Do your kidneys age at a different rate than your liver?

The kidney ages in a measurable, well-documented way. Filtering capacity declines by an average of 6.3 ml/min per 1.73 m² of body surface area per decade in healthy people. At the same time, the outer layer of the kidney shrinks, the number of functioning filter units decreases, and scar tissue develops. This is a universal and predictable pattern, demonstrated across multiple studies in carefully selected healthy kidney donors.

A declining kidney function does not automatically mean that someone is ill. Commonly used formulas for calculating kidney function underestimate that function in older adults by 16 to 25 percent. As a result, some healthy older people are incorrectly labelled with 'chronic kidney disease'. The boundary between normal ageing and actual disease is therefore thinner in the kidney than the numbers sometimes suggest.

The liver ages too, but far less can be said about how quickly that happens. What is known is that the liver breaks down medications less efficiently at older ages. However, the available studies provide no concrete figures on this. A direct comparison of the ageing rate of the kidney and the liver is therefore not possible based on current research.

Another notable point about the kidney: daily function may still be reasonably adequate at older ages, but the reserve capacity is smaller. During acute illness or exposure to harmful substances, the older kidney is therefore more vulnerable than a younger kidney. This is clinically relevant, but says nothing yet about how the liver holds up in the same situation.