What is insulin primarily used to treat?

Insulin is primarily used to treat diabetes, a condition characterized by high blood glucose levels due to the body's inability to produce adequate insulin or respond appropriately to insulin. In individuals with type 1 diabetes, the pancreas does not produce insulin at all, necessitating insulin replacement therapy to help manage blood sugar levels. For those with type 2 diabetes, insulin may be used alongside other medications when blood sugar levels remain uncontrolled with oral medications alone. Insulin works by facilitating the uptake of glucose into cells for energy, thus lowering blood sugar levels and helping to maintain overall metabolic balance.

While hypertension, asthma, and cholesterol levels are important health concerns that require appropriate management, they do not involve insulin as part of their treatment. Hypertension is managed with antihypertensive medications, asthma with bronchodilators and corticosteroids, and cholesterol with statins or other lipid-lowering agents. Therefore, the application of insulin is specific to diabetes management, making it the correct answer in this context.