Hydrolyzed collagen, sourced in the trials reviewed here from fish, bovine, porcine, or chicken, supports skin hydration and skin elasticity in pooled randomized trials and is associated with lower knee joint pain scores versus placebo in studies.
Skin trials used 0.6 to 12g/day, most falling between 2.5 and 10g/day.
Musculoskeletal trials converge on 15g/day for at least 8 weeks alongside training, and the one 12-month bone trial used 5g/day.
Proposed mechanism: small collagen peptides such as Gly-Pro-Hyp have been detected in blood after oral intake and reported to reach skin, but the downstream fibroblast signaling step is inferred rather than measured in these trials.