What's causing the diabetes epidemic in the United States? Poor diet, lack of exercise, obesity, and a smoking habit are commonly cited as the big factors. But what about pollution in the environment, and specifically air pollution? Could small particles from haze, smoke and car exhaust have a hand in doubling the number of diagnosed cases of the disease over the last 15 years?
A new study argues there is a strong link between pollution and diabetes rates, and that even current pollution limits set by the Environmental Protection Agency may not be stringent enough to protect us from harm.
Measuring the health effects of particulate pollution is a tricky business — generally speaking, the smaller the particle, the more easily it can get inside your lungs and into your bloodstream. Studies suggest that anything smaller than ten micrometers in diameter (about a tenth the diameter of a human hair) is problematic, increasing the risk of asthma, heart disease, and stroke.
The EPA's threshold for safe exposure to PM 2.5 particles, as they're called, is 15 micrograms per cubic meter of air. That's a kind of a lot to wrap your head around, but the point is this — the researchers found that diabetes rates started creeping up even in areas with significantly lower pollution levels than the EPA threshold (see figure above).
In fact, in some areas the range from lowest to highest pollution levels (still below EPA threshold) corresponded with a 20 percent uptick in diabetes prevalence.
Why would tiny particles of toxic chemicals affect our ability to process glucose? At this point, the researchers aren't sure. As team member John Brownstein of Children's Hospital Boston said in a press release:
“We didn’t have data on individual exposure, so we can’t prove causality, and we can’t know exactly the mechanism of these peoples’ diabetes,” acknowledges Brownstein. “But pollution came across as a significant predictor in all our models.”
Previous studies in mice have suggested that air pollution is associated with insulin resistance, a precursor condition to type 2 diabetes. This is the first to show the relationship in people, and it is far from the end of the story. Much more work will need to be done to untangle how other environmental pollutants — like the plastic additive bisphenol A — may also contribute to America's ballooning diabetes problem.
Figure: Diabetes Care