In some individuals, immune system proteins called autoantibodies bind to the thyroid gland, reducing its ability to produce hormones and triggering persistent inflammation.

This study found that certain antibodies in some people block selenium from reaching the thyroid, which stops the thyroid from making enough active hormone — causing fatigue and other symptoms like in hypothyroidism. This supports the idea that antibodies can mess up thyroid function.

This study found that people with antibodies attacking their thyroid also had signs of inflammation and poor thyroid function, which means these antibodies are likely causing damage and making the thyroid work less well.

This study showed that when a drug calmed down the immune system in someone with Hashimoto’s, their thyroid started working normally again and they didn’t need hormone pills anymore — proving that the immune system’s attack on the thyroid was causing the problem.