Collagen vs Vitamin C
for skin
Stronger evidence: tie
Stronger effect: Vitamin C
Safety: No notable interactions recorded for either.
For skin, the two are evidence-matched; the difference is in effect and safety.
Collagen
grade C low certainty
small improvements in skin elasticity/hydration in industry-funded trials
2.5–10 g/day
Vitamin C
grade C low certainty
topical better-supported than oral; oral may support collagen synthesis
500 mg/day, adults
sources: PMID:00000028 · PMID:42095579