 Type 1 diabetes is an autoimmune disease that typically strikes children and young adults, in which your own immune system attacks and destroys the insulin-producing cells of your pancreas. If untreated, it's deadly, but even with well-managed insulin replacement, you could cut a decade off your life. Families are devastated when a child receives a diagnosis of type 1 diabetes. Thus, one of modern medicine's holy grails is to understand what causes the body to attack itself in hopes that we can prevent and cure it. Genetic susceptibility plays an important role, but the concordance for type 1 diabetes is only about 50% among identical twins, meaning even if someone with the same DNA as you gets the disease, it's only about a 50% chance you'll get it, too, meaning there must be external factors as well. Some countries have low rates, some have high rates. Japan, for example, has type 1 diabetes rates 18 times lower than the United States, and that's not just genetic, since when children migrate, they tend to acquire the risk of their new home, suggesting it's got to have something to do with the environment, diet, or lifestyle. In fact, the incidence rates vary more than 350-fold around the world. Some countries have hundreds of times higher rates than others, and it's on the rise. Researchers looked at 37 populations from around the world, and the incidence is going up about 3% a year. In fact, I couldn't find a single population going the other direction, 3% higher every year. Our genes don't change that fast. Something is going on. Starting right around World War II, best evidence available suggests type 1 diabetes showed a stable and relatively low incidence over the first half of the 20th century, followed by a clear increase around the middle of the century, and the question is why? A number of factors have been postulated for tipping children over into diabetes, including vitamin D deficiency, certain infections, or exposure to cow's milk. Decades ago, cross-country comparisons like this were published showing a tight correlation between milk consumption and the incidence of type 1 diabetes, insulin-dependent childhood onset diabetes, showing as much as 94% of the geographic variation in incidence might be explained by differences in milk consumption alone. This country, with the highest rates at the top, in Finland, led much of the research into this area. It all started with studies like this, showing the less babies are breastfed, the higher the rate of type 1 diabetes, leading to the obvious conclusion breast milk protects newborn infants. On the other hand, if they're not getting breast milk, they're getting formula which contains cow's milk proteins. In the first few months of life, the gut is especially leaky to protein, so maybe as our immune system attacks the foreign cow proteins, our pancreas gets caught in the crossfire. But this was based on animal experiments. Insusceptible mice, a diet containing the cow's milk protein, casein, produced diabetes. But it doesn't cause diabetes in rats. So are we more like mice or rats? Researchers drew blood from children with type 1 diabetes to see if they had elevated levels of antibodies that attack bovine proteins compared to controls. And every single one of the affected kids had elevated anti-bovine protein antibodies circulating in their blood, compared to much lower levels in the control subjects. Okay, that seems pretty convincing. But what about Iceland? Do they drink more milk than Finland, yet have less than half the type 1 diabetes? We'll cover the Icelandic paradox next.