Is There a Link Between Disordered Eating and Hypothyroidism?

I recently saw someone posting about being diagnosed with hypothyroidism and having to deal with the fact that they “caused it” with their extreme dieting. I was diagnosed with Hashimoto’s hypothyroidism at about 22 (I’m now 40), after multiple years of extremely restrictive “yo-yo” dieting as a teenager/tween. I had never heard of this possible link between disordered eating and hypothyroidism—is there any evidence for it?

—Teenage Dieter

Hashimoto’s hypothyroidism is an underactive thyroid that happens when the virus-fighting subset of white blood cells attack the thyroid. As with many autoimmune diseases, some people are genetically predisposed to develop autoimmunity. Disease occurs when they are exposed to a trigger. A number of things are thought to trigger the immune system to attack the thyroid, including some viruses, physical stress like puberty, or emotional stress like a job loss.

In theory, the physical stress of an eating disorder could trigger the immune system to attack the thyroid, but there is no published data to suggest eating disorders are a common cause of Hashimoto’s hypothyroidism.

The truth is we rarely identify the specific trigger that causes an individual to develop Hashimoto’s disease. This is because the trigger can set off the inflammation long before someone becomes hypothyroid. In fact, some people have markers of an autoimmune attack on the thyroid and never develop an underactive thyroid. There is also no proven intervention to treat the attack on the thyroid and prevent the thyroid from becoming underactive. As a result, there is not a strong incentive to identify people with markers of thyroid inflammation but normal thyroid function.

Both restrictive and overnourished eating disorders have direct effects on thyroid function. This makes sense when you consider that one of the thyroid’s main jobs is to regulate metabolic rate. I think the easiest way to conceptualize this is to think of the thyroid like a gas pedal in a car. If you increase thyroid hormone levels, you step on the gas, making the metabolism pick up speed. If you decrease thyroid hormone levels, you let off the gas, decreasing the speed of the metabolism. But these thyroid changes look different than Hashimoto’s because they start in the hypothalamus in the brain and the pituitary gland, not in the thyroid gland the way Hashimoto’s hypothyroidism does. This type of hypothyroidism typically resolves when the eating disorder is in remission.

The upshot: While eating disorders can affect thyroid hormone levels, they are not specifically associated with Hashimoto’s hypothyroidism. Typically, we can’t identify the specific trigger for Hashimoto’s disease in most individuals.