All of the following hormones regulate calcium levels EXCEPT which one?

Aldosterone is a hormone primarily involved in the regulation of sodium and potassium levels in the body, rather than calcium levels. It functions mainly by increasing the reabsorption of sodium in the kidneys, which in turn affects fluid balance and blood pressure.

In contrast, parathyroid hormone, vitamin D, and calcitonin are directly involved in the regulation of calcium homeostasis. Parathyroid hormone increases calcium levels in the blood by stimulating osteoclast activity, increasing intestinal absorption of calcium, and promoting renal reabsorption of calcium. Vitamin D also plays a crucial role by enhancing calcium absorption in the intestines and facilitating mobilization of calcium from bone. Calcitonin, produced by the thyroid gland, decreases blood calcium levels by inhibiting osteoclast activity and promoting calcium deposition in bone.

Therefore, while parathyroid hormone, vitamin D, and calcitonin are all critical in maintaining calcium balance, aldosterone does not play a direct role in this regulation, making it the correct answer to the question.