How do the kidneys change during aging?

As the human body ages, the kidneys undergo physiological changes that primarily affect their ability to concentrate urine. This decline in concentrating capacity means that a larger volume of water is necessary to excrete the same amount of waste material.1

These changes are driven by several factors:
* Reduced Blood Flow: There is a gradual decrease in the blood supply to the kidneys over time.1
* Loss of Nephrons: The nephrons, which serve as the functional units of the kidney, are gradually lost.1
* Cellular Activity: The activity of cellular enzymes within the kidneys is reduced.1

Despite these shifts, the kidneys typically maintain enough functional capacity that waste products do not accumulate in the blood under normal conditions; such accumulation is generally a sign of disease rather than typical aging. The impact of these changes on daily life is often mitigated by a lower excretory load, resulting from reduced physical activity, changes in diet, and a decrease in muscle mass.1