leucine

Protein builds muscle and bone. The reason why you need more, the older you get, is that your ability to digest and absorb amino acids — the “building blocks” of protein structures, reduces over time. You need more, just to stay at the same level.

There are two musculoskeletal conditions that can arise from insufficient protein: sarcopenia and osteoporosis. Sarcopenia is age-related muscle loss and function. Osteoporosis is loss of bone density.