This 2000 study of human cartilage and skin used a slow chemical change in protein, the build-up of D-aspartic acid, to estimate how long collagen stays in place. It put the half-life of cartilage collagen at 117 years and skin collagen at 15, and showed slow turnover is why sugar damage builds up in cartilage.
The researchers compared collagen from human articular cartilage and from skin across a range of ages. They measured three advanced glycation end products (AGEs), the chemical marks sugars leave on long-lived proteins, and the proportion of D-aspartic acid, which slowly rises the longer a protein stays in a tissue. From how fast that proportion rose with age, they calculated a half-life for each collagen.
AGEs and D-aspartic acid both rose in a straight line with age, in cartilage and in skin collagen. AGEs built up faster in cartilage, and D-aspartic acid was higher there, showing cartilage collagen stays in the tissue longer. Once turnover was allowed for, AGEs accumulated at the same rate in both collagens, so turnover was the main reason cartilage collects more of them. The calculated half-life of cartilage collagen was 117 years, against 15 years for skin collagen.
The abstract does not give the number of donors or their ages. The half-life is an estimate calculated from a chemical marker, not a direct count of new collagen being made, and it is an average across the tissue. The study does not show whether turnover changes after an injury, and it tested nothing that might change it.
A half-life of 117 years means adult cartilage collagen is close to permanent. That is why researchers treat type II collagen loss so seriously: the cells cannot replace it at anything like the rate an enzyme such as MMP13 can cut it. The paper also ties long-lived collagen to the build-up of sugar damage.
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