Hi, thank you for your question. Hyperthyroidism can be caused by a number of reasons as listed below.

Graves’ disease is an autoimmune condition in which your immune system is faulty and produces antibodies stimulating your thyroid to produce too much thyroxine (thyroid hormone, T4). This is the most common cause of hyperthyroidism.
Another cause of hyperthyroidism is hyperfunctioning thyroid nodules, which comprises of thyroid adenoma and toxic multinodular goitre.

A thyroid adenoma is an overgrowth of your normal thyroid tissue, which is non-cancerous and is not something serious unless it causes symptoms. Toxic multinodular goitre happens when ultiple nodules are formed in your thyroid causing enlargement of the thyroid gland. Both thyroid adenoma and toxic multinodular goitre causes hyperthyroidim by the production of too much T4.

Sometimes you can also have thyroiditis (inflammation of your thyroid gland) after pregnancy, because of an autoimmune condition or for some unknown reasons. This inflammation can cause excess thyroid hormone stored in the thyroid gland to leak into your bloodstream.

You are at risk of getting hyperthyroidism if you have a family history of thyroid disease, especially Graves’ disease. Other risk factors of hyperthyroidism are your sex, age, history of other autoimmune disorders (type 1 diabetes, rheumatoid arthritis), pregnancy or recent childbirth, and emotional or physical stress. Women are more likely to develop hyperthyroidism.

People below the age of 40 or above the age of 60 have increased risk.
There is nothing you can do to to prevent hyperthyroidism. What you can do is go for regular check ups and your doctor will test your thyroid hormone levels once every year if you have a family history of Graves’ disease.

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