Hydrolyzed Collagen for Skin Aging Meta‐Analyses Are Unreliable

ABSTRACT Background Scientific evidence for oral collagen supplementation in skin aging remains controversial and limited, with various trials finding conflicting results on skin parameters such as reduction in wrinkle depth, increases in hydration and elasticity. These parameters are measured with a variety of methodologies, and recent meta‐analyses have attempted to synthesize existent evidence to ascertain potential benefits. The question of whether these measures are readily comparable, however, has led to concerns about the internal validity and interpretability of these efforts. Aims To investigate major existing meta‐analyses on oral collagen supplementation and perform a technical re‐analysis of both methodology and reported results, as well as a full meta‐regression of constituent collagen studies accounting for dose effects to ascertain evidence quality. Methods Data investigation and evidence appraisal of the methodology of existing meta‐analyses of collagen supplementation and implementation of meta‐regression accounting for cumulative dose effects. Results In both identified meta‐analyses, we find inaccurate reporting of data from primary studies and inappropriate combinations of measures likely to give rise to spurious results. Meta‐regression of collagen studies accounting for dose variations in primary studies found no evidence of benefit from collagen supplementation. Conclusion In sharp contrast to the reported results from prior meta‐analysis, this investigation does not find evidence of benefit for supplementation from existing collagen studies. Evidence synthesis for collagen studies needs a stronger methodological underpinning if results are to be clinically relevant.