A steroid hormone secreted by the adrenal cortex that serves as the body’s chief regulator of salt, water, and blood pressure. When blood volume or sodium falls, the kidneys release renin, triggering a cascade that ends with aldosterone instructing the kidneys to retain sodium and excrete potassium, with water following the sodium to restore volume. This elegant feedback loop keeps blood pressure stable across varying salt intakes and fluid losses. Disorders of excess cause hypertension with low potassium, while deficiency contributes to the salt-wasting crisis of Addison disease. Common blood pressure drugs, including ACE inhibitors, work partly by reducing aldosterone’s effects. Dietary sodium intake interacts directly with this system, which is why salt sensitivity varies between individuals and why aldosterone sits at the center of hypertension nutrition advice.