Collagen powders promise better skin, joints and tendons, and the marketing writes cheques the trials cannot cash. Digestion breaks collagen into amino acids like any protein. One credible lab finding drives the category: taking gelatin with vitamin C before exercise raises collagen-synthesis markers. Markers are not wrinkles or injuries prevented.
The trial most often cited by collagen sellers (Shaw et al.) showed raised circulating markers of collagen synthesis after vitamin-C-fortified gelatin taken before exercise. It measured circulating markers over hours, not skin quality, tendon injury rates or joint pain over time. Cosmetic trials tend to be small, industry-funded and short. Nothing follows users long enough to speak to ageing outcomes.
Doing it: If you want to try it, 15 g with vitamin C about an hour before training mirrors the protocol in the literature. Treat any skin result you notice as a bonus, not evidence. Ordinary protein suffices everywhere else.
Who it suits: Hard to recommend on current evidence. Athletes with tendon niggles have the most plausible use case, ideally with a sports dietitian's guidance.
Sources
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