What Causes Hypothyroidism?

In an earlier post I wrote, “Hypothyroidism is so common I suspect an environmental cause.” In fact, I suspect that all common diseases are caused (= made much more likely by) differences between modern life and Stone-Age life. Since then, thanks to comments and email, I have learned more about hypothyroidism. According to Dennis Mangan, it has become a lot more common during the last 100 years, which implies an environmental cause. The most common type of hypothroidism is called Hashimoto’s thyroiditis. It is an autoimmune disorder where the immune system attacks the thyroid, damaging it. A reader with hypothyroidism wrote me:

When I was first tested for thyroid levels, part of the test (which I think is standard protocol) was to test the level of antibodies to thyroid. My levels were off the charts.

This supports what I said. I’m sure that autoimmune diseases are caused by one particular difference from Stone Age life: lack of bacteria in our food. The immune stimulation the harmless bacteria provided can be provided in other ways — bee stings, for example. But I don’t think Stone-Age people got a lot more bee stings than we do.