How strong is the evidence for Collagen?

Multiple independent meta-analyses of randomized trials find oral hydrolyzed collagen supplementation improves skin hydration and elasticity and reduces signs of skin aging, a reasonably consistent finding across several independent research groups. That evidence is currently rated moderate (50/100), built on 10 published studies, including 2 randomized controlled trials and 5 meta-analyses -- a reasonable base, but not yet enough for full certainty.