Why does kidney function decline with age?

As the body ages, kidney function naturally declines due to several physiological changes. A primary factor is a gradual reduction in blood flow to the kidney, which is essential for its filtration processes. Additionally, there is a loss of nephrons—the functional units responsible for filtering waste and balancing fluids—and a decrease in the activity of cellular enzymes.1

These changes result in a reduced ability of the kidney to concentrate urine, meaning a larger volume of water is required to excrete the same amount of waste material. While these age-related shifts are normal, they are distinct from chronic kidney disease, which involves progressive, pathological damage to the nephrons often driven by conditions like hypertension or diabetes. In healthy aging, the reduction in renal function is typically balanced by a decrease in the body's overall excretory load, such as reduced muscle mass and lower metabolic activity, preventing the dangerous accumulation of waste products in the blood.12