Everyone knows that diabetes is associated with obesity, probably because obesity causes diabetes. However, thin people also become diabetic. A clue to why is provided by the correlation between diabetes and what are called “persistent organic pollutants” (POPs). POPs are man-made organic compounds, usually pesticides, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans.
A 2006 study using NHANES (National Health and Nutrition Examination Survey 1999–2002) data found very strong associations between levels of these chemicals and diabetes. For example, a risk ratio of 30. These associations persisted even when the data was stratified in all sorts of ways. The scariest result came from people who had BMI < 25. Looking only at such people, those above the 90th percentile for amount of POPs had 16 times the risk of diabetes as those below the 25th percentile. Here is something associated with thin people getting diabetes.
Does the association exist because POPs cause diabetes? You might argue that POP exposure is correlated with poverty (poor people are more exposed), poor people exercise less than rich people, and lack of exercise causes diabetes. However, Agent Orange exposure among soldiers is associated with diabetes. That is unlikely to be due to confounding with poverty or lack of exercise.
Everyone has these chemicals in their body, but almost no one knows how much. I don’t know if I’m in the 10th percentile or the 90th percentile. If I’m in the 90th percentile, what can I do about it? A good place for self-measurement and tracking.