A recent publication in JAMA, Arsenic Exposure and Prevalence of Type 2 Diabetes in US Adults raises the question, does arsenic in the drinking water increase the risk of type 2 diabetes? The authors' answer is a definite "maybe."
The study evaluated arsenic levels in people who had participated in the 2003-2004 version of th National Health and Nutrition Examination Survey (NHANES), and who had urine arsenic levels obtained. The NHANES study is ongoing, and is considered to be a representative sample of US adults: more information on NHANES is available at the CDC's website.
Why arsenic? Well, maybe because NHANES collected lots and lots of lab results, and urinary arsenic levels was one of them. So was cadmium, and that generated an earlier publication that cadmium might be suspect: Urinary Cadmium, Impaired Fasting Glucose, and Diabetes in the NHANES III was published in 2003 in Diabetes Care.
That article, BTW, mentioned that "epidemiologic studies have implicated arsenic as a possible
cause of type 2 diabetes, and a role for other environmental toxins is strongly
suspected." Other toxins? Well, lead, mercury, beryllium for instance: these are frequently called "heavy metals."
So the present study is not news. It's another example of data-mining. Look at a big database for an association; in this case T2DM and heavy metals. You'll find inevitably find a few associations, some of which are self-evident, and some of which are unexpected.
To give an analogy: it's like looking for your next automobile at a used car lot. You'll see some red cars, some with flat tires, some with leather-wrapped steering wheels. Inevitably, some of these cars will fail your mechanic's inspection: for instance, those with flat tires won't pass. But deciding whether those with red paint are likely to fail inspection is a guess -- maybe there's a true association, based on the driving habits of people who choose brightly-colored cars. Or maybe it's just random luck.
Same with this study. Maybe it's a true association; maybe it's just random luck. So the authors are correct to conclude that "Prospective studies in populations exposed to a range of inorganic arsenic levels are needed to establish whether this association is causal." Until such studies are done, it's only speculation.