What hormone disorder is key in Graves' disease?

Graves' disease is characterized by the overproduction of thyroid hormones, specifically thyroxine (T4) and triiodothyronine (T3). This excess hormone production results from an autoimmune response where the body's immune system mistakenly stimulates the thyroid gland, leading to hyperthyroidism. The condition often presents with symptoms such as weight loss, increased heart rate, heat intolerance, and nervousness, which are all indicative of heightened metabolic activity due to elevated thyroid hormone levels.

While each of the other options refers to different hormonal disorders, they do not pertain to Graves' disease. For instance, underproduction of thyroid hormones would be associated with conditions like Hashimoto's thyroiditis, lack of insulin relates to diabetes, and excess cortisol secretion is linked to Cushing's syndrome. Therefore, the focus on the overproduction of thyroid hormones as the fundamental disturbance in Graves' disease distinctly identifies why this is the correct answer.