by reducing exposure to contaminated food, water and other products.

“Environmental exposures have largely been neglected as drivers of the diabetes epidemic,” said Margaret Weiss, an MD/PhD student at UIC and first author of the study. “These data support using environmental policy as a new tool to mitigate the devastating burden of diabetes on individuals and society at large.”

The study examined residents of Starr County, Texas, a region along the U.S.-Mexico border with one of the highest rates of diabetes and diabetes-related mortality in the country. Arsenic and other toxic metals have been detected in local groundwater, and these elements may also be ingested through foods and medicines.

As part of a broader project led by the University of Texas Health Science Center at Houston, 510 participants provided urine and blood samples. Researchers measured the levels of different metals in the urine at the start of the study, then measured blood-sugar levels three, six, 12, 24 and 36 months later.

On average, blood sugar levels increased in all participants. But in those who initially exhibited higher urinary levels of arsenic, selenium, copper, molybdenum, nickel or tin, blood sugar increased at a faster rate over the three years.

This acceleration puts those who started with normal blood sugar levels at risk of developing prediabetes and diabetes earlier than others in their population — a worrisome trajectory, said Dr. Robert Sargis, associate professor in the College of Medicine.

“In clinical medicine, time really matters,” said Sargis, senior author of the study. “The earlier you develop diabetes, the worse the complications are. The longer you have diabetes, the worse the complications are. It underscores the need to engage these folks sooner in the clinic.”

How arsenic and other metals increase the risk of diabetes isn’t completely understood. Other metals, namely cobalt and zinc, were associated in the study with lower blood sugar in subsequent years, suggesting a potentially protective effect of some elements. But the alarming results with arsenic and other toxic metals suggest they are environmental risk factors that could be new targets to prevent the disease.

“Unlike genetics, environments are modifiable. There are things we can do to reduce these exposures,” Sargis said. “We need to start thinking about tools in our toolbox that we haven’t used to address the risk of diabetes, and environmental policy can be an important lever we can pull that will hopefully improve people’s lives.”