What is the cause behind water loss in diabetes insipidus?

Water loss in diabetes insipidus is primarily caused by a lack of antidiuretic hormone (ADH) production or action. In this condition, the body is unable to effectively concentrate urine due to insufficient levels of ADH, which is responsible for promoting water reabsorption in the kidneys. When ADH is absent or its action is impaired, the kidneys excrete large volumes of dilute urine, leading to significant water loss.

This inadequate reabsorption of water results in increased thirst and the need to drink excessive amounts of fluids to compensate for the loss, which is a hallmark symptom of diabetes insipidus. In contrast, other factors such as renal blood flow, excessive hydration, or high sodium levels in the blood do not directly cause the characteristic water loss seen in this condition. Instead, they might affect fluid balance differently but are not the primary issue in diabetes insipidus.